Patent Application
20250136769
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The instant application relates to polymers and polymer compositions. In particular, the instant application relates to highly entangled polymers and polymer compositions.
Some polymers rely on crosslinks to increase stiffness. However, dense crosslinks embrittle polymers, resulting in a stiffness-toughness conflict. In addition, in some polymers, toughness is improved by incorporation of sacrificial bonds, leading to a positive correlation between hysteresis and toughness. There is a need for polymer materials that can achieve high stiffness and toughness while also exhibiting low hysteresis.
In one aspect, an entangled polymer composition includes an entangled polymer network including a plurality of entangled polymers; and a plurality of crosslinks crosslinking the polymers at a density of no more than one crosslink per 1,000 monomer units of the polymer;—wherein the polymer composition has a toughness of at least about 100 Jm−2 and a stiffness of at least about 50 kPa
In some embodiments, the density of the crosslinks crosslinking the polymers is no more than one crosslink per 3,000, 4,000, 5,000 or 8,000 monomer units of the polymer.
In some embodiments, the density of the crosslinks crosslinking the polymers is no more than one crosslink per 10,000 monomer units of the polymer.
In some embodiments, the polymer composition includes about 50, 100, 150, 200, 300, 400, or 500 entanglements per crosslink.
In some embodiments, wherein the polymer composition is an elastomer, and the elastomer has a toughness of at least about 500 Jm−2 and a stiffness of at least about 400 kPa.
In some embodiments, the polymer composition has a stiffness of at least about 100 kPa.
In some embodiments, the polymer wherein the product of the stiffness and the toughness is at least about 104 kPa m−2.
In some embodiments, the polymer composition further includes a solvent and the entangled polymer network is swollen with the solvent.
In some embodiments, the solvent is water and the polymer composition is a hydrogel, and the hydrogel has a toughness of at least about 100 Jm−2 and a stiffness of at least about 50 kPa.
In some embodiments, the solvent is an organic solvent, and the polymer composition is an organogel.
In some embodiments, the polymer composition has a ratio of dissipated energy to applied work that is less than about 10%.
In some embodiments, the polymer composition has a ratio of dissipated energy to applied work that is less than about 5%
In some embodiments, the polymer composition has a nominal tensile strength of at least about 100, 200, 300, or 500 kPa.
In some embodiments, the polymer composition has a strength of at least about 2.5, 2.75, 3.0, 3.25, or 3.5 MPa.
In some embodiments, the polymer composition has a coefficient of friction of less than about 0.05, 0.04, 0.03, 0.02, 0.01, 0.005, or 0.001.
In some embodiments, the polymer composition has a fatigue threshold of at least about 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 300, or 350 Jm−2.
In some embodiments, the polymer composition has a wear rate of less than about 1, 0.5, 0.3, 0.25, 0.2, 0.15, or 0.1 mg/cycle.
In some embodiments, the polymer includes poly(ethyl acrylate), polyacrylic acid, poly(acrylamide), polyethylene glycol, polyvinylpyrrolidone, polyvinyl alcohol, poly(2-hydroxyethyl methacrylate), poly(methacrylic acid), poly(N-isopropyl acrylamide), polyacrylic acid, poly(methyl methacrylate), polymethacrylate, poly(ethyl methacrylate), poly(propyl acrylate), poly(propyl methacrylate), poly(butyl acrylate), poly(acrylic acid), poly(N-isopropyl acrylamide), poly(butyl methacrylate), polyethylene, polypropylene, poly(vinyl acetate), polyacrylonitrile, polybutadiene, polyisobutylene, polyisoprene, polychloroprene, polynorbornene, polytetrafluoroethylene, ethylene acrylate copolymers, poly(ethylene-co-acrylic acid), poly(ethylene-co-ethyl acrylate), poly(ethylene-co-methacrylic acid), poly(ethylene-co-vinyl acetate), poly(acrylonitrile-co-butadiene), poly(isobutylene-co-isoprene), poly(perfluoromethylvinylether), poly(styrene-co-butadiene), polyurethane, polysulfide, polysiloxane, natural rubbers, silicone rubbers, nitrile rubbers, cellulose, alginate, chitosan, hyaluronic acid, collagen, gelatin, or a combination thereof.
In some embodiments, the crosslinks are formed using a crosslinker selected from a group consisting of N,N′-methylenebisacrylamide, Tricyclo[5.2.1.02,6]decanedimethanol diacrylate, benzophenone, glycidyl methacrylate, poly(ethylene glycol) diacrylate, Ethylene glycol diacrylate, 1,4-Butanediol diacrylate, Poly(propylene glycol) diacrylate, Di(ethylene glycol) diacrylate, Bisphenol A ethoxylate diacrylate, 1,3-Butanediol diacrylate, 1,6-Hexanediol diacrylate, Tri (ethyleneglycol) diacrylate, Neopentyl glycol diacrylate, Tetra(ethylene glycol) diacrylate, benzophenone, glycidyl methacrylate, adipic acid dihydrazide, butanediol-diglycidyl ether, citric acid, glutaraldehyde, divinyl sulfone, sulfur, and a combination thereof.
In one aspect, a method of forming an entangled polymer composition includes a) providing a mixture including a plurality of monomers; a plurality of crosslinkers, wherein there are no more than one crosslinker per 1,000 monomers; and a solvent, wherein the molar ratio of solvent to monomer is less than 12; b) polymerizing the monomers to form polymers and entangling the polymers to form an entangled polymer network; and c) forming crosslinks by crosslinking the polymers.
In some embodiments, the density of the crosslinks crosslinking the polymers is no more than one crosslink per 3,000, 4,000, 5,000 or 8,000 monomer units of the polymer.
In some embodiments, the density of the crosslinks crosslinking the polymers is no more than one crosslink per 10,000 monomer units of the polymer.
In some embodiments, the entangled polymer composition includes about 50, 100, 150, 200, 300, 400, or 500 entanglements per crosslink.
In some embodiments, the entangled polymer composition a toughness of at least about 100 Jm−2 a stiffness of at least about 50 kPa.
In some embodiments, the polymer composition is an elastomer, and the elastomer has a toughness of at least about 500 Jm−2 and a stiffness of at least about 400.
In some embodiments, the method further includes swelling the entangled polymer network with a solvent after step c).
In some embodiments, the solvent is water and the polymer composition is a hydrogel, and the hydrogel has a toughness of at least about 100 Jm−2 and a stiffness of at least about 50 kPa.
In some embodiments, the solvent is an organic solvent, and the polymer composition is an organogel.
In some embodiments, the monomers include ethyl acrylate, acrylamide, acrylic acid, 2-Hydroxyethyl methacrylate, ethylene glycol, methacrylic acid, N-isopropyl
Acrylamide, Methyl methacrylate, methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, acrylic acid, methacrylic acid, butyl methacrylate, ethylene, propylene, vinyl acetate, acrylonitrile, butadiene, Isobutylene, isoprene, chloroprene, norbornene, tetrafluoroethylene, or a combination thereof.
In some embodiments, the polymers include natural rubber, silicon rubber, poly(ethyl acrylate), poly(acrylamide), polyacrylic acid, poly(2-hydroxyethyl methacrylate), poly(methacrylic acid), poly(N-isopropyl acrylamide), poly(methyl methacrylate), polymethacrylate, poly(ethyl methacrylate), poly(propyl acrylate), poly(propyl methacrylate), poly(butyl acrylate), poly(butyl methacrylate), polyethylene, polypropylene, poly(vinyl acetate), polyacrylonitrile, polybutadiene, polyisobutylene, polyisoprene, polychloroprene, polynorbornene, polytetrafluoroethylene, ethylene acrylate copolymers, poly(ethylene-co-acrylic acid), poly(ethylene-co-ethyl acrylate), poly(ethylene-co-methacrylic acid), poly(ethylene-co-vinyl acetate), poly(acrylonitrile-co-butadiene), poly(isobutylene-co-isoprene), poly(perfluoromethylvinylether), poly(styrene-co-butadiene), polyurethane, polysulfide, polysiloxane, natural rubbers, silicone rubbers, nitrile rubbers, polyethylene glycol, polyvinylpyrrolidone, polyvinyl alcohol, or a combination thereof.
In some embodiments, the crosslinks are formed using a crosslinker selected from a group consisting of N,N′-methylenebisacrylamide, Tricyclo[5.2.1.02,6]decanedimethanol diacrylate, benzophenone, poly(ethylene glycol) diacrylate, Ethylene glycol diacrylate, 1,4-Butanediol diacrylate, Poly(propylene glycol) diacrylate, Di(ethylene glycol) diacrylate, Bisphenol A ethoxylate diacrylate, 1,3-Butanediol diacrylate, 1,6-Hexanediol diacrylate, Tri (ethyleneglycol) diacrylate, Neopentyl glycol diacrylate, Tetra(ethylene glycol) diacrylate, glycidyl methacrylate, adipic acid dihydrazide, butanediol-diglycidyl ether, citric acid, glutaraldehyde, divinyl sulfone, sulfur, and a combination thereof.
In some embodiments, the molar ratio of solvent to monomer is between about 2 and 12.
In some embodiments, the molar ratio of solvent to monomer is 0.
In some embodiments, the mixture further includes an initiator.
In some embodiments, the initiator includes 2-Hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone, 2-Hydroxy-2-methylpropiophenone, glycidyl methacrylate, 2-oxoglutaric acid, benzophenone, or a combination thereof.
In some embodiments, the molar ratio of initiator to crosslinkers is less than about 1.0.
In some embodiments, the initiator has a molar ratio of initiator to monomer of less than about 10−5.
In some embodiments, forming crosslinks includes crosslinking the polymers at a density of no more than one crosslink per 1,000 monomers.
In one aspect, a method of forming an entangled polymer composition includes a) providing a mixture including a plurality of polymer chains; a plurality of crosslinkers, wherein there are no more than one crosslinker per 1,000 monomers in the polymer chains; and a solvent; b) kneading the mixture of precursors at a temperature of at least about 40° C. to form an entangled polymer network; and c) crosslinking the polymer chains to form crosslinks.
In some embodiments, the density of the crosslinks crosslinking the polymers is no more than one crosslink per 3,000, 4,000, 5,000 or 8,000 monomer units of the polymer.
In some embodiments, the density of the crosslinks crosslinking the polymers is no more than one crosslink per 10,000 monomer units of the polymer.
In some embodiments, the entangled polymer composition includes about 50, 100, 150, 200, 300, 400, or 500 entanglements per crosslink.
In some embodiments, the entangled polymer composition a toughness of at least about 100 Jm−2.
In some embodiments, the polymer composition is an elastomer, and the elastomer has a toughness of at least about 500 Jm−2 and a stiffness of at least about 400.
In some embodiments, the method further includes swelling the entangled polymer network with a solvent after step c).
In some embodiments, the solvent is water and the polymer composition is a hydrogel, and the hydrogel has a toughness of at least about 100 Jm−2 and a stiffness of at least about 50 kPa.
In some embodiments, the solvent is an organic solvent, and the polymer composition is an organogel.
In some embodiments, the method further includes annealing the entangled polymer network at a temperature of at least about 40° C. after step b).
In some embodiments, kneading the mixture precursors occurs at a temperature of at least about 50, 60, 70 or 80° C.
In some embodiments, the polymers include polyethylene glycol, polyvinylpyrrolidone, polyvinyl alcohol, poly(2-hydroxyethyl methacrylate), silicone rubbers, nitrile rubbers, poly(methyl methacrylate), polymethacrylate, poly(ethyl acrylate), poly(ethyl methacrylate), poly(acrylamide), polyacrylic acid, poly(methacrylic acid), poly(N-isopropyl acrylamide), poly(propyl acrylate), poly(propyl methacrylate), poly(butyl acrylate), poly(butyl methacrylate), ethylene acrylate copolymers, poly(ethylene-co-acrylic acid), poly(ethylene-co-ethyl acrylate), poly(ethylene-co-methacrylic acid), poly(ethylene-co-vinyl acetate), poly(acrylonitrile-co-butadiene), polyacrylonitrile, polyisobutylene, poly(isobutylene-co-isoprene), poly(tetrafluoro ethylene), poly(tetrafluoroethylene), poly(perfluoromethylvinylether), poly(styrene-co-butadiene), polyurethane, polyisoprene, polychloroprene, polybutadiene, polysulfide, polynorbornene, polysiloxane, polyethylene, polypropylene, poly(vinyl acetate), polyacrylonitrile, cellulose, alginate, chitosan, hyaluronic acid, collagen, gelatin, starch, chitin, agarose, dextran, konjac glucomannan, pullulan, guar gum, polynucleotide, polyisoprene, polyamide, or a combination thereof.
In some embodiments, the crosslinks are formed using a crosslinker selected from a group consisting of benzophenone, glycidyl methacrylate, glyoxal, oxidized dextrin, epichlorohydrin, adipic acid dihydrazide, endogen polyamine spermidine, ethylene glycol dimethacrylate, butanediol-diglycidyl ether, citric acid, glutaraldehyde, divinyl sulfone, and sulfur, and a combination thereof.
In some embodiments, the polymer chains have an average molecular weight of at least about 5×105 g/mol.
In some embodiments, forming crosslinks includes crosslinking the polymer chains at a density of no more than one crosslink per 1,000 monomers in the polymer chains.
In some embodiments, the solvent is less than about 40% of the mixture by mass.
Any one of the embodiments disclosed herein may be properly combined with any other embodiment disclosed herein. The combination of any one of the embodiments disclosed herein with any other embodiments disclosed herein is expressly contemplated.
The objects and advantages will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:
In one aspect, a polymer composition is disclosed, including an entangled polymer network including a plurality of entangled polymers; and a plurality of crosslinks crosslinking the polymers at a density of no more than one crosslink per 1,000 monomer units of the polymer; where the polymer composition has a toughness of at least about 100 Jm−2 and a stiffness of at least about 50 kPa. In some embodiments, the polymer composition includes an entangled polymer network in which entanglements outnumber crosslinks, which resolves the stiffness-toughness conflict and results in materials with both high stiffness and high toughness. In some embodiments, the polymer composition has a toughness of at least about 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, or 1500 Jm−2, or the toughness is in any range bounded by any two values disclosed herein. In some embodiments, the polymer composition has a stiffness of at least about 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200 or 1500 kPa, or the stiffness is in any range bounded by any two values disclosed herein. In some embodiments, the polymer composition has the combination of the toughness of any value or in any range as disclosed herein and the stiffness of any value or in any range as disclosed herein. In some embodiments, the resulting material also has negligible hysteresis.
In one embodiment, a polymer composition is disclosed, including an entangled polymer network swollen with a solvent, including a plurality of entangled polymers; and a plurality of crosslinks crosslinking the polymers at a density of no more than one crosslink per 1,000 monomer units of the polymer; where the polymer composition has a toughness of at least about 100 Jm−2 and a stiffness of at least about 50 kPa. In some embodiments, the solvent is water and the polymer composition is a hydrogel. In some embodiments, the solvent is an organic solvent and the polymer composition is an organogel.
Crosslinks are generally formed by bonds (e.g., physical or chemical bonds) linking polymer chains. In contrast, entanglements form when polymer chains become tangled with each other. These entangled points act as physical crosslinks, stiffening the polymer network like crosslinks. However, entanglements can slip, whereas crosslinks cannot. When the polymer network is stretched, therefore, entanglements slip and deconcentrate tension at short chains, whereas crosslinks cannot avoid stress concentration at short chains. Additionally, entanglements do not result in the formation of bonds (e.g., physical or chemical bonds) linking polymer chains. Instead, the two or more entangled polymer chains interweave together such that the polymer chains cannot be separately from one another without breaking the polymer chains. In some embodiments, the entanglements disentangle under stress when the polymer chains are not crosslinked at all, but do not disentangle when the polymer chains are sparsely crosslinked.
In some embodiments, the entangled polymer compositions described herein have the surprising property that they have high stiffness and toughness while having low crosslinking density. Many polymer materials rely on crosslinks to resist stretching and impart stiffness. However, when crosslinks are dense, the amount of deformation is limited, leading to low toughness. In contrast, in the entangled polymer compositions described herein, entanglements resist stretching, leading to high stiffness, and allow transmission of stress along polymer chains, leading to high toughness. In some embodiments, the density of the plurality of crosslinks crosslinking the polymer chains is no more than one crosslink per 1,000 monomer units of the polymer. Applicants have surprisingly found that when the density of the crosslinks is no more than one crosslink per 1,000 monomer units of the polymer, the resulting polymer compositions exhibited high toughness (at least about 100 Jm-2) and high stiffness (at least about 50 kPa). In some embodiments, the density of the plurality of crosslinks crosslinking the polymer chains is no more than one crosslink per about 2,000, 300, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 15000 monomer units of the polymer, or the density is in any range bounded by any two values disclosed here. In some embodiments, the polymer composition has a toughness of at least about 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, or 1500 Jm−2, or the toughness is in any range bounded by any two values disclosed herein. In some embodiments, the polymer composition has a stiffness of at least about 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200 or 1500 kPa, or the stiffness is in any range bounded by any two values disclosed herein. In some specific embodiments, the polymer composition has a toughness of at least about 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, or 1500 Jm−2, and a stiffness of at least about 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200 or 1500 kPa.
In some specific embodiments, the polymer composition has a toughness of at least about 200 Jm−2 and a stiffness of at least about 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200 or 1500 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 300 Jm−2 and a stiffness of at least about 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200 or 1500 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 400 Jm−2 and a stiffness of at least about 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200 or 1500 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 500 Jm−2 and a stiffness of at least about 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200 or 1500 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 600 Jm−2 and a stiffness of at least about 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200 or 1500 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 700 Jm−2 and a stiffness of at least about 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200 or 1500 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 800 Jm−2 and a stiffness of at least about 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200 or 1500 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 900 Jm−2 and a stiffness of at least about 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200 or 1500 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 1000 Jm−2 and a stiffness of at least about 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200 or 1500 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 1200 Jm−2 and a stiffness of at least about 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200 or 1500 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 1500 Jm−2 and a stiffness of at least about 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200 or 1500 kPa.
In some specific embodiments, the polymer composition has a toughness of at least about 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, or 1500 Jm−2, and a stiffness of at least about 100 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, or 1500 Jm−2, and a stiffness of at least about 200 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, or 1500 Jm−2, and a stiffness of at least about 300 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, or 1500 Jm−2, and a stiffness of at least about 400 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, or 1500 Jm−2, and a stiffness of at least about 500 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, or 1500 Jm−2, and a stiffness of at least about 600 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, or 1500 Jm−2, and a stiffness of at least about 700 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, or 1500 Jm−2, and a stiffness of at least about 800 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, or 1500 Jm−2, and a stiffness of at least about 900 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, or 1500 Jm−2, and a stiffness of at least about 1000 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, or 1500 Jm−2, and a stiffness of at least about 1200 kPa. In some specific embodiments, the polymer composition has a toughness of at least about 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, or 1500 Jm−2, and a stiffness of at least about 1500 kPa.
In contrast, in polymer networks that rely on crosslinks rather than entanglements, herein referred to as “crosslink-dominant polymer networks” 110, shown in
In some embodiments, the polymer compositions disclosed here (also referred to as “entangled polymer compositions”) can be formed using a small amount of solvent and a small amount of crosslinkers. In some embodiments, the entangled polymer compositions can be formed either by synthesis from monomers combined with a small amount of solvent. In other embodiments, the entangled polymer compositions can be formed by forming a dough from long-chained polymers combined with a small amount of solvent. Applicants have surprisingly found that using a small amount of solvent leads to crowding and entanglement of polymer chains. Polymers and hydrogels are often formed using a large amount of solvent, for example, with solvent-to-monomer molar ratios W of greater than about 25.0. In some embodiments, the entangled polymer compositions as described herein, on the other hand, are formed using lower solvent-to-monomer ratios W, for example, less than about 12.0, to form a large number of entanglements. In some embodiments, entangled hydrogel compositions are formed using solvent-to-monomer ratios W of about 2.0-12.0. In some embodiments, entangled hydrogel compositions are formed using solvent-to-monomer ratios W of about 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, or 12.0, or the solvent-to-monomer ratio is in any range bounded by any two values disclosed herein. In some embodiments, the entangled polymer compositions are also formed using a small number of crosslinkers, for example, fewer than one crosslink for 100,0000 monomer units, fewer than one crosslink for 10,000 monomer units, or fewer than one crosslink for 1,000 monomer units. In some embodiments, the entangled polymer composition are formed using fewer than one crosslink per 100,000, 90,000, 80,000, 70,000, 60,000, 50,000, 40,000, 30,000, 20,000, 10,000, 9,000, 8,000, 7,000, 6,000, 5,000, 4,000, 3,000, 2,000, or, 1,000 monomer units, or the number of the monomer units is in any range bounded by any two values disclosed herein. As a result, the number of entanglements greatly outnumber the number of crosslinks. In contrast, crosslink-dominant polymers often have a greater amount of crosslinks, e.g., one crosslink per 100 monomers.
In some embodiments, compared to crosslink-dominant polymer networks, the entangled polymer compositions described herein have high toughness and high stiffness. In other embodiments, the entangled polymer compositions described herein have high strength and negligible hysteresis. As shown in
While a crosslink-dominant polymer has a net-like topology, as seen in
In some embodiments, the entangled polymer composition is a hydrogel. In some embodiments, when polymers are swollen with a solvent, e.g., water, they form gels. When synthesized in the presence of a large amount of solvent, some polymers gel through physical bonds, and others gel by chemical crosslinks. These two classes of hydrogels are exemplified by PVA and PEG. PVA hydrogels form crystalline domains through hydrogen bonds, and these physical hydrogels resist excessive swell, and exhibit high stiffness, strength, toughness, and fatigue resistance. However, during deformation, the hydrogen bonds break and reform, so that PVA hydrogels exhibit pronounced inelasticity. In contrast, dry PEG crystallizes, but dissolves in water, so to resist excessive swell in water, PEG hydrogels generally rely on dense chemical crosslinks, which leads to brittleness. In some embodiments, the entangled hydrogels can resist excessive swell and achieve high stiffness, strength, and toughness while exhibiting low hysteresis by relying on entanglements rather than crosslinks to resist swelling.
In some embodiments, the entangled polymer composition includes a plurality of entangled polymers which cannot be easily disentangled. In other embodiments, the sparse crosslinks prevent the polymer chains from disentangling. In some embodiments, polymer chains are long, leading to high toughness. Non-limiting examples of long polymer chains include polymers having a molecular weight greater than about 5×105 g/mol or greater than about 106 g/mol. In some embodiments, in the entangled polymer composition described herein, the entanglements cannot disentangle without chain scission, and entanglements help to further stiffen the polymer. Therefore, in some embodiments, the stiffening effect of entanglements is more pronounced when the crosslink density is low. In some embodiments, the polymer chains in the entangled polymer composition can slip with low friction, and thus the polymer composition can be loaded cyclically with low hysteresis.
In some embodiments, the entangled polymer compositions have high stiffness and toughness. In some embodiments, the entangled polymer compositions also have negligible hysteresis. In some embodiments, the entangled polymer compositions also have high fatigue resistance under cyclic loading. In some embodiments, the entangled polymer composition is an elastomer. In other embodiments, the entangled polymer composition is submerged in a solvent and swollen to form a gel. In some embodiments, the entangled polymer composition is a gel with low hysteresis, low friction, and/or high wear resistance. In some embodiments, the solvent is water and the gel is a hydrogel. In some embodiments, the entangled polymer composition is transparent.
The polymer content of the entangled polymer composition is relatively insensitive to crosslink fraction within a critical range of crosslink fraction C. As used herein, “crosslink fraction” C refers to the molar ratio of crosslinker to monomer, “solvent fraction” W refers to the molar ratio of solvent to monomer, and “initiator fraction” I refers to the molar ratio of initiator to monomer.
In some embodiments, in entangled polymer compositions, entanglements contribute to high stiffness.
In some embodiments, the polymer composition has a stiffness of at least about 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200 or 1500 kPa, or the stiffness is in any range bounded by any two values disclosed herein. In some embodiments, the stiffness of an entangled polymer composition is between about 50 kPa and about 800 kPa. In some embodiments, the stiffness of an entangled polymer composition is at least about 50 kPa. In some embodiments, the stiffness of an entangled polymer composition is at least about 100 kPa. In some embodiments, the stiffness of an entangled polymer composition is at least about 400 kPa. In some embodiments, the stiffness is 50-100 kPa, 100-200 kPa, 200-300 kPa, 300-400 kPa, 400-500 kPa, or 500-600 kPa, 600-700 kPa, 700-800 kPa, 800-900 kPa, 900-1000 kPa, 1000-1200 kPa, or 1200-1500 kPa. In some embodiments, the entangled polymer composition is an entangled hydrogel, and the stiffness of an entangled hydrogel is between about 50 kPa and about 300 kPa. In some embodiments, an entangled hydrogel has a stiffness of at least about 50, 100, 150, 200, 250, or 300 kPa, or the stiffness is in any range bounded by any two values disclosed herein. In some embodiments, the entangled polymer composition is an entangled elastomer, and the stiffness of an entangled elastomer is about 400-700 kPa. In some embodiments, an entangled elastomer has a stiffness of at least about 400, 450, 500, 550, 600, 650, or 700 kPa, or the stiffness is in any range bounded by any two values disclosed herein.
In some embodiments, the entangled polymer composition shows a high degree of elasticity. In some embodiments, the high elasticity results from several factors. First, even though the crosslinks are sparse, the dense entanglements aid in maintaining the network configuration when the polymer is stretched. Second, polymer chains are long (e.g. having a molecular weight greater than 5×105 g/mol or greater than 106 g/mol) and do not break before the sample fractures. Third, if the entangled polymer composition is a gel, the solvent typically has a low viscosity, so that the fully swollen gel has low interchain friction, further increasing elasticity.
In some embodiments, the stress-stretch curves of entangled polymer compositions exhibit negligible hysteresis. In some embodiments, the hysteresis is the ratio of the dissipated energy (i.e., area between the load and unload curves) to the applied work (i.e., the area under the load curve). In some embodiments, a negligible hysteresis is a hysteresis of less than about 5%. In some embodiments, the hysteresis is less than about 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or the hysteresis is in any range bounded by any two values disclosed herein. In some embodiments, the hysteresis is less than about 5%. In some embodiments, the hysteresis is less than about 1%.
In some embodiments, the entangled polymer composition shows a high toughness. In some embodiments, the entangled polymer composition forms a fabric-like topology: the dense entanglements weave and the sparse crosslinks knot. Without being bound to any particular theory, it is believed that when such a polymer composition is stretched, tension is distributed along the long length of a chain and to many other entangled chains before the chain breaks, as well as to a few other chains through two crosslinks. Thus, when a single covalent bond breaks, the energy stored in many long chains dissipates, leading to a high toughness of the entangled polymer composition described herein. In some embodiments, the combination of sparse crosslinks and dense entanglements enables the entangled polymer composition described herein (e.g., the entangled hydrogel) to de-concentrate stress and amplify toughness. In some embodiments, due to the fabric-like topology, entangled polymer compositions have both high toughness and high elasticity (negligible hysteresis), which is rare in polymers. In some embodiments, for polymers made from precursors of low C and I, crosslinks are sparse, and entanglements are dense, and toughness scales as Γ˜C−1/2, consistent with the prediction of the Lake-Thomas model. This confirms that entanglements do not hinder the transmission of tension along the length of the long polymer chains.
In some embodiments, the polymer composition has a toughness of at least about 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, or 1500 Jm−2, or the toughness is in any range bounded by any two values disclosed herein. In some embodiments, the toughness of an entangled polymer composition is between about 100 Jm−2 to about 2500 Jm−2. In some embodiments, the toughness of an entangled polymer composition is at least about 100 Jm−2. In some embodiments, the toughness of an entangled polymer composition is at least about 500 Jm−2. In some embodiments, the toughness is between about 100-200 Jm−2, 200-300 Jm−2, 300-400 Jm−2, 400-500 Jm−2, 500-600 Jm−2, 600-700 Jm−2, 600-700 Jm−2, 700-800 Jm−2, 800-900 Jm−2, 900-1000 Jm−2, 1000-1100 Jm−2, 1200-1300 Jm−2, 1300-1400 Jm−2, 1400-1500 Jm−2, 1500-1600 Jm−2, 1600-1700 Jm−2, 1700-1800 Jm−2, 1800-1900 Jm−2, or 1900-2000 Jm−2, or 2000-2500 Jm−2. In some embodiments, the entangled polymer composition is an entangled hydrogel, and the toughness of an entangled hydrogel is between about 100 Jm−2 and about 2000 Jm−2. In some embodiments, the entangled polymer composition is an entangled hydrogel which has a toughness of at least about 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, 1500, or 2000 Jm−2, or the toughness is in any range bounded by any two values disclosed herein. In some embodiments, the entangled polymer composition is an entangled elastomer which has a toughness between about 500 Jm−2 to about 2500 Jm−2. In some embodiments, the entangled elastomer has a toughness of at least about 500, 600, 700, 800, 900, 1000, 1200, 1500, or 2000 Jm−2, the toughness is in any range bounded by any two values disclosed herein.
As discussed above, in some embodiments, the entangled polymer compositions have both high stiffness and high toughness. In some embodiments, the entangled polymer compositions do not suffer from the stiffness-toughness conflict that exists in polymers that rely on crosslinks rather than entanglements, here called “crosslink-dominant polymers” to distinguish from the entangled polymer compositions described herein (entanglement-dominant polymers) which have a higher density of entanglements than crosslinks and rely primarily on entanglement rather than crosslinks.
In some embodiments, the entangled polymer composition has high toughness while also exhibiting negligible hysteresis. In many polymers, hysteresis and toughness are positively correlated. These properties measure energy dissipation in two ways. Hysteresis measures energy dissipated in loading and unloading a sample without crack propagation. Toughness measures energy dissipated in crack propagation. Indeed, such hysteresis-toughness correlation has been commonly stated as a design principle in developing tough polymers. In some embodiments, highly entangled polymer compositions are exceptional in that they break the hysteresis-toughness correlation and simultaneously achieve both low hysteresis and high toughness. In some embodiments, highly entangled hydrogels achieve high toughness not by sacrificial bonds, but by having long chains and entanglements that can distribute tension. In a polymer with sacrificial bonds, upon loading, the sacrificial bonds break and do not heal within a short time, resulting in irreversible deformation. Consequently, the polymer degrades and has a different stress-stretch curve upon reloading. If the polymer is submerged in water, to form a gel, the degraded gel swells more and becomes even weaker. These shortcomings do not appear in a highly entangled polymer compositions or hydrogels as described herein. In some embodiments, entangled polymer compositions can be loaded and unloaded repeatedly while deforming reversibly.
In some embodiments, entanglements contribute to the strength of entangled polymer compositions for several reasons. First, entanglements readily slip and enable tension to transmit in polymer chains along their lengths. Second, entanglements transmit tension between polymer chains, and a highly entangled polymer composition has many more entanglements than a crosslink-dominant polymer. When a crosslink-dominant polymer is stretched, chains break at different times due to statistical distribution, lowering the strength. In contrast, in an entangled polymer composition, the strength is increased when entanglements distribute tension both along a polymer chain and between polymer chains. Third, in gels swollen with solvent, entanglements constrain the swelling.
In some embodiments, the strength of the polymer composition is characterized by the nominal tensile strength. The nominal tensile strength is measured in tension and is the force at failure divided by the original cross-sectional area of the sample. In some embodiments, the polymer composition has a nominal tensile strength of at least about 100, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1500, 2000, 2500, 3000, or 3500 kPa, or the nominal tensile strength is in any range bounded by any two values disclosed herein. In some embodiments, the nominal tensile strength of an entangled polymer composition is at least about 100 kPa. In some embodiments, the nominal tensile strength of an entangled polymer composition is at least about 2 MPa. In some embodiments the nominal tensile strength of an entangled polymer composition is between about 100 kPa and 3.5 MPa. In some embodiments, the nominal tensile strength of an entangled polymer composition is 100-150 kPa, 150-200 kPa, 250-300 kPa, 300-350 kPa, 350-400 kPa, 400-450 kPa, 450-500 kPa, 500-600 kPa, 600-700 kPa, 700-800 kPa, 800-900 kPa, 900-1000 kPa, 1-1.5 MPa, 1.5-2 MPa, 2-2.5 MPa, 2.5-3.0 MPa, or 3.0-3.5 MPa. In some embodiments, the entangled polymer composition is an entangled hydrogel which has a nominal tensile strength between about 300-500 kPa. In some embodiments, the entangled hydrogel has a nominal tensile strength between about 300, 350, 400, 450, or 500 kPa or the nominal tensile strength is in any range bounded by any two values disclosed herein. In some embodiments, the nominal tensile strength of the entangled elastomer is between about 2.5-3.5 MPa. In some embodiments, the entangled polymer composition is an entangled elastomer which has a nominal tensile strength between about 2.5, 2.75, 3.0, 3.25, or 3.5 MPa, or the nominal tensile strength is in any range bounded by any two values disclosed herein.
In some embodiments, entanglements also improve the fatigue threshold of entangled polymer compositions subject to cyclical load. Performance of many polymers are limited, not by toughness under monotonic load, but by fatigue under cyclical load. For example, pure natural rubber has toughness ˜10−4 J/m2, but fatigue threshold ˜50 J/m2. The toughness of natural rubber comes mainly from a dissipation process in the bulk (i.e., strain-induced crystallization), and the fatigue threshold comes from breaking chains across the crack plane.
In some embodiments, the polymer composition has a fatigue threshold of at least about 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 300, or 350 Jm−2, or the fatigue threshold is in any range bounded by any two values disclosed herein. In some embodiments, the fatigue threshold of an entangled polymer composition is at least about 150 Jm−2. In some embodiments, the fatigue threshold of an entangled polymer composition is at least about 200 Jm−2. In some embodiments, the entangled polymer composition is an entangled hydrogel which has a fatigue threshold of at least about 200 Jm−2. In some embodiments, the entangled polymer composition is an entangled elastomer which has a fatigue threshold of at least about 240 Jm−2.
In some embodiments, the entangled polymer composition is an entangled gel infused with a solvent which is slippery and wear resistant. In some embodiment, the gel is infused with water and is a hydrogel. In some embodiments, the gel is infused with an organic solvent and is an organogel. In some embodiments, when a gel slides on a substrate, each polymer chain at the surface of the gel is anchored to the polymer network on one end, and mobile on the other end, provided that the polymer chain negligibly adsorbs to the substrate. These dangling and hydrophilic polymer chains stabilize a solvent-rich layer, which lubricates the surfaces. The friction decreases as the thickness of the solvent-rich layer increases, and the thickness scales with the size of the dangling chains. Highly entangled gels have much longer polymer chains than the crosslink-dominant gels, resulting in a lower friction coefficient.
In some embodiments, the polymer composition has a coefficient of friction of less than about 0.05, 0.04, 0.03, 0.02, 0.01, 0.005, or 0.001, or the coefficient of friction is in any range bounded by any two values disclosed herein. In some embodiments, the coefficient of friction of the entangled polymer composition is less than about 0.05. In some embodiments the coefficient of friction of the entangled polymer composition is less than about 0.04. In some embodiments, the coefficient of friction of the entangled polymer composition is less than about 0.03. In some embodiments, the coefficient of friction of the entangled polymer composition is less than about 0.02. In some embodiments the coefficient of friction of the entangled polymer composition is less than about 0.01. In some embodiments, the coefficient of friction of the entangled polymer composition is less than about 0.005. In some embodiments, the coefficient of friction of the entangled polymer composition is less than about 0.001. In some embodiments, the coefficient of friction of the entangled polymer composition is less than about 0.006-0.007.
In some embodiments, the wear rate of the entangled polymer composition is less than about 1, 0.5, 0.3, 0.25, 0.2, 0.15, or 0.1 mg/cycle, or the wear rate is in any range bounded by any two values disclosed herein. In some embodiments, the wear rate of the entangled polymer composition is less than about 0.1-0.2 mg/cycle.
In some embodiments, entangled polymer compositions include long chained polymers. By including long chained polymers, entangled polymer compositions can transmit tension along the lengths of those polymer chains, contributing to high toughness and low hysteresis. In some embodiments, the molecular weight of the polymer chains in the entangled polymer composition is at least about 5×105 g/mol or at least about 106 g/mol, or any range bounded by any two values disclosed herein.
Non-limiting exemplary polymers include natural rubber, silicon rubber, poly(ethyl acrylate), poly(acrylamide), polyacrylic acid, polyethylene glycol, polyvinylpyrrolidone, polyvinyl alcohol, poly(2-hydroxyethyl methacrylate), poly(methacrylic acid), poly(N-isopropyl acrylamide), poly(methyl methacrylate), polymethacrylate, poly(ethyl methacrylate), poly(propyl acrylate), poly(propyl methacrylate), poly(butyl acrylate), poly(methacrylic acid), poly(butyl methacrylate), polyethylene, polypropylene, poly(vinyl acetate), polyacrylonitrile, polybutadiene, polyisobutylene, polyisoprene, polychloroprene, polynorbornene, polytetrafluoroethylene, ethylene acrylate copolymers, poly(ethylene-co-acrylic acid), poly(ethylene-co-ethyl acrylate), poly(ethylene-co-methacrylic acid), poly(ethylene-co-vinyl acetate), poly(acrylonitrile-co-butadiene), poly(isobutylene-co-isoprene), poly(perfluoromethylvinylether), poly(styrene-co-butadiene), polyurethane, polysulfide, polysiloxane, and any combinations or copolymers thereof. Non-limiting exemplary polymers include cellulose, alginate, chitosan, hyaluronic acid, collagen, gelatin, starch, chitin, agarose, dextran, konjac glucomannan, pullulan, guar gum, polynucleotide, polyisoprene, polyamide, and a combination thereof.
In some embodiments, the entangled polymer composition is swollen with a solvent to form a gel. If the solvent is water, an entangled hydrogel is formed. If the solvent is an organic solvent, an entangled organogel is formed. Non-limiting exemplary organic solvents include ethylene glycol, glycerol, ethyl alcohol, isopropyl alcohol, tetrahydrofuran, silicone oils, dimethyl sulfoxide, dimethylformamide, and a combination thereof.
In some embodiments, the entangled polymer composition is an entangled hydrogel. Exemplary hydrogels include poly(acrylamide), poly acrylic acid, polyethylene glycol, cellulose, alginate, chitosan, hyaluronic acid, collagen, gelatin, starch, chitin, agarose, dextran, konjac glucomannan, and a combination thereof. In some embodiments, the hydrogel is a polyelectrolyte. Non-limiting exemplary polyelectrolytes include poly acrylic acid, polygalacturonic acid, alginic acid, carboxymethyl cellulose, poly(2-Acrylamido-2-methyl-1-propanesulfonic acid), poly(sodium p-styrenesulphonate), and poly(3-(methacryloylamino) propyl-trimethylammonium chloride), poly(methyl chloride quarternized N, N-dimethylamino ethylacrylate), and a combination thereof.
In some embodiments, the entangled polymer composition is an elastomer. Non-limiting exemplary elastomers include natural rubber, silicon rubber, poly(ethyl acrylate), poly(acrylamide), polyacrylic acid, poly(methyl methacrylate), polymethacrylate, poly(ethyl methacrylate), poly(propyl acrylate), poly(propyl methacrylate), poly(butyl acrylate), poly(acrylic acid), poly(methacrylic acid), poly(butyl methacrylate), polyethylene, polypropylene, poly(vinyl acetate), polyacrylonitrile, polybutadiene, polyisobutylene, polyisoprene, polychloroprene, polynorbornene, polytetrafluoroethylene, ethylene acrylate copolymers, ethylene acrylate copolymers, poly(ethylene-co-acrylic acid), poly(ethylene-co-ethyl acrylate), poly(ethylene-co-methacrylic acid), poly(ethylene-co-vinyl acetate), poly(acrylonitrile-co-butadiene), poly(isobutylene-co-isoprene), poly(perfluoromethylvinylether), poly(styrene-co-butadiene), polyurethane, polysulfide, polysiloxane, and any combinations or copolymers thereof.
In some embodiments, the entangled polymer composition is an organogel. In some embodiments, an organogel is an elastomer swollen with an organic solvent. Non-limiting exemplary organogels include poly(ethyl acrylate) swollen with dimethylformamide. In some embodiments the organogel is an elastomer selected from natural rubber, silicon rubber, poly(ethyl acrylate), poly(methyl methacrylate), polymethacrylate, poly(ethyl methacrylate), poly(propyl acrylate), poly(propyl methacrylate), poly(butyl acrylate), poly(acrylic acid), poly(methacrylic acid), poly(butyl methacrylate), polyethylene, polypropylene, poly(vinyl acetate), polyacrylonitrile, polybutadiene, polyisobutylene, polyisoprene, polychloroprene, polynorbornene, polytetrafluoroethylene, and any combinations or copolymers thereof, and the organic solvent is selected from ethylene glycol, glycerol, ethyl alcohol, isopropyl alcohol, tetrahydrofuran, silicone oils, dimethyl sulfoxide, dimethylformamide, and a combination thereof.
In some embodiments, the entangled polymer composition includes a small number of crosslinks. In some embodiments, the number of entanglements greatly outnumbers the number of crosslinks. For example, entangled polymer compositions can have about 100 entanglements between each crosslink. In some embodiments, entangled polymer compositions have about 50-100 entanglements per crosslink, 100-200 entanglements per crosslink, or 200-300 entanglements per crosslink. The number of crosslinks in entangled polymer compositions can also be expressed in terms of the density of crosslinks per monomer unit. In some embodiments, the density of crosslinks is no more than one crosslink per 1,000 monomer units of the polymer. In some embodiments, the density of crosslinks is no more than one crosslink per 10,000 monomer units of the polymer. In some embodiments, the density of crosslinks is no more than one crosslink per 100,000 monomer units of the polymer. In some embodiments, the entangled polymer composition are formed using fewer than one crosslink for 100,000, 90,000, 80,000, 70,000, 60,000, 50,000, 40,000, 30,000, 20,000, 10,000, 9,000, 8,000, 7,000, 6,000, 5,000, 4,000, 3,000, 2,000, or 1,000 monomer units, or the number of monomer units is any range bounded by any two values disclosed herein. Alternatively, the number of crosslinks can expressed in terms of the crosslink fraction C, the crosslinker-to-monomer molar ratio. In some embodiments, the crosslink fraction is less than about 10−3, less than about 10−4, less than about 10−5, or less than about 10−6, or in any range bounded by any two values disclosed herein. In some embodiments, the entangled polymer composition is a hydrogel, and the crosslink fraction is less than about 10−3, less than about 10−4, or less than about 10−5 or in any range bounded by any two values disclosed herein. In some embodiments, the entangled polymer composition is an elastomer, and the crosslink fraction is less than about 10−3, less than about 10−4, less than about 10−5, less than about 10−6, or in any range bounded by any two values disclosed herein.
Non-limiting exemplary crosslinkers include poly(ethylene glycol) diacrylate, Tricyclo[5.2.1.02,6]decanedimethanol diacrylate, Ethylene glycol diacrylate, 1,4-Butanediol diacrylate, Poly(propylene glycol) diacrylate, Di(ethylene glycol) diacrylate, Bisphenol A ethoxylate diacrylate, 1,3-Butanediol diacrylate, 1,6-Hexanediol diacrylate, Tri (ethyleneglycol) diacrylate, Neopentyl glycol diacrylate, Tetra(ethylene glycol) diacrylate, benzophenone, glycidyl methacrylate, adipic acid dihydrazide, butanediol-diglycidyl ether, citric acid, glutaraldehyde, divinyl sulfone, sulfur, and a combination thereof. In some embodiments, crosslinks can be formed by application of heat, UV (ultraviolet) light, visible light, gamma rays, catalysts, and a combination thereof.
A. Forming Entangled Polymer Compositions from Monomers
In another aspect, a method of forming an entangled polymer composition is disclosed, including a) providing a mixture including a plurality of monomers; a plurality of crosslinkers, wherein there are no more than one crosslinker per 1,000 monomers; and a solvent, wherein the molar ratio of solvent to monomer is less than 12; b) polymerizing the monomers to form polymers and entangling the polymers to form an entangled polymer network; and c) forming crosslinks by crosslinking the polymers. In some embodiments, the entangled polymer composition is synthesized from monomers. In these embodiments, entangled polymer composition is formed using monomers and low levels of other precursors including solvent, crosslinkers, and initiators. In some embodiments, the solvent is water. In some embodiments, the solvent is an organic solvent, e.g., ethylene glycol, glycerol, ethyl alcohol, isopropyl alcohol, tetrahydrofuran, silicone oils, dimethyl sulfoxide, dimethylformamide, and a combination thereof. In some embodiments, crowding monomers in a small amount of solvent results in crowded polymers which form dense entanglements. In these embodiments, monomers are mixed with a small amount of solvent and crosslinkers. The monomers are polymerized to form an entangled polymer network. In some embodiments, the precursors include an initiator to initiate polymerization. Crosslinks are formed in the polymer network, for example, by applying heat or UV light. In some embodiments, crosslinkers are formed at a density of no more than one crosslink per 1,000 monomers, no more than one crosslink per 10,000 monomers, or no more than one crosslink per 100,000 monomers. In some embodiments, the ratio of solvent to monomers is between about 0.0 and 12.0, for example about 0.0, 1.0, 2.0, 3.0, 3.2, 4.0, 5.0, 6.0, 7.0, 7.7, 8.0, 9.0, 10.0, 11.0 or 12.
In one embodiment, a method of forming an entangled polymer composition is disclosed, including a) providing a mixture including a plurality of monomers; a plurality of crosslinkers, wherein there are no more than one crosslinker per 1,000 monomers; and a solvent, wherein the molar ratio of solvent to monomer is less than 12; b) polymerizing the monomers to form polymers and entangling the polymers to form an entangled polymer network; c) forming crosslinks by crosslinking the polymer and; d) swelling the entangled polymer network with a solvent after forming crosslinks. In some embodiments, the solvent is water and the polymer composition is a hydrogel. In some embodiments, the solvent is an organic solvent and the polymer composition is an organogel.
The properties of entangled polymer compositions can be tuned based on synthesis parameters. In the precursor, let W be the solvent-to-monomer molar ratio, C be the crosslinker-to-monomer molar ratio, and/be the initiator-to-monomer molar ratio.
In
In
In some embodiments, the polymer network is swollen with a solvent after synthesis until reaching equilibrium. For example,
In some embodiments, elastomers can be formed using a monomer without solvent at low C and I. In some embodiments, monomers for entangled elastomers are selected based on the following considerations: i) the monomer is a liquid of low viscosity (e.g., 0.1 mP s˜100 mP s), (ii) the resulting polymer is rubbery (e.g., Tg<temperature), and (iii) the resulting polymer has low entanglement molecular weight (e.g., less than 103 g/mol) as measured by a rheometer. Non-limiting exemplary suitable monomers for entangled elastomers include ethyl acrylate, methyl methacrylate, methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, acrylic acid, methacrylic acid, butyl methacrylate, ethylene, propylene, vinyl acetate, acrylonitrile, butadiene, Isobutylene, isoprene, chloroprene, norbornene, tetrafluoroethylene, and combinations thereof.
In some embodiments, the solvent fraction W is between about 0.0 and 12.0, for example, about 0.0, 1.0, 2.0, 3.0, 3.2, 4.0, 5.0, 6.0, 7.0, 7.7, 8.0, 9.0, 10.0, 11.0 or 12, or the solvent ratio is in aby range bounded by any two values disclosed herein. In some embodiments, the solvent fraction W is equal to the lowest solubility of the monomer in the solvent. In some embodiments, the solvent fraction W s greater than about the lowest solubility of monomer in the solvent. In some embodiments, the solubility of the solvent is determined at 30° C.
As used herein, “initiator fraction” I refers to the molar ratio of initiator to monomer. In some embodiments, the initiator fraction I is 4.0×10−6, 8.0×10−6, or 8.0×10−5, or in any range bounded by any two values disclosed herein. In some embodiments, the initiator fraction is less than about 10−5.
As used herein, “crosslink fraction” C refers to the molar ratio of crosslinker to monomer. In some embodiments, the crosslink fraction C is about 3.2×10−6, 1.0×10−5, 1.0×10−4, or 1.0×10−3, or in any range bounded by any two values disclosed herein. In some embodiments, the crosslink fraction is less than about 10−3, less than about 10−4, less than about 10−5, or less than about 10−6, or in any range bounded by any two values disclosed herein.
In some embodiments the initiator to crosslinker ratio is 0.008, 0.08, 0.4, 0.5 or 0.8, 1.0 or in any range bounded by any two values disclosed herein. In some embodiments, the initiator to crosslinker ratio is less than 0.5. In some embodiments, the initiator to crosslinker ratio is less than 0.8. In some embodiments, the initiator to crosslinker ratio is less than 1.0.
In some embodiments, an entangled hydrogel is formed with W is about 2, C is about 1.2×10−5, I is about 4.8×10−6. In some embodiments, an entangled hydrogel is formed with W is about 0, C is about 1×10−6, I is about 1×10−6.
Non-limiting exemplary monomers include ethyl acrylate, acrylamide, acrylic acid, 2-Hydroxyethyl methacrylate, ethylene glycol, methacrylic acid, N-isopropyl Acrylamide, methyl methacrylate, methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, acrylic acid, methacrylic acid, butyl methacrylate, ethylene, propylene, vinyl acetate, acrylonitrile, butadiene, Isobutylene, isoprene, chloroprene, norbornene, tetrafluoroethylene, and a combination thereof.
Non-limiting exemplary initiators include 2-Hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone, 2-Hydroxy-2-methylpropiophenone, glycidyl methacrylate, 2-oxoglutaric acid, benzophenone, and a combination thereof.
Non-limiting exemplary crosslinkers include is poly(ethylene glycol) diacrylate, Tricyclo[5.2.1.02,6]decanedimethanol diacrylate, Ethylene glycol diacrylate, 1,4-Butanediol diacrylate, Poly(propylene glycol) diacrylate, Di(ethylene glycol) diacrylate, Bisphenol A ethoxylate diacrylate, 1,3-Butanediol diacrylate, 1,6-Hexanediol diacrylate, Tri (ethyleneglycol) diacrylate, Neopentyl glycol diacrylate, Tetra(ethylene glycol) diacrylate, benzophenone, glycidyl methacrylate, adipic acid dihydrazide, butanediol-diglycidyl ether, citric acid, glutaraldehyde, divinyl sulfone, sulfur, and a combination thereof. In some embodiments, the crosslinks are formed by application of heat, ultraviolet light, visible light, gamma rays, catalysts, and a combination thereof.
In some embodiments, the concentration of the oxygen dissolved in the precursor is as low as possible. For example, oxygen level in the curing environment should be as low as possible.
B. Forming Entangled Polymer Compositions from Preformed Polymers
In yet another aspect, a method of forming an entangled polymer composition is disclosed, including a) providing a mixture including a plurality of polymer chains; a plurality of crosslinkers, wherein there are no more than one crosslinker per 1,000 monomers in the polymer chains; and a solvent; b) kneading the mixture of precursors at a temperature of at least about 40° C. to form an entangled polymer network; and c) crosslinking the polymer chains to form crosslinks. In some embodiments, the method described herein can be described with reference to
In one embodiment, a method of forming an entangled polymer composition is disclosed, including a) providing a mixture including a plurality of polymer chains; a plurality of crosslinkers, wherein there are no more than one crosslinker per 1,000 monomers in the polymer chains; and a solvent; b) kneading the mixture of precursors at a temperature of at least about 40° C. to form an entangled polymer network; c) crosslinking the polymer chains to form crosslinks; In some embodiments, the solvent is water and the polymer composition is a hydrogel; and d) swelling the entangled polymer network with a solvent after forming crosslinks. In some embodiments, the solvent is an organic solvent and the polymer composition is an organogel.
In some embodiments, the dough is homogenized by kneading and annealing, such that the polymer chains do not degrade or break, but densely entangle. In some embodiments, kneading, annealing, or both occur at elevated temperatures. The polymer chains are then sparsely crosslinked. In some embodiments, the dough is swollen into a gel. In the entangled polymer composition formed from dough, the dense entanglements weave and the sparse crosslinks knot. Together, dense crosslinks and sparse crosslinks maintain the fabric-like topology in the polymer. When the entangled polymer composition is stretched, before a chain breaks, the tension transmits in the chain along its long length, and to many entangled chains and a few crosslinked chains. This de-concentration of tension strengthens and toughens the entangled polymer composition. In some embodiments, the entangled polymer composition shows high elasticity and high toughness simultaneously, because toughness does not come from sacrificial bonds but from having long chains. In some embodiments, the entangled polymer composition is further swelled by water to form an entangled hydrogel formed by this method is swell-resistant and has low friction. The method of forming entangled polymer compositions from doughs is generally applicable to synthetic and natural polymers, and is compatible with industrial processing technologies, opening doors to the development of sustainable, high-performance entangled polymer compositions and hydrogels.
Forming entangled polymer compositions from existing polymer chains by forming a dough has two benefits. First, some synthetic polymers require specialized polymerization conditions to achieve high molecular weight and low polydispersity. Such non-limiting exemplary synthetic polymers include poly(ethylene glycol), poly(vinyl pyrrolidone), poly(vinyl alcohol), silicone rubbers, nitrile rubbers, poly(methyl methacrylate), polymethacrylate, poly(ethyl acrylate), poly(ethyl methacrylate), poly(propyl acrylate), poly(propyl methacrylate), poly(butyl acrylate), poly(acrylic acid), poly(methacrylic acid), poly(butyl methacrylate), ethylene acrylate copolymers, poly(ethylene-co-acrylic acid), poly(ethylene-co-ethyl acrylate), poly(ethylene-co-methacrylic acid), poly(ethylene-co-vinyl acetate), poly(acrylonitrile-co-butadiene), polyacrylonitrile, polyisobutylene, poly(isobutylene-co-isoprene), poly(tetrafluoro ethylene), poly(tetrafluoroethylene), poly(perfluoromethylvinylether), poly(styrene-co-butadiene), polyurethane, polyisoprene, polychloroprene, polybutadiene, polysulfide, polynorbornene, polysiloxane, polyethylene, polypropylene, and combinations thereof. Second, many sustainable polymers are derived from natural polymers. Such non-limiting exemplary natural polymers include cellulose, alginate, chitosan, hyaluronic acid, collagen, gelatin, starch, chitin, agarose, dextran, konjac glucomannan, pullulan, guar gum, polynucleotide, polyisoprene, polyamide, and combinations thereof. As such, the method disclosed herein can efficiently utilize preformed or presynthesized polymer material.
As shown in an exemplary embodiment in
In contrast, when a polymer is formed using short-chain polymers, as shown in
In some embodiments, to form an entangled polymer composition from a dough, long polymer chains with high molecular weight are mixed with a solvent and crosslinker. In some embodiments, resulting mixture is an inhomogeneous and opaque dough. In some embodiments, the dough is homogenized by kneading, as shown in
In some embodiments, the properties of entangled polymer compositions made from doughs depend on various synthesis parameters, including the initial polymer fraction φi (the mass ratio of polymer to the dough), the crosslink fraction B (the molar ratio of crosslinker to monomer unit of the polymer), and molecular weight of the polymer Mv. In the examples shown in
This molecular interpretation is corroborated by elastic modulus E of the equilibrium hydrogels plotted as a function of B and φi at Mv=8×106, shown in
In some embodiments, the polymers used to form an entangled polymer composition from a dough are synthetic polymers. Non-limiting exemplary synthetic polymers include poly(ethylene glycol), poly(vinyl pyrrolidone), poly(vinyl alcohol), poly(2-hydroxyethyl methacrylate), poly(N-isopropyl acrylamide), silicone rubbers, nitrile rubbers, poly(methyl methacrylate), polymethacrylate, poly(ethyl acrylate), poly(acrylamide), poly(ethyl methacrylate), poly(propyl acrylate), poly(propyl methacrylate), poly(butyl acrylate), poly(acrylic acid), poly(methacrylic acid), poly(butyl methacrylate), ethylene acrylate copolymers, poly(ethylene-co-acrylic acid), poly(ethylene-co-ethyl acrylate), poly(ethylene-co-methacrylic acid), poly(ethylene-co-vinyl acetate), poly(acrylonitrile-co-butadiene), polyacrylonitrile, polyisobutylene, poly(isobutylene-co-isoprene), poly(tetrafluoro ethylene), poly(tetrafluoroethylene), poly(perfluoromethylvinylether), poly(styrene-co-butadiene), polyurethane, polyisoprene, polychloroprene, polybutadiene, polysulfide, polynorbornene, polysiloxane, polyethylene, polypropylene, poly(vinyl acetate), and a combination thereof. In some embodiments, the polymers used to form an entangled polymer composition from a dough are natural polymers. Non-limiting exemplary natural polymers include cellulose, alginate, chitosan, hyaluronic acid, collagen, gelatin, starch, chitin, agarose, dextran, konjac glucomannan, pullulan, guar gum, polynucleotide, polyisoprene, polyamide, and a combination thereof.
In some embodiments, the polymers used to form an entangled polymer composition from a dough have a molecular weight of at least about 5×105, 106, 5×106 g/mol, or any range bounded by any two values disclosed herein.
Non-limiting exemplary crosslinkers include benzophenone, glycidyl methacrylate, glyoxal, oxidized dextrin, epichlorohydrin, adipic acid dihydrazide, endogen polyamine spermidine, ethylene glycol dimethacrylate, butanediol-diglycidyl ether, citric acid, glutaraldehyde, divinyl sulfone, sulfur, and any combination thereof. Crosslinks can be formed by application of heat, UV light, visible light, gamma rays, catalysts, and any combination thereof.
In some embodiments, the mixture (e.g., a dough) is formed using polymer chains and a small amount of solvent. In some embodiments, using a small amount of solvent leads to crowding and entanglement of the polymer chains. In some embodiments, the initial polymer fraction φi in the mixture is at least about 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% by mass, or any range bounded by any two values disclosed herein. In some embodiments, the initial polymer fraction in the mixture is at least about 45% by mass. In some embodiments, the initial polymer fraction in the mixture is least about 60% by mass. In some embodiments, the initial polymer fraction in the mixture is between about 60% and about 75% by mass. In some embodiments, the solvent fraction in the mixture is less than about 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, or 5%, 4%, 3%, 2%, or 1% by mass. In some embodiments, the solvent fraction in the mixture is less than about 55% by mass. In some embodiments, the solvent fraction in the mixture is less than about 40% by mass. In some embodiments, the solvent fraction in the mixture is between about 25% and about 40% by mass.
In some embodiments, the dough used to form entangled polymer compositions includes long chained polymers. By including long chained polymers, entangled polymer compositions can transmit tension along the lengths of those polymer chains, contributing to high toughness and low hysteresis. In some embodiments, the molecular weight of the polymer chains in the dough is at least about 5×105 g/mol, at least about 106 g/mol, or at least about 5×106 g/mol, or any range bounded by any two values disclosed herein.
In some embodiments the dough is kneaded for between about 3 and 10 cycles, for example 3, 4, 5, 6, 7, 8, 9,10, 15, or 20 cycles, or in any range bounded by any two values disclosed herein. In some embodiments, the dough is kneaded at an elevated temperature. In some embodiments, the dough is kneaded at a temperature of at least about 40° C. In some embodiments, the dough is kneaded at a temperature of at least about 60° C. In some embodiments, the dough is kneaded at a temperature of at least about 40° C., 50° C., 60° C., 70° C., 80° C., 90° C., 100° C., 110° C., 120° C. or at any range bounded by any two values disclosed herein. In some embodiments, the kneading temperature is increased if the kneading time is short. In some embodiments, the dough is kneaded at a stretch rate of less than about 1×10−2 s−1.
In some embodiments, the dough is annealed at an elevated temperature after crosslinking. In some embodiments, the dough is annealed at a temperature of at least about 50° C., 60° C., 65° C., 70° C., 75° C., 80° C., 85° C., 90° C., or 95° C., 100° C., 110° C., 120° C. or at any range bounded by any two values disclosed herein. In some embodiments, the dough is annealed at between about 65° C. and about 95° C., for example 65° C., 80° C., or 95° C. In some embodiments, the dough is annealed at 65-70° C., 70-75° C., 75-80° C., 80-85° C., 85-90° C., or 90-95° C., or at any range bounded by any two values disclosed herein. In some embodiments, the dough is annealed for at least about 3, 6, 9, 12, or 15 hours, or for any range bounded by any two values disclosed herein. In some embodiments, the dough is annealed for between about 3 hours and about 15 hours, for example, 3-6 hours, 6-9 hours, 9-12 hours, or 12-15 hours. In some embodiments, the annealing time depends on the annealing temperature. In some embodiments, the annealing time and temperature are limited to avoid degradation of the polymer.
In some embodiments, the dough becomes annealed during the kneading process. In these embodiments, dough need not be annealed for a specific time or at a specific temperature after kneading.
In some embodiments, the dough is swollen with a solvent after crosslinking to form a gel. Non-limiting exemplary solvents include water, ethylene glycol, glycerol, ethyl alcohol, isopropyl alcohol, tetrahydrofuran, silicone oils, dimethyl sulfoxide, dimethylformamide, and combinations thereof.
Certain embodiments will now be described in the following non-limiting examples.
Acrylamide (AAm, A8887), N,N′-methylenebisacrylamide (MBAA, M7279), and 2-Hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure 2959, 410896) were used as a monomer, crosslinker, and photo-initiator. They were purchased from Sigma Aldrich and used as received. Deionized water was used as a solvent and purchased from Poland Spring. 30 g of acrylamide and 15 mL of water were mixed to make a monomer solution. 0.1 M of crosslinker solution was prepared with water. 0.1 M of initiator solution was prepared with ethanol. The solutions of monomer, crosslinker, and initiator were mixed with additional water in a conical tube to make a precursor of specific values of W, C, and I. For high C, the crosslinker and the initiator were mixed without diluting. The mixture was vortexed for 5 seconds. To remove dissolved gas, the precursor was sonicated under 30° C. for 3 minutes. Molds were made of polytetrafluoroethylene (PTFE) sheets (8569K47), acrylic sheets (8560k355), and glass plates (8476K15) as a spacer, substrate, and cover, respectively. Molds were cut by using a laser cutter (Helix 75W, Epilog Laser). All engineering materials were purchased from McMaster-Carr. The spacer was put on the substrate without adhesives. The precursor was poured onto the mold and sealed with the cover. The substrate and the cover were tightly fixed by binder clips. UV light (8 ea, Sankyo Denki, F8T5BL) was irradiated for 3 hours with an intensity of 1.5 mW/cm2. After curing, the sample was weighed and submerged in water for more than 1 day to swell to equilibrium. The fully swollen sample was weighed again to measure the swelling ratio, R. The thickness of the fully swollen sample was calculated by multiplying R1/3 to the as-synthesized thickness. The polymer content φ was calculated by R−1(1+WMWaterMAAm−1)−1, where M is the molecular weight. For the samples shown in
As shown in
As shown in
Entanglements also markedly strengthen polymers, as illustrated in
The friction coefficient was measured by a rheometer (ARES-G2, TA Instrument), shown in the inset of
The wear rate was measured by a homemade setup, shown in the inset of
D. Synthesis of Highly Entangled Hydrogels at W Values Lower than 2
The value W=2.0 is the lowest allowed by the solubility of acrylamide in water of 30° C. The melting temperature of pure acrylamide is 84° C., and the glass transition temperature of dry polyacrylamide is 165° C. The extreme condition of W=0 was attempted by putting pure acrylamide into a tube and placing it in thermal contact with boiling water (100° C.). The acrylamide polymerizes without an initiator, and the product is glassy and inhomogeneous. Precursors of W=1.15 and various values of C were also attempted. After synthesis and swell in water to equilibrium, the hydrogels are squishy and translucent. At C=1×10−5, φ is about four times lower than that of W=2.0. The glassy phase during synthesis may have retarded polymerization.
Let W, C, and I be the molar ratios of solvent, crosslinker, and initiator to monomer. After synthesis, each polyacrylamide hydrogel was submerged in water to swell to equilibrium and then characterized by various tests.
Swelling of an entangled acrylamide hydrogel was observed over time. After synthesis, the hydrogel was submerged in water and weighed at various times. The swelling ratio over time is shown in
The effect of crosslink fraction on swelling ratio was investigated. Each hydrogel was synthesized using a precursor of specific values of W and C. The as-synthesized polyacrylamide hydrogel was submerged in water to swell to equilibrium. The swelling ratio was measured as the ratio of the mass of the fully swollen hydrogel to that of the as-synthesized hydrogel.
G. Hysteresis of as-Prepared Entangled Hydrogels
The storage and loss modulus of entangled polyacrylamide hydrogels were measured by a rheometer (ARES-G2, TA Instrument). The diameter of the top stage was 25 mm. The thickness of the fully swollen highly entangled hydrogel was 1.3 mm. The hydrogel was cut into a circle with the diameter of 25 mm. The bottom surface was glued onto the rheometer, and the top surface was not. An axial force of ˜1 N was applied, and the storage and loss modulus were measured as a function of frequency. The materials were submerged in water during the experiment.
A highly entangled hydrogel made of polyacrylamide and a double-network hydrogel made of polyacrylamide and alginate were prepared. The highly entangled hydrogel was prepared as described above. The double-network hydrogel was made of acrylamide and alginate (FMC Corporation). The water content was 86% by weight and the weight ratio between acrylamide and alginate was 3:1. The amount of the covalent crosslinker, N,N′-Methylenebisacrylamide (MBAA), was 0.003% of acrylamide (AAm) by weight, and the amount of the physical crosslinker, CaSO4 (Sigma-Aldrich, C3771), was 0.13% of alginate by weight. 1.5 μL of the 0.1 M initiator solution was added per 1 mL of the precursor. After mixing, the precursor was cured with the same procedure used for highly entangled hydrogels. The double-network hydrogel was used without swelling.
In the double-network hydrogel, one network has pre-stretched short chains, and the other has stretchable long chains. When such a double-network is subjected to a small stretch, both networks do not break, and the short-chain network stiffens the material. With increasing stretch, the short-chain network will break at isolated spots (e.g., sacrificial bonds), while the long-chain network transmits stress and elicits many other short chains to break. The distributed scission toughens the material, but, as discussed below, also causes pronounced hysteresis and inelasticity.
The highly entangled hydrogel and the double-network hydrogel of the similar polymer content of ˜15% were loaded with a weight of 5 N and then plucked. The dimension of each hydrogel before loading is 53 mm×35 mm×1.3 mm. The load cell connected to the hydrogel measures the load in time.
A metal ball was dropped onto the ˜4 mm-thick highly entangled hydrogel and the double-network hydrogel.
A polyacrylic acid hydrogel was synthesized with a precursor of W=2.0, C=1×10−5, and I/C=0.4, and submerged in pure water to swell to equilibrium.
Ethyl acrylate (EA, E9706), Tricyclo[5.2.1.02,6]decanedimethanol diacrylate (TDDA, 496669), 2-Hydroxy-2-methylpropiophenone (Irgacure 1173, 405655), and N,N-Dimethylformamide (DMF, 227056) were used as a monomer, crosslinker, photo-initiator, and solvent. These materials were purchased from Sigma Aldrich and used as received. Photo-initiator (PI) and TDDA in were dissolved in DMF respectively, and made into solutions of 1% in weight for the convenience of further use. The highly entangled elastomers were synthesized by photopolymerization. The monomer, crosslinker solution, and initiator solution were mixed in a conical tube to make a precursor of specific values of W, C, and I. I/C was set to 0.1 for the experiments shown in
The grippers for mechanical testing of entangled elastomers were made of acrylic sheets (8560K172). A sample of elastomer was cut into a rectangular shape with 70 mm×40 mm. An adhesion promoter (Loctite 7701™) was first sprayed on both sides of the sample, and the solvent of the promoter was allowed to evaporate for three minutes. Then, the sample was glued with the grippers using an adhesive (Loctite 406™) and loaded to the Instron 5966. In the undeformed state, the stretchable part of each sample was 70 mm×10 mm. The thickness of the sample was 0.67 mm. In measuring stiffness, hysteresis, and toughness, the loading rate was ˜0.1 s−1. In measuring the strength, the elastomer was cut into a dumbbell shape (ISO 37-2), and the loading rate was ˜0.1 s−1. In measuring the fatigue threshold, the crack advance was measured after 20,000 cycles.
A. Synthesis of Entangled Hydrogels from Dough of Long-Chain PEG Polymers
Polyethylene glycol (PEG) was used as a model polymer. A dough was made by mixing long-chain PEG with a small amount of water and benzophenone. In the dough, the long polymers are crowded but mobile, so that the long polymers densely entangle. UV light is applied, and benzophenone functions as a photoinitiator to create free radicals on the PEG chains, so that the polymers sparsely crosslink. The dough was submerged in water to swell to equilibrium. PEG hydrogels were formed using PEG polymers of with the following molecular weights: 200,000, 600,000, 2,000,000, and 8,000,000.
The highly entangled PEG hydrogels were prepared in following steps: mix, knead, anneal, crosslink, and swell. As the amount of benzophenone was small, it was first dissolved in 1.2 g of isopropyl alcohol, and then 2.5 g of PEG powder was mixed with the benzophenone solution by stirring for 2 min. The mixture was left in an oven at 65° C. for 15 min to evaporate the isopropyl alcohol. Then the powders of PEG and benzophenone were roughly mixed with water to form a dough. The dough was initially inhomogeneous and opaque, as shown in
To homogenize the dough, it was kneaded at an elevated temperature. The dough was put between a pair of aluminum plates (McMaster-Carr 1655T8) with a 0.5 mm-thick polyethylene spacer. The plates were compressed by using eight C-shaped clamps (McMaster-Carr 5133A13) in 2 min, and held for 9 min, all at 80° C. in the oven. The dough slowly became a thin film with the thickness of the spacer. Then, the dough was folded twice, once horizontally and once vertically, as shown in
The homogenized dough was crosslinked for 1.3 h under UV irradiation (˜15 mW/cm2, 365 nm, 15W, UVP XX-15L) in a nitrogen environment.
During knead, anneal, and crosslink steps, the dough was kept in a plastic bag (reclosable zip bag) to prevent drying. The crosslinked dough was swollen in water for one day to reach equilibrium.
The highly entangled PEG hydrogel used in
B. Synthesis of Crosslink-Dominant Hydrogels from Short-Chain PEG Polymers
A short-chain hydrogel with net-like topology was synthesized to contrast with the fabric-like topology of the entangled hydrogel formed from a dough of long-chain polymers. The short-chain hydrogel was synthesized from poly(ethylene glycol) diacrylate (PEGDA) of low molecular weight of 7×102 g/mol. A precursor consisting of 20 wt % of PEGDA, 0.02 wt % of Irgacure 2959, and 80 wt % water was prepared. As shown in
The short-chain PEG hydrogel and entangled PEG hydrogel were compared using various mechanical tests.
As shown in
As shown in
As shown in the stress-stretch curves in
The properties of entangled PEG hydrogels made from doughs depend on various synthesis parameters, including the initial polymer fraction φi (the mass ratio of polymer to the dough), the benzophenone fraction B (the molar ratio of benzophenone to monomer unit of the polymer), and molecular weight of the polymer Mv. Each dough was homogenized and crosslinked, and then submerged in water to form an equilibrium hydrogel. When B, φi and Mv are low, the dough dissolves in water. When B, φi and Mv exceed critical conditions, the dough gels and swells to equilibrium. In either case, let of be the final mass fraction of polymer in the equilibrated sample.
As shown in
The conditions of mixing, kneading, and annealing are determined based on the physics and chemistry of PEG. Dry long-chain PEG is semicrystalline, which melts at ˜65° C., dissolves in a large amount of water, and degrades over time at elevated temperature.
The dry powder remains powdery after being kept at elevated temperature overnight.
PEG degrades substantially when kept at elevated temperature for too long. The PEG with a small amount of water remains powdery after kneading at room temperature. The PEG turns into a translucent dough with kneading at elevated temperature. To homogenize a dough without degradation and scission, kneading must operate in a window of temperature, time, and rate of deformation, and annealing must operate in a window of temperature and time. Mixing the powder with a small amount of water lowers viscosity and eases homogenization.
Highly entangled hydrogels were prepared using long-chain 2-hydroxyethyl cellulose. The 2-hydroxyethyl cellulose is modified from naturally existing cellulose, forms fewer hydrogen bonds than native cellulose, and dissolves in water. A dough was prepared from long-chain 2-hydroxyethyl cellulose (Mv˜1.3×106), homogenized by kneading at 80° C., crosslinked using glycidyl methacrylate (GMA)47 and Irgacure 2959, and swollen in water to form an equilibrium hydrogel. To prepare entangled cellulose hydrogels, a HCl solution with a pH value of 3.5 was prepared. 0.1 mL of glycidyl methacrylate (GMA) and 20 mg of Irgacure 2959 were dissolved in 3 mL of the HCl solution. This solution was mixed with 2 g of 2-hydroxyethyl cellulose and rested it at 25° C. for 1 hour to obtain a cellulose dough. The dough was compressed by using a pair of aluminum plates, a 0.5 mm-thick polyethylene spacer, and eight C-shaped clamps, and store it in an oven at 80° C. for 15 min. The dough was annealed at 50° C. for 24 h. After annealing, the dough was cured for 20 min under UV irradiation. During all processes, the dough was kept in a plastic bag to prevent drying. Before any measurement, the hydrogels were swollen in water for one day to reach equilibrium.
The resulting entangled cellulose hydrogel had a final polymer fraction of of 20%. As shown in
The mechanical properties of entangled cellulose hydrogels were measured as described above for PEG hydrogels and are shown in
It will be appreciated that while one or more particular materials or steps have been shown and described for purposes of explanation, the materials or steps may be varied in certain respects, or materials or steps may be combined, while still obtaining the desired outcome. Additionally, modifications to the disclosed embodiment and the invention as claimed are possible and within the scope of this disclosed invention.
The present application claims priority to and the benefit of the earlier filing date of U.S. Patent Application No. 63/247,587, filed on Sep. 23, 2021, and entitled “Entangled Polymer Networks,” the content of which is hereby incorporated by reference herein in its entirety.
This invention was made with government support under 2011754 awarded by the National Science Foundation. The U.S. Government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2022/076834 | 9/22/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63247587 | Sep 2021 | US |
