Patent Application
20170145145
The disclosure generally provides high-molecular-weight thermoplastic polyester-based urethanes (TPEUs). In some embodiments, the component monomers of the TPEUs are entirely derived from renewable sources. The disclosure also provides methods of making high-molecular-weight TPEUs, and, in particular, methods for achieving such high molecular weights. The disclosure also provides certain uses of such TPEUs.
Segmented thermoplastic poly(ester urethane) (TPEU) elastomers are an interesting class of copolymers composed of a polyester macrodiol “soft segment” block and a “hard segment” block of urethane-rich segments formed by the reaction of a diisocyanate with a chain-extender diol. The polyester and urethane segments phase separate into nanoscale domains of crystalline “hard” segments which serve as a load bearing phase in the amorphous “soft” domains which provide extensibility. Segmented TPEUs are therefore two-phase polymers in contrast to one-phase polyurethanes synthesized without chain-extenders. TPEUs generally have excellent elastic properties and biocompatibility and generate a wide range of applications from wire and cable insulation jackets, automotive parts, footwear to biomedical devices where the hydrolytically labile polyester groups provide controlled degradation. Their chemical versatility allows for varying the type, ratio and processing conditions of starting components, to tailor the structure for customized applications.
Recently, the design of TPEU elastomers from vegetable oils have received much attention as potential substitutes that can compete with petroleum-based counterparts on a properties-function platform; with a positive environmental impact. However, the polyurethanes that are entirely derived from lipids so far presented low molecular weights and demonstrated inferior mechanical and elastic properties compared to those made partially from lipid—or fully from petroleum-based diols and diisocyanates. Also, the aliphatic fatty acid chains (12-22 carbons) of the triacylglycerol structure provide a shield for the ester groups, potentially delaying degradation.
Mechanical properties of high molecular weight polyurethane elastomers, associated with the hard and soft segment phase separation, have been shown to be a function of the monodisperse crystalline domains formed due to inter-segmental urethane-urethane hydrogen bonding. Moderate crystallinity arising from soft segments also introduces phase separation and reinforces mechanical strength. However, increased urethane-ester interaction, due to the presence of the proton acceptor carbonyl groups in polyester and urethane segments, increases phase mixing, adversely affecting tensile properties.
It has been shown through accelerated hydrothermal tests that hydrolytic ageing reduces molecular weight of TPEUs followed by the deterioration of mechanical and thermal properties. It has also been shown, in one embodiment, that aliphatic diisocyanates lack the cytotoxic degradation products associated with aromatic diisocyanate degradation and degrade into benign carboxylic acid by-products, especially useful for biomedical applications such as resorbable implants and scaffolds for tissue regeneration. Hydrolytic tests are sufficiently accelerated above 70° C. to allow for observable differences due to hydrolysis on structure and properties in a reasonable time, typically within 10-30 days. ASTM D3137 recommends a temperature of 85° C. for hydrolytic ageing tests. Tensile tests based on the modulus and elongation including the tensile half-life; which determines the time required for the tensile strength of the hydrolyzed polymer to reach half the tensile strength of the untreated polymer, have been widely used to rank the utility of hydrophilic polymers exposed to hydrolysis. Although these tests provide a measure of the macroscopic extent of polymer degradation, they do not inform on the pathways of degradation or the impact on the microstructure. Therefore, other methods such as 1H-NMR, FTIR, GPC, SEM, TGA and DSC are concurrently necessary to determine the impact on microstructure.
Thus, there is a continuing need to develop new approaches to making TPEUs that can overcome one or more of the aforementioned problems.
In the present disclosure, entirely lipid-derived segmented TPEUs with enhanced elastomeric properties have been prepared by improving urethane-urethane hydrogen bonding and phase separation, by optimization of the structure and distribution of the urethane hard segments. The effect of chain extender and polymerization protocol on the solubility, phase separation, and thermal and mechanical properties of segmented elastomers were compared to the one-phase TPEU elastomer prepared previously by the one-shot method without using chain extender. The second objective was to subsequently investigate the effect of hydrothermal ageing on the structure and thermal and mechanical properties of these lipid-derived segmented and one-phase TPEU elastomers.
In some embodiments, entirely lipid-derived thermoplastic TPEU elastomers prepared from oleic acid based polyester diols PEDs, 1,7-heptamethylene diisocyanate (HPDMI) and 1,9-nonanediol (ND) as chain extender were prepared following two different protocols (described in more detail below). One difference in these protocols is the timing of the addition of the chain extender. In some embodiments, the chain extender is added in a second step, where it reacts with a diisocyanate-terminated poly(ester urethane) prepolymer. In this disclosure, the TPEUs made by that protocol are identified as “ND-A.” In some other embodiments, the chain extender is added in a first step, where it reacts with the diisocyanate monomer to form a polycarbamate prepolymer. In this disclosure, the TPEUs made by that protocol are identified as “ND-B.”
The TPEUs of the present disclosure can have certain beneficial properties. In some embodiments, the disclosure provides rubber-like elastomeric TPEUs with low initial modulus of 49 MPa and maximum strain of 440% superior to all other entirely lipid-derived segmented TPEUs previously reported. In some embodiments, the disclosure provides TPEUs having maximum strain superior to entirely lipid-derived one-phase TPEUs prepared without chain extenders. In some embodiments, the disclosure provides TPEUs having enhanced hydrogen bond density and phase separation achieved by the control of hard segment sequence length and distribution via the use of a chain extender and customized polymerization protocols. In some embodiments, the disclosure provides solvent-resistant TPEUs, not soluble at room temperature and insoluble or partially soluble at the solvent boiling point, in a large range of polarity solvents such chloroform, tetrahydrofuran (THF), dimethylformamide (DMF), N-methyl-pyrrollidone (NMP), dimethylimidazolidinone (DMI) and dimethysulfoxide (DMSO); solvents commonly used for processing polyurethanes. In some embodiments, the disclosure provides TPEUs having glass transition temperatures and mechanical properties comparable to commercially available entirely petroleum-derived TPEUs and partially lipid-derived TPEUs previously reported.
In some embodiments, the disclosure provides lipid-derived segmented TPEUs having certain desirable hydrothermal ageing characteristics. In some embodiments, the disclosure provides TPEUs having molecular weight degradation after 15 days of immersion in water at 80° C.—a drop from 85,000 g/mol at 15 days to 10,000 g/mol at 30 days. In some other embodiments, the disclosure provides TPEUs having mechanical properties that deteriorate under accelerated hydrothermal ageing conditions demonstrating a tensile half-life within 1 day of immersion, rendering the TPEUs unable to withstand any tensile loads.
In a first aspect, the disclosure provides polymer compositions, comprising one or more urethane polymers formed from a first reaction mixture, which comprises chain-extending monomers and diisocyanate-terminated poly(ester urethane) prepolymers; wherein the diisocyanate-terminated poly(ester urethane) prepolymers are formed from a second reaction mixture, which comprises C2-40 diisocyanates and dihydroxyl-terminated polyesters; and wherein the dihydroxyl-terminated polyesters are formed from a third reaction mixture, which comprises C9-22 diols and C7-22 dicarboxylic acids or esters thereof.
In a second aspect, the disclosure provides polymer compositions, comprising one or more urethane polymers formed from a first reaction mixture, which comprises diisocyanate-terminated polycarbamate prepolymers and dihydroxyl-terminated polyesters; wherein the diisocyanate-terminated polycarbamate prepolymers are formed from a second reaction mixture, which comprises C2-40 diisocyanates and chain-extending monomers; and wherein the dihydroxyl-terminated polyesters are formed from a third reaction mixture, which comprises C9-22 diols and C7-22 dicarboxylic acids or esters thereof.
Further aspects and embodiments are disclosed in the Detailed Description.
The following drawings are provided for purposes of illustrating various embodiments of the compounds, compositions, and methods disclosed herein. The drawings are provided for illustrative purposes only, and are not intended to describe any preferred compounds, preferred compositions, or preferred methods, or to serve as a source of any limitations on the scope of the claimed inventions.
), and (c) percentage loss of sample weight and molecular weight (Mn) with immersion time for PU2.1 and ND-B. Curved lines in panels (a) and (b) are fits to the exponential decay function and in panel (c) are guides for the eye.
The following description recites various aspects and embodiments of the inventions disclosed herein. No particular embodiment is intended to define the scope of the invention. Rather, the embodiments provide non-limiting examples of various compositions, and methods that are included within the scope of the claimed inventions. The description is to be read from the perspective of one of ordinary skill in the art. Therefore, information that is well known to the ordinarily skilled artisan is not necessarily included.
The following terms and phrases have the meanings indicated below, unless otherwise provided herein. This disclosure may employ other terms and phrases not expressly defined herein. Such other terms and phrases shall have the meanings that they would possess within the context of this disclosure to those of ordinary skill in the art. In some instances, a term or phrase may be defined in the singular or plural. In such instances, it is understood that any term in the singular may include its plural counterpart and vice versa, unless expressly indicated to the contrary.
As used herein, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. For example, reference to “a substituent” encompasses a single substituent as well as two or more substituents, and the like.
As used herein, “for example,” “for instance,” “such as,” or “including” are meant to introduce examples that further clarify more general subject matter. Unless otherwise expressly indicated, such examples are provided only as an aid for understanding embodiments illustrated in the present disclosure, and are not meant to be limiting in any fashion. Nor do these phrases indicate any kind of preference for the disclosed embodiment.
As used herein, “reaction” and “reacting” refer to the conversion of a substance into a product, irrespective of reagents or mechanisms involved.
As used herein, “polymer” refers to a substance having a chemical structure that includes the multiple repetition of constitutional units formed from substances of comparatively low relative molecular mass relative to the molecular mass of the polymer. The term “polymer” includes soluble and/or fusible molecules having chains of repeat units, and also includes insoluble and infusible networks.
As used herein, “prepolymer” refers to a polymer that can undergo further reaction to contribute constitutional units to the chemical structure of a different polymer.
As used herein, “monomer” refers to a substance that can undergo a polymerization reaction to contribute constitutional units to the chemical structure of a polymer.
As used herein, “polyurethane” refers to a polymer comprising two or more urethane (or carbamate) linkages. Other types of linkages can be included, however. For example, in some instances, the polyurethane or polycarbamate can contain urea linkages, formed, for example, when two isocyanate groups can react. In some other instances, a urea or urethane group can further react to form further groups, including, but not limited to, an allophanate group, a biuret group, or a cyclic isocyanurate group. In some embodiments, at least 70%, or at least 80%, or at least 90%, or at least 95% of the linkages in the polyurethane or polycarbamate are urethane linkages. Such “polyurethanes” can include polyurethane block copolymers, which refers to a block copolymer, where one or more of the blocks are a polyurethane or a polycarbamate. Other blocks in the “polyurethane block copolymer” may contain few, if any, urethane linkages. For example, in some polyurethane block copolymers, at least one of the blocks is a polyether or a polyester and one or more other blocks are polyurethanes or polycarbamates.
As used herein, “polyester” refers to a polymer comprising two or more ester linkages. Other types of linkages can be included, however. In some embodiments, at least 80%, or at least 90%, or at least 95% of the linkages in the polyester are ester linkages. The term can refer to an entire polymer molecule, or can also refer to a particular polymer sequence, such as a block within a block copolymer. The term “dihydroxyl polyester” refers to a polyester having two or more free hydroxyl groups, e.g., at the terminal (e.g., reacting) ends of the polymer (i.e., a “dihydroxyl-terminated polyester”). In some embodiments, such polyesters have exactly two free hydroxyl groups.
As used herein, “alcohol” or “alcohols” refer to compounds having the general formula: R—OH, wherein R denotes any organic moiety (such as alkyl, aryl, or silyl groups), including those bearing heteroatom-containing substituent groups. In certain embodiments, R denotes alkyl, alkenyl, aryl, or alcohol groups. In certain embodiments, the term “alcohol” or “alcohols” may refer to a group of compounds with the general formula described above, wherein the compounds have different carbon lengths. The term “hydroxyl” refers to a —OH moiety. In some cases, an alcohol can have more than two or more hydroxyl groups. As used herein, “diol” and “polyol” refer to alcohols having two or more hydroxyl groups.
As used herein, “amine” or “amines” refer to compounds having the general formula: R—NH2, wherein R denotes any organic moiety (such as alkyl, aryl, or silyl groups), including those bearing heteroatom-containing substituent groups. In certain embodiments, R denotes alkyl, alkenyl, aryl, or alcohol groups. In certain embodiments, the term “amine” or “amines” may refer to a group of compounds with the general formula described above, wherein the compounds have different carbon lengths. The term “amino” refers to a —NH2 moiety. In some cases, an amine can have two or more amino groups. As used herein, “diamine” and “polyamine” refer to amines having two or more amino groups.
As used herein, “isocyanate” or “isocyanates” refer to compounds having the general formula: R—NCO, wherein R denotes any organic moiety (such as alkyl, aryl, or silyl groups), including those bearing heteroatom-containing substituent groups. In certain embodiments, R denotes alkyl, alkenyl, aryl, or alcohol groups. In certain embodiments, the term “isocyanate” or “isocyanates” may refer to a group of compounds with the general formula described above, wherein the compounds have different carbon lengths. The term “isocyanato” refers to a —NCO moiety. In some cases, an isocyanate can have more than two or more isocyanato groups. As used herein, “diisocyanate” and “polyisocyanate” refer to isocyanates having two or more isocyanato groups.
As used herein, “carboxylic acid” or “carboxylic acids” refer to compounds having the general formula: R—CO2H, wherein R denotes any organic moiety (such as alkyl, aryl, or silyl groups), including those bearing heteroatom-containing substituent groups. In certain embodiments, R denotes alkyl, alkenyl, aryl, or alcohol groups. In certain embodiments, the term “carboxylic acid” or “carboxylic acids” may refer to a group of compounds with the general formula described above, wherein the compounds have different carbon lengths. The term “carboxyl” refers to a —CO2H moiety. In some cases, an isocyanate can have more than two or more carboxy groups. As used herein, “dicarboxylic acid” and “polycarboxylic acid” refer to carboxylic acids having two or more carboxyl groups.
The terms “group” or “moiety” refers to a linked collection of atoms or a single atom within a molecular entity, where a molecular entity is any constitutionally or isotopically distinct atom, molecule, ion, ion pair, radical, radical ion, complex, conformer etc., identifiable as a separately distinguishable entity.
As used herein, “mix” or “mixed” or “mixture” refers broadly to any combining of two or more compositions. The two or more compositions need not have the same physical state; thus, solids can be “mixed” with liquids, e.g., to form a slurry, suspension, or solution. Further, these terms do not require any degree of homogeneity or uniformity of composition. This, such “mixtures” can be homogeneous or heterogeneous, or can be uniform or non-uniform. Further, the terms do not require the use of any particular equipment to carry out the mixing, such as an industrial mixer.
As used herein, the term “natural oil” or “lipid” refers to oils derived from various plants or animal sources. These terms include natural oil derivatives, unless otherwise indicated. The terms also include modified plant or animal sources (e.g., genetically modified plant or animal sources), unless indicated otherwise. Examples of natural oils include, but are not limited to, vegetable oils, algae oils, fish oils, animal fats, tall oils, derivatives of these oils, combinations of any of these oils, and the like. Representative non-limiting examples of vegetable oils include rapeseed oil (canola oil), coconut oil, corn oil, cottonseed oil, olive oil, palm oil, peanut oil, safflower oil, sesame oil, soybean oil, sunflower oil, linseed oil, palm kernel oil, tung oil, jatropha oil, mustard seed oil, pennycress oil, camelina oil, hempseed oil, and castor oil. Representative non-limiting examples of animal fats include lard, tallow, poultry fat, yellow grease, and fish oil. Tall oils are by-products of wood pulp manufacture. In some embodiments, the natural oil or natural oil feedstock comprises one or more unsaturated glycerides (e.g., unsaturated triglycerides).
As used herein, “natural oil derivatives” refers to the compounds or mixtures of compounds derived from a natural oil using any one or combination of methods known in the art. Such methods include but are not limited to saponification, fat splitting, transesterification, esterification, hydrogenation (partial, selective, or full), isomerization, oxidation, and reduction. Representative non-limiting examples of natural oil derivatives include gums, phospholipids, soapstock, acidulated soapstock, distillate or distillate sludge, fatty acids and fatty acid alkyl ester (e.g. non-limiting examples such as 2-ethylhexyl ester), hydroxy substituted variations thereof of the natural oil. For example, the natural oil derivative may be a fatty acid methyl ester (“FAME”) derived from the glyceride of the natural oil.
As used herein, “alkyl” refers to a straight or branched chain saturated hydrocarbon having 1 to 30 carbon atoms, which may be optionally substituted, as herein further described, with multiple degrees of substitution being allowed. Examples of “alkyl,” as used herein, include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, isobutyl, n-butyl, sec-butyl, tert-butyl, isopentyl, n-pentyl, neopentyl, n-hexyl, and 2-ethylhexyl.
For any compound, group, or moiety, the number carbon atoms in that compound, group, or moiety is represented by the phrase “Cx-y” which refers to an such a compound, group, or moiety, as defined, containing from x to y, inclusive, carbon atoms. Thus, “C1-6alkyl” refers to an alkyl chain having from 1 to 6 carbon atoms.
As used herein, “comprise” or “comprises” or “comprising” or “comprised of” refer to groups that are open, meaning that the group can include additional members in addition to those expressly recited. For example, the phrase, “comprises A” means that A must be present, but that other members can be present too. The terms “include,” “have,” and “composed of” and their grammatical variants have the same meaning. In contrast, “consist of” or “consists of” or “consisting of” refer to groups that are closed. For example, the phrase “consists of A” means that A and only A is present.
As used herein, “or” is to be given its broadest reasonable interpretation, and is not to be limited to an either/or construction. Thus, the phrase “comprising A or B” means that A can be present and not B, or that B is present and not A, or that A and B are both present. Further, if A, for example, defines a class that can have multiple members, e.g., A1 and A2, then one or more members of the class can be present concurrently.
As used herein, the various functional groups represented will be understood to have a point of attachment at the functional group having the hyphen or dash (-) or an asterisk (*). In other words, in the case of —CH2CH2CH3, it will be understood that the point of attachment is the CH2 group at the far left. If a group is recited without an asterisk or a dash, then the attachment point is indicated by the plain and ordinary meaning of the recited group.
In some instances herein, organic compounds are described using the “line structure” methodology, where chemical bonds are indicated by a line, where the carbon atoms are not expressly labeled, and where the hydrogen atoms covalently bound to carbon (or the C—H bonds) are not shown at all. For example, by that convention, the formula
represents n-propane.
As used herein, multi-atom bivalent species are to be read from left to right. For example, if the specification or claims recite A-D-E and D is defined as —OC(O)—, the resulting group with D replaced is: A-OC(O)-E and not A-C(O)O-E.
Unless a chemical structure expressly describes a carbon atom as having a particular stereochemical configuration, the structure is intended to cover compounds where such a stereocenter has an R or an S configuration.
Other terms are defined in other portions of this description, even though not included in this subsection.
In a first aspect, the disclosure provides polymer compositions, comprising one or more urethane polymers formed from a first reaction mixture, which comprises chain-extending monomers and diisocyanate-terminated poly(ester urethane) prepolymers; wherein the diisocyanate-terminated poly(ester urethane) prepolymers are formed from a second reaction mixture, which comprises C2-40 diisocyanates and dihydroxyl-terminated polyesters; and wherein the dihydroxyl-terminated polyesters are formed from a third reaction mixture, which comprises C9-22 diols and C7-22 dicarboxylic acids or esters thereof.
The denotation of the “first,” “second,” and “third” reaction mixture does not imply any ordering of steps, but merely distinguishes the two reaction mixtures from each other.
Any suitable chain-extending monomers can be used. In some embodiments, the chain-extending monomers comprise diols, diamines, or combinations thereof. In some embodiments, the chain-extending monomers comprise C9-22 diols, C9-20diols, or C9-18diols, or C9-16diols. In some embodiments, the chain-extending monomers are 1,9-nonanediol.
Any suitable C2-40 diisocyanates can be used in the above embodiments. In some such embodiments, the C2-40 diisocyanates are C2-30diisocyanates, or C3-20diisocyanates, or C4-15 diisocyanates, or C5-10diisocyanates. In some such embodiments, the C2-40 diisocyanates are 1,7-heptamethylene diisocyanate.
Any suitable C9-22 diols can be used to make the polyester in any of the above embodiments. In some such embodiments, the C9-22 diols are C9-20diols, or C9-18 diols, or C9-16 diols. In some embodiments, the C9-22 diols are 1,9-nonanediol. Further, any suitable C7-22 dicarboxylic acids or esters thereof (e.g., C1-6 alkyl esters, such as methyl esters) can be used to make the polyester in any of the above embodiments. In some such embodiments, the C7-22 dicarboxylic acids or esters thereof are C7-20dicarboxylic acids, or C7-18dicarboxylic acids, C7-16dicarboxylic acids, or esters of thereof. In some such embodiments, the C7-22 dicarboxylic acids or esters thereof are azelaic acid or esters thereof.
The dihydroxyl-terminated polyesters used in any of the above embodiments can have any suitable properties. In some such embodiments, the dihydroxyl-terminated polyesters have a number-average molecular weight (Mn) of at least 3000 g/mol, or at least 3500 g/mol, or at least 4000 g/mol, or at least 4500 g/mol. In some such embodiments, the dihydroxyl-terminated polyesters have a polydispersity index ranging from 1 to 2.
In some embodiments, it may be desirable to make the polyester from renewable materials. Thus, in some embodiments, the dihydroxyl-terminated polyesters are formed from lipid-derived monomers. In some such embodiments, the dihydroxyl-terminated polyesters have a renewable carbon content of at least 80%, or at least 85%, or at least 90%, or at least 95%, or at least 97%, or at least 98%, or at least 99%. In some such embodiments, the dihydroxyl-terminated polyesters have a renewable carbon content of 100%.
The polymer compositions of the foregoing embodiments can have any suitable physical properties. In some embodiments, the polymer composition exhibits one or more of the following properties: an initial modulus ranging from 46 MPa to 147 MPa; an ultimate tensile strength ranging from 7.7 MPa to 14.7 MPa; or an ultimate elongation at break ranging from 195% to 492%. In some embodiments, the polymer compositions comprise urethane polymers having a hard segment (the polycarbamate segment) and a soft segment (the polyester segment), wherein the hard segment exhibits one or more of the following properties: an onset of melting temperature of about 60° C.; an offset temperature of about 107° C.; or a peak melting temperature ranging from 84° C. to 88° C. In some further such embodiments, the soft segment exhibits one or more of the following properties: an onset of melting temperature ranging from −11.5° C. to −8.9° C.; an offset temperature of about 50° C.; a peak melting temperature of about 32° C.; or a glass transition temperature ranging from −35° C. to −23° C. In some such embodiments, the soft segment exhibits an enthalpy of melting ranging from 26.0 J/g to 30.7 J/g. In some such embodiments, the hard segment exhibits an enthalpy of melting ranging from 11.5 J/g to 19.8 J/g. In some embodiments, the polymer composition exhibits a degree of crystallinity ranging from 18% to 44%. In some such embodiments, the polymer composition exhibits one or more of the following properties: an onset temperature of thermal decomposition at 5% weight loss of about 259° C.; a peak decomposition temperature of about 292° C. for the hard segment; a peak decomposition temperature of about 392° C. for the soft segment; or a pyrolysis temperature of about 450° C. As used herein, the term “about” encompasses the range of error in making the measurement, which, in some embodiments is within ±3° C.
In some embodiments, it can be desirable that the dihydroxyl-terminated polyesters have certain properties. In some embodiments, the dihydroxyl-terminated polyesters exhibit one or more of the following properties: an onset temperature of thermal decomposition at 5% weight loss of about 214° C.; a peak decomposition temperature of about 412° C.; or a pyrolysis temperature of about 457° C.
In some embodiments of any of the aforementioned embodiments, the polymer composition can have certain desirable degradation characteristics. Thus, in some embodiments, upon immersing the one or more polymers in water at 80° C. for 30 days, the one or more polymers degrade into one or more hydrolyzed products, the one or more hydrolyzed products having a weight-average molecular weight (Mw) of no more than 4000 g/mol. In some embodiments, the polymer composition exhibits one or more of the following properties: an increased enthalpy of melting ranging from 26.3 J/g to 77.4 J/g following immersion of the polymer composition in water for 5 days at 80° C.; or a decreased enthalpy of about 28 J/g following immersion of the polymer composition in water for 20 days at 80° C. In some embodiments, the polymer composition undergoes tensile failure in no more than 10 days of immersion in water at 80° C. In some embodiments, the polymer composition reaches its tensile half-life in no more than one day upon immersion in water at 80° C.
In other aspects, the disclosure provides polymer compositions, comprising one or more urethane polymers formed from a first reaction mixture, which comprises diisocyanate-terminated poly(ester urethane) prepolymers and dihydroxyl-terminated polyesters; wherein the diisocyanate-terminated poly(ester urethane) prepolymers are formed from a second reaction mixture, which comprises C2-40 diisocyanates and chain-extending monomers; and wherein the dihydroxyl-terminated polyesters are formed from a third reaction mixture, which comprises C9-22 diols and C7-22 dicarboxylic acids or esters thereof.
The denotation of the “first,” “second,” and “third” reaction mixture does not imply any ordering of steps, but merely distinguishes the three different reaction mixtures from each other.
Any suitable chain-extending monomers can be used. In some embodiments, the chain-extending monomers comprise diols, diamines, or combinations thereof. In some embodiments, the chain-extending monomers comprise C9-22 diols, C9-20 diols, or C9-18 diols, or C9-16 diols. In some embodiments, the chain-extending monomers are 1,9-nonanediol.
Any suitable C2-40 diisocyanates can be used in the above embodiments. In some such embodiments, the C2-40 diisocyanates are C2-30diisocyanates, or C3-20diisocyanates, or C4-15diisocyanates, or C5-10diisocyanates. In some such embodiments, the C2-40 diisocyanates are 1,7-heptamethylene diisocyanate.
Any suitable C9-22 diols can be used to make the polyester in any of the above embodiments. In some such embodiments, the C9-22 diols are C9-20diols, or C9-18diols, or C9-16diols. In some embodiments, the C9-22 diols are 1,9-nonanediol. Further, any suitable C7-22 dicarboxylic acids or esters thereof (e.g., C1-6 alkyl esters, such as methyl esters) can be used to make the polyester in any of the above embodiments. In some such embodiments, the C7-22 dicarboxylic acids or esters thereof are C7-20 dicarboxylic acids, or C7-18 dicarboxylic acids, C7-16 dicarboxylic acids, or esters of thereof. In some such embodiments, the C7-22 dicarboxylic acids or esters thereof are azelaic acid or esters thereof.
The dihydroxyl-terminated polyesters used in any of the above embodiments can have any suitable properties. In some such embodiments, the dihydroxyl-terminated polyesters have a number-average molecular weight (Mn) of at least 3000 g/mol, or at least 3500 g/mol, or at least 4000 g/mol, or at least 4500 g/mol. In some such embodiments, the dihydroxyl-terminated polyesters have a polydispersity index ranging from 1 to 2.
In some embodiments, it may be desirable to make the polyester from renewable materials. Thus, in some embodiments, the dihydroxyl-terminated polyesters are formed from lipid-derived monomers. In some such embodiments, the dihydroxyl-terminated polyesters have a renewable carbon content of at least 80%, or at least 85%, or at least 90%, or at least 95%, or at least 97%, or at least 98%, or at least 99%. In some such embodiments, the dihydroxyl-terminated polyesters have a renewable carbon content of 100%.
The TPEUs disclosed herein can be synthesized by any suitable means, although some means may be more desirable than others. Suitable synthetic methodologies are disclosed in the Examples, below. The claims to the compounds, or to compositions including the compounds, are not limited in any way by the synthetic method used to make the compounds.
The following examples are provided to illustrate one or more preferred embodiments of the invention. Numerous variations can be made to the following examples that lie within the scope of the claimed inventions.
Stannous octoate (Sn(Oct)2) (98%), dibutylamine (98%), 1,9-nonanediol (98%), calcium hydride (98%), anhydrous tetrahydrofuran (THF), calcium hydride (98%), N-methyl-2-pyrrolidone (NMP), 1, 3 dimethyl-2-imidazolidinone (DMI), dimethyl sulfoxide (DMSO) and diethyl ether were purchased from Sigma Aldrich (Oakville, Ontario), Canada. Chloroform (CHCl3), methanol and dimethyl formamide (DMF) were obtained from ACP Chemical Int. (Montreal, Quebec), Canada. Clear glass laboratory bottles, 60 mL, with polyethylene cone-lined caps were purchased from Fisher Scientific (Whitby, Ontario). All reagents except DMF and THF were used as obtained. DMF was dried overnight over calcium hydride followed by vacuum distillation (˜300 Torr). THF was distilled after drying overnight over 4 A molecular sieves. PEDs of molecular weight 2000 g/mol were synthesized from oleic acid-derived azelaic acid and 1, 9 nonanediol as described in Shetranjiwalla et al., Polymer, vol 92, pp 140-152 (2016) 1,7-Heptamethylene diisocyanate (97%, 180 g/mol) was also synthesized from azelaic acid disclosed in in Hojabri et al., Biomacromolecules, vol. 10, pp. 884-891 (2009).
The segmented TPEU elastomers were synthesized by reacting molecular weight controlled PEDs and HPMDI with 1,9-nonanediol (ND) in the presence of Sn(Oct)2 using the two stage pre-polymer polymerization method; pre-polymer method A, where ND is added in step 2 of polymerization and pre-polymer method B where ND is added in step 1 of the polymerization, which is illustrated in
In Table 1, the nomenclature, recipe for the polymerization and the yield (%) of the TPEUs is shown. The ratios of HPMDI (1,7 heptamethylene diisocyanate), ND (1,9 nonanediol) as chain extender and PED (polyester diol) used in the synthesis are molar.
In the pre-polymer method A, excess HPMDI (0.63 g, 3.5 mmol) was dissolved in 6.3 mL of DMF in a round bottom flask attached to a thermometer and stirred under an inert atmosphere. The PED (1.65 g, 0.09 mmol) and catalyst Sn(Oct)2 (0.07 g, 0.17 mmol) were dissolved in 16.5 mL of DMF and then added to HPMDI through an addition funnel. The reaction was constantly stirred (600 rpm) at 85° C. for 5 h. In the second step, ND diol (1.7 mmol) and catalyst (0.0064 g) was dissolved in 1.7 mL of DMF and added to the HPMDI-PED-HPMDI pre-polymer (
The pre-polymer method B differed from method A only in the sequence of addition of reactants. In pre-polymer method B, excess HPMDI (0.63 g, 3.5 mmol) was dissolved in 6.3 mL of DMF and stirred at 85° C. In the first step, ND diol (1.7 mmol) and catalyst (0.0064 g), dissolved in 1.7 mL of DMF was added to HPMDI from a dropping funnel under constant stirring and reacted for 5 h. In the second step, PED (1.65 g, 0.09 mmol) and catalyst Sn(Oct)2 (0.07 g, 0.17 mmol) dissolved in 16.5 mL of DMF, was added to the -HPMDI-ND-HPMDI- pre-polymers (
Samples of entirely lipid-derived one-phase (PU2.1) and segmented (ND-B) elastomer films were immersed in 25 mL deionized water of pH 7.12 in sealed laboratory bottles that were placed in an oven at a temperature of 80±5° C. following a previously reported in Pretsch et al., Polymer Degradation and Stability, vol. 94(1), pp. 61-73 (2009) and Muller et al., Eu. Polymer Journal, vol. 46(8), pp. 1745-1758 (2010). Accelerated hydrolytic ageing was carried out for 30 days and ageing was tested on samples at 1 day (1 d), 5, 10, 15, 20, 25 and 30 d. Prior to DSC, TGA and tensile measurements the samples were taken out of the laboratory bottles and allowed to cool down to room temperature and dried with lint-free paper. FTIR samples were dried under vacuum at room temperature until constant weight prior to analysis.
For DSC studies, square samples between 5 and 6 mg were cut from the films. For TGA analysis rectangular samples weighing approximately 10 mg were used. For FTIR studies the samples were approximately 20 mg rectangles of thickness 0.64±0.1 mm. Dumb-bell shaped films of thickness 0.60±0.25 mm were used for tensile measurements.
Solubility tests were conducted on TPEU samples after they were purified and dried under vacuum until constant weight. Tests were performed for all samples in CHCl3, THF, DMF; NMP, DMI and DMSO, solvents with different polarities as indicated by their different dielectric constants, commonly used for processing polyurethanes. The sample (1 mg of TPEU in 1 mL of solvent) was stirred for thirty (30) minutes and left in the solvent for 2 days. The sample was then brought to the boiling point of the solvent at least three times for at least five (5) minutes each. In DMF, samples were refluxed for fifteen (15) minutes.
Scanning Electron Microscopy (SEM) was performed on a Phenom ProX apparatus (Phenom-World, The Netherlands) at an accelerating voltage of 15 kV and map intensity. Uncoated thin rectangular samples were fixed to the char reduction sample holder with conductive tape. Composite images were captured using the Automated Image Mapping software (Phenom-World, The Netherlands).
Fourier transform infrared spectroscopy (FTIR) was performed on a Thermo Scientific Nicolet 380 FTIR spectrometer (Thermo Electron Scientific Instruments, LLC, USA) equipped with a PIKE MIRacle attenuated total reflectance (ATR) system (PIKE Technologies, Madison, Wis., USA.). The sample was placed onto the ATR crystal area and held in place by the pressure arm. The spectrum was acquired in the 400-4000 cm−1 scanning range using 64 scans at a resolution of 4 wavenumbers. All spectra were recorded at ambient temperature.
The carbonyl hydrogen bonding index (R) which provides a measure of the increasing participation of the carbonyl groups in hydrogen bonding was determined as a ratio of the intensities of the normalized hydrogen-bonded (˜1714 cm−1 and ˜1690 cm−1) and the free (˜1731 cm−1) carbonyl stretching peaks. The 1780 cm−1 to 1660 cm−1 region was fitted with three Gaussians after baseline correction using OriginPro (version 9.2, 2015) software. The three Gaussians correspond to free carbonyl groups and hydrogen-bonded disordered and ordered carbonyl groups. The residual values for all Gaussian peak fits were better than 2 percent.
Proton Nuclear Magnetic Resonance (1H-NMR) spectra were recorded on a Bruker Advance III 400 spectrometer (BrukerBioSpin Mill GmbH, Karlsruhe, Germany) at a frequency of 400 MHz using a 5-mm BBO probe. The spectra were acquired at 25° C. over a 16-ppm window with a 1-s recycle delay, 32 transients. Spectra were Fourier transformed, phase corrected, and baseline corrected. Chemical shifts were referenced relative to the residual solvent peak (CDCl3, δ(1H)=7.26 ppm).
Degradation products were evaluated by 1H-NMR. The water in which the samples were hydrothermally aged was collected and dried completely. The residual products were dissolved in CDCl3.
Thermogravimetric analysis (TGA) was carried out on a Q500 TGA model (TA instrument, Newcastle, Del., USA), under dry nitrogen of 40 mL/min (balance purge flow) and 60 mL/min (sample purge flow). Approximately 9.0-10.0 mg of sample was loaded in an open TGA platinum pan that was equilibrated at 25° C. and heated to 600° C. at 10° C./min.
Films for tensile and dynamical mechanical analysis (DMA) testing were prepared on a Carver 12-ton hydraulic heated bench press (Model 3851-0- Wabash, Ind., USA). The dry samples were melt pressed at 150° C. and cooled at a controlled rate of 5° C./min. The mechanical properties of the TPEU films were measured at room temperature (RT=23° C.) by uniaxial tensile testing using a texture analyzer (Texture Technologies Corp, NJ, USA) equipped with a 2-kg load cell following the ASTM D882 procedure. The sample was stretched at a rate of 5 mm/min from a gauge of 35 mm at room temperature. The reported results are the average from at least four specimens.
DMA was performed on a Q800 model DMA (TA Instruments, New Castle, DA) equipped with a liquid nitrogen cooling system. The measurements were performed on rectangular samples (17.5 mm×10 mm×0.6 mm) under the flexural oscillation mode following ASTM E1640 standard. The frequency and amplitude were fixed at 1 Hz and 15 μm, respectively. The sample was equilibrated −90° C. for 5 min then heated at 2° C./min to 40° C. The data was analyzed with TA Instruments Universal Analysis 2000 software.
Wide-angle x-ray diffraction (WAXD) measurements were performed on a PANalytical EMPYREAN diffractometer (PANalytical B.V, Lelyweg, The Netherlands) equipped with a filtered CuKα (λ=1.540598 Å) radiation source and PIXcel3D detector used in line-scanning mode. The XRD patterns were recorded between 3 and 50° (2θ) in 0.026 steps. The procedure was automated and controlled by PANalytical Data Collector (V 3.0c) software. The data analysis was carried out using PANalytical's X'Pert High Score 3.0.4 software. The percentage degree of crystallinity (XC) was estimated according to equation 3.
Where AC is the area under the crystal diffraction peaks and AA is the area under the amorphous halo. The amorphous contribution was fitted with two lines centered at 4.0 Å and 4.7 Å as usually done for semi-crystalline polymers [21, 22].
The relative crystallinity of the hydrolyzed TPEU (XC) was calculated as the ratio of its melting enthalpy) to the melting enthalpy of the pristine TPEU (ΔHm0); equation 4:
Differential Scanning calorimetry (DSC) measurements were carried out on Q200 model (TA instrument, Newcastle, Del., USA) under a dry nitrogen gas atmosphere following the ASTM D3418 standard. The sample (5.0-6.0 mg±0.6 mg), contained in a hermetically sealed aluminum pan, was first heated (referred to as the 1st heating cycle), to 180° C. and held at that temperature for 5 min to erase thermal history, and then cooled to −80° C. at 5° C./min. The sample was subsequently heated to 180° C. (referred to as the 2nd heating cycle) at 10° C./min. During the second heating cycle measurements were performed in the modulation mode with modulation amplitude of 1° C./min and period of 60 s.
DSC measurements on one-phase and segmented TPEU elastomer samples after hydrothermal ageing were also carried out under an inert N2 atmosphere. Samples contained in a hermetically sealed aluminum pan, were first cooled to −60° C. at 5° C./min and then heated to 90° C. for the one-phase TPEUs and 110° C. for the segmented TPEUs at 10° C./min, modulation amplitude of 1° C./min and a modulation period of 60 s. The sample was held at that temperature for 5 min and then cooled to −80° C. at 5° C./min.
Gel Permeation Chromatography (GPC) tests were carried out on the hydrolytically aged TPEU elastomer samples on a Waters Alliance e2695 separation module (Milford, Mass., USA), equipped with a Waters 2414 refractive index detector and a high resolution Styragel HRSE column (5 μm). Chloroform was used as the eluent with a flow rate of 0.5 mL/min. Detector and column temperatures were 40° C. and 43° C., respectively. The concentration of the sample was 1 mg/mL and the injection volume was 30 μL. Polystyrene standards (molecular weight range between 1.2×103 Da and 133×103 Da) were used to calibrate the curve.
The weight loss of the hydrothermally treated samples was determined by drying the remaining aged sample under vacuum until constant weight (W1) and comparing it to the original weight (W0) of the sample as a percentage; equation 4
The segmented TPEUs tested in a range of solvents with increasing polarity, as indicated by their increasing dielectric constants were insoluble at room temperature. At solvent boiling point, ND-B was insoluble in all solvents, whereas ND-A showed partial solubility in DMF and DMSO. The partial solubility of ND-A in DMF and DMSO is attributed to possibly a lower molecular weight as compared to ND-B and the one-phase TPEU PU2.1 (Table 2). These results are of practical importance for TPEU applications requiring high solvent-resistance. Table 2 shows the solubility results and the polarities of the solvents used in the experiment as indicated by their dielectric constants.
The solubility data were explained by the variation in hydrogen bonding of the TPEUs as estimated from the analysis of the C═O region (1660-1780 cm−1) of their FTIR spectra.
As evident from
The rate of reaction is rather governed by proximity effects arising from the molecular size of the diisocyanate terminated pre-polymers known to impact accessibility of the isocyanate groups for subsequent reaction. The different molecular sizes of the pre-polymers of ND-A and ND-B, pre-designed in the first stage of polymerization, result in the different reactivity in the following second stage and the subsequent difference in molecular weight and yield. The better reactivity of ND-B and subsequent better polymer yield after precipitation compared to ND-A is attributable to a more favorable spatial distance between the two isocyanate groups in the HPMDI-ND-HPMDI pre-polymers of ND-B compared to the HPMDI-PED-HPMDI pre-polymer of ND-A (a minimum of 43 carbons versus 25 carbons). Moreover, during the polymerization of ND-A, the concentration of the more reactive HPMDI monomer available to react with ND was lower in stage two. Also, the concentration of available HPMDI was probably further reduced by the potential organotin catalyst-mediated fragmentation of the PED, upsetting the overall NCO:OH stoichiometric imbalance in this stage and affecting the subsequent reaction with ND. This may explain the lower yield after precipitation (Table 1) and the lower molecular weight of ND-A compared to ND-B for which the concentration of the monomer diisocyanate available to react with PED in the second step was higher. Furthermore, because the chain extender was sandwiched between diisocyanate segments, a larger sequence length of the urethane hard segment is formed in ND-B (repeating unit x,
The average size of the microstructures increased from ˜0.7±0.2 μm for PU2.1, to 1.2±0.2 μm for ND-A and 2.3±0.7 μm for ND-B indicating an increase in urethane hard segment content and hydrogen bond density. ND-B showed much larger microstructures (
Thermal Stability
a and b show the DTG and TGA profiles for the segmented and one-phase TPEUs respectively. The corresponding onset temperatures of decomposition, Td(on), determined at 5.0% weight loss, DTG peak temperatures (Td) and weight loss obtained for each decomposition stage (ΔW) were recorded.
The series of weight loss steps corresponding to the decomposition the C—NH (280-300° C.), C—O (390-400° C.) and the C—C bonds (450° C.) are distinctly indicated by their characteristic temperature ranges. It is evident from the DTG peaks of
The higher thermal stability of the one-phase PU2.1 compared to the segmented TPEUs ND-A and ND-B, is attributable to various factors such as potentially higher molecular weight, higher polyester soft segment content, or increased resistance to thermal scission of the crystalline polyethylene-like linear chain stacking.
Melt Transition and Crystallization Behavior
The distinct phase separation of the urethane hard segments and the polyester soft segments for segmented TPEUs was confirmed by the DSC thermograms in
Table 3 shows thermal data obtained during the second heating cycle (10° C./min) of the segmented TPEUs. Tm(° C.) and ΔH (J/g): melting and enthalpy of melting, respectively. Tg (° C.): glass transition temperature obtained at a10° C./min and b20° C./min. The uncertainties attached to the characteristic temperatures and enthalpies are better than 2.5° C. and 2.8 J/g, respectively.
The effect of phase separation was reflected in a decreased onset (Ton), peak (Tm) temperatures and enthalpy (ΔH) of melting of the soft segments suggesting that less stable and less organized soft segment crystallites were formed in ND-A and ND-B compared to PU2.1. This is indicative of increased polyester soft segment block length due to improved phase separation. The higher Ton, Tm and ΔH in PU2.1 is attributed to the stabilizing influence of the phase-mixed urethane segments in the polyester soft segment domain.
The improved degree of phase separation in the segmented TPEUs ND-A and ND-B was reflected in the decreased peak temperatures (Tm) and enthalpy (ΔH) of melting of the soft segments compared to the melting of the co-continuous phase of PU2.1. This is explained by the increased phase separation of the polyester segments from the hydrogen-bonded urethane segments, and the resulting weaker attractions (van der Waals forces) in the soft segments of the segmented TPEUs as compared to the one-phase PU2.1. The melting parameters are lower in ND-B than ND-A, indicating that a better separation of the soft segment phase from the hard segment phase occurs in ND-B. PU2.1 exhibits a higher Tm and ΔH, attributable to its phase-mixed nature of urethane segments in the larger polyester matrix (83% versus 75% in ND-A and ND-B).
The melting data of the hydrogen-bonded urethane segments can be related to the extent of the hard segment distribution in the segmented TPEU. The lower enthalpy of ND-A hard segment crystallites compared to ND-B indicates a lower crystallinity ascribed to a lower hard segment hydrogen bond density. ND-A presented a lower value of Tm than ND-B indicating smaller urethane hard segment domains. ND-A and PU2.1 which share a similar structure of their amorphous soft segments, corresponding to the one-shot and polymerization protocol A followed, also show similar glass transition temperatures (Tg). ND-B exhibited the highest Tg attributed to the maximum restriction imposed on the soft segment chain mobility by the larger hard segment domains.
The stress-strain curves for the segmented TPEUs ND-A and ND-B are shown in
The TPEUs ND-A and ND-B shown in
The higher tensile strength and modulus of PU2.1 compared to ND-A and ND-B is the result of its much higher polyester crystallinity. Also, for aliphatic TPEUs with low hard segment content, the amorphous segments orient and crystallize under strain, acting as a stress bearing phase which further increase the tensile strength. Correspondingly, a linear trend for Young's modulus versus degree of crystallinity has been observed in linear polyethylene. PU2.1 also exhibited high strain attributed to the strain hardening typical of elastomers which is also visible in ND-B.
The strength and extensibility values for the entirely lipid-derived segmented TPEUs of the present disclosure approach those of the closest analogue of ultra-high molecular weight partially lipid-derived TPEUs from HPMDI, ND and petroleum-based PEAD (PLD in Table 3) synthesized by Li et al., Polymer, 2014, 55(26), 6764-6775) and also commercially available polyester grade thermoplastic elastomers synthesized from aliphatic diisocyanates (PGTE 1 and 2 in Table 4). The mechanical properties of the segmented TPEUs of this study are superior to the entirely lipid-derived TPUs synthesized from HPMDI, ND and oleic acid derived polyester diol, 18-octadec-9-endiol (ELD in Table 3).
Table 4 shows mechanical properties of TPEUs derived from tensile analysis. The uncertainties attached to Young's modulus, ultimate tensile strength, and elongation at break are the standard deviations of at least four runs and are better than 31.5 MPa, 1.9 MPa and 51.6% respectively. Polyester grade thermoplastic (PGTE) synthesized from aliphatic diisocyanates. PGTE1: PEARLCOAT Activa D198K and PGTE2: PEARLTHANE D91F88 (Merquinza).
The glass transition (Tg) as determined at the peak maximum of the loss modulus curve and was −25.1±0.7° C. for PU2.1, a value that is close to that for ND-A (−23.2±0.2° C.) indicating very close amorphous phase structures attributable to the one-shot method and the pre-polymers of the Protocol A. The much lower Tg of ND-B (−28.7±1.2° C.) can be ascribed to its more pronounced phase separation and greater purity of its polyester soft segments associated with the polymerization protocol B. The Tg for ND-B is the lowest by DMA in contrast to the Tg seen by DSC as a result of the difference in the sample processing for the two techniques. An extensive demixing of the hard and soft segments is observed during melt-processing for film formation for DMA analysis which enhances phase separation between hard and soft segments.
Structural Changes Due to Hydrothermal Ageing
The entirely lipid-derived segmented TPEUs ND-A and ND-B synthesized in this study differed in their structure and morphology from the one-phase PU2.1 elastomer. Therefore, it was expected that the response of the segmented and one-phase elastomers to hydrothermal ageing would be a function of their structures. ND-B was selected for hydrothermal analysis and comparison with the one-phase PU2.1 because it exhibited higher phase separation and better mechanical properties than ND-A.
The solubility, molecular weight and dispersity () of PU2.1 and ND-B are provided in Table 5.
Table 5 shows the solubility and GPC data of PU2.1 and ND-B after accelerated hydrolytic degradation. ti: Immersion time (days), Mw: weight average molecular weight (gmol−1), Mn: number average molecular weight (gmol−1), : Dispersity. Uncertainty on Mw, Mn and D are better than 3000 gmol−1, 418 gma−1 and 0.34, respectively.
The molecular weight and of both TPEUs decreased rapidly with immersion time (
ND-B which is a two-phase TPEU, has a well separated amorphous soft segment domain and low crystallinity. Water is easily diffused in the amorphous region leading to hydrolysis and some early erosion of the polymer. The production of carboxylic acid from the degradation of polyester segments as a result of hydrolysis can be related to the decrease in pH of the immersion water (from 7.4 to 4.5) observed between 5 and 10 days of accelerated degradation (Table 6). However, with increasing immersion time, weight loss recedes as water encounters the well-developed, degradation-resistant hard segment domains. In contrast, PU2.1 showed a lower initial weight loss attributed to the relatively inhibited access of water in the polymer due its higher crystallinity and also the embedded nature of the urethane segments in the soft segment domains which mitigate early erosion of the degradation products. This may explain the retention of neutral pH of the immersion water at 10 days (Table 6). However, PU2.1 recorded increased weight loss and a sharp drop in pH at 20 days, indicating a rapid deterioration of the polyester-rich matrix due to the accelerated penetration of water with increasing immersion time (after 10 days,
On hydrolysis, the polyester segments of TPEUs mainly decompose into starting diols and dicarboxylic acids, which further decompose to carbon dioxide and water. The urethane bonds also co-hydrolyze under high humidity, producing carbamic acid, which further reduces to amines and carbon dioxide.
The 1H-NMR spectra and the possible chemical structures for the degradation products of PU2.1 and ND-B after 10 days and 30 days of hydrolysis are shown in
Interestingly, the intensity of all peaks reduced from ti=10 days to ti=30 days for both polymers indicating that the TPEU molecular size was significantly deteriorated at this time. Also, new peaks at chemical shifts 1.89-191 ppm and 2.46-2.53 ppm were detected attributed to the methylene protons attached to the nitrogen in the amine (CH2NH2, peak h) and the carbamate groups (CH2NHC(O)O, peak i), respectively. The appearance of these peaks indicates the presence of degradation products associated with the hydrolysis of urethane bonds in the immersion water, as also seen by the rise in pH at 30 days. Moreover, at 30 days, ND-B which has a higher urethane content than PU2.1 shows two additional low-intensity peaks at 2.95-2.97 ppm and 5.73 ppm associated with urethane degradation, attributed to the methylene protons attached to the nitrogen of the carbamic acid group (CH2NHC(O)OH, peak j) and the proton attached to the nitrogen of the carbamic acid group (HNC(O)OH) respectively.
Aged samples of PU2.1 and ND-B extracted at selected immersion times were dried and analyzed with FTIR. The deconvolution of the FTIR 1780-1660 cm−1 spectral region of PU2.1 and ND-B into its free (˜1732 cm−1), disordered (˜1715 cm−1) and ordered (˜1690 cm−1) hydrogen-bonded carbonyl peaks are provided in
The first stage in the hydrolysis of PU2.1 (0-10 days, stage I in
The second stage (10-20 days) manifested with a gradual drop in R and DPS (stage II in
The drop in R in phase I in ND-B (0-5 days, region I in
Scanning electron microscopy (SEM) was used to analyze the surface topography of the TPEUs before and after four weeks of hydrolytic degradation. SEM images of pristine PU2.1 and ND-B, and after 30 days of immersion in water at 80° C. are shown in
The pores and cracks which show prominently on the surfaces of the hydrolyzed samples after 30 days of hydrolytic ageing (
Effect of Hydrothermal Ageing on Thermal Behavior
The endotherm at ˜50° C. (P2 in
A gradual increase in water absorption with immersion time was evident for both TPEUs from the increasing enthalpy of P1 (
The percentage moisture content was estimated from the ratio of the enthalpy of the ice melting peak of the sample (P1 in
As shown in
The enthalpy and temperature of melting and degree of crystallinity XC in
After 5 days of hydrolysis, the enthalpy and melting temperature and degree of crystallinity of both PU2.1 and ND-B decreased dramatically to a point where the endothermic peaks were no longer detectable by DSC. This is attributable to the continuous erosion of the soft segments which leads to the rapid decrease in crystal size and regularity to an extent at which they are no longer detectable.
An increased initial crystallinity of the hydrolyzed PU2.1 and ND-B samples, due to chemicrystallization and the subsequent degradation of the soft segments resulted in the inability to detect a distinct glass transition temperature for both elastomers.
Effect of Hydrothermal Ageing on Tensile Properties
As shown in
Similar losses of mechanical properties have been reported for hydrolyzed ester-based polymers such polyethylene terephthalate and poly(glycolic acid). The decline in mechanical properties was explained by the fragmentation along the tie-chains of the polyester segments which support the crystalline soft segment lamellae to transmit tensile loads. The chain scission of long chain molecules leads to the decrease in entanglement reducing maximum strain.
PU2.1 which is a TPEU with a high polyester content is expected to experience substantial fragmentation of the tie-chains and to present a large loss in tensile strength and modulus at the early stages of hydrothermal ageing. ND-B displayed a similar pattern of early deterioration of elongation also attributed to the fragmentation of its polyester segment tie chains. However, it retained modulus and a certain degree of tensile strength because at this stage, its well separated urethane phase was less affected by degradation and provided effective load bearing junctions.
Between 1 and 5 days, an insignificant decline in tensile strength and modulus was observed in PU2.1 attributed to the consideration of chemicrystallization of fragmented chains as revealed by the gradual decrease in enthalpy observed by DSC for the peak associated with the melting of the polyester soft segment phase during this time (
Interestingly, the deterioration of mechanical properties of TPEUs prior to extensive molecular weight decay or mass loss and resulting in the formation of carboxylic acid degradation products is characteristic of resorbable polymers used as scaffolds for tissue regeneration, highlighting the potential for entirely lipid-derived aliphatic TPEUs as credible candidates in biomedical applications.
Effect of Hydrothermal Ageing on Thermal Decomposition and Mass Loss
The effect of hydrolytic ageing on thermal decomposition was determined by TGA. The DTG curves of PU2.1 and ND-B are shown in
A common pattern of decomposition was evident in both polymers. Firstly, there was a gradual increase in the evaporation of moisture below 100° C. (D1 in
Free N—H bonds in the hard segments act as oxygen bonding sites and the C═O groups provide acceptor sites for the protons of the penetrating water molecules effectively integrating water as a bridge between the N—H and C═O groups or between two carbonyl groups, resulting in stable hard segment structures with new inter-urethane hydrogen-bonds that delay decomposition. However, with further hydrolysis (i.e. after 15 days of immersion), the excess water disrupts the hard segment bonding, forming weaker polymer-water interactions. Self-aggregated water molecules are evaporated earlier and the un-degraded water-free C—NH bonds then regain their initial decomposition temperature. The delay in decomposition due to the formation of new inter-urethane hydrogen bonds is supported by the increase in R and DPS as quantified by FTIR in phase II of the hydrothermal ageing process (
Thirdly, the DTG peak of C—NH (D2 in
The DTG peak corresponding to the ester degradation was absent after 25 days in ND-B and after 30 days in PU2.1, suggesting that stable intermediates which reduce the number of degradation stages were formed. This indicates that the slower degrading residual urethane groups offer a stabilization effect that mitigates polyester degradation. A similar stabilization of the polyester segment decomposition by the crystalline urethane segments has been observed in TPEUs.
Elastomeric, entirely lipid-derived segmented thermoplastic poly(ester urethane)s (TPEU) were synthesized from oleic acid derived polyester diols, 1,7-heptamethylene diisocyanate and 1,9-nonandiol. Phase separation, molecular weight, hydrogen bond density and thus hard segment distribution and crystallinity of the TPEUs were controlled by varying the polymerization protocol. The study demonstrates that the polymerization procedure can be customized for both hydrogen bond density and phase separation. The TPEUs which were produced using this approach presented very high molecular weight and excellent phase separation and showed rubber-like elastomeric properties. Their mechanical properties are superior to those of any other fully lipid-derived TPEUs reported in literature so far and compare very favorably to commercial petroleum based counterparts.
The hydrothermal ageing was shown to affect the morphological structure of the TPEU in a complex manner. PU2.1 and ND-B both displayed bulk degradation irrespective of their phase structure, showing deterioration of mechanical properties prior to significant mass loss. Three phases were observed in the hydrolytic degradation of the both one-phase and segmented TPEU elastomers. In both cases, the degradation started with the scission of the soft segments; followed by a step in which although the erosion resulted in smaller fragments, they reorganized without diffusing out of the material in what is known as “chemicrystallization”, and in lastly the acceleration of the degradation of the ester phase leading to a brittle failure. Extensive hydrolysis resulted in the degradation of both the soft and hard segment domains after 30 days of ageing as evidenced by the analysis of the degradation products by 1H-NMR. The structure of the phase separated TPEU was revealed to offer a somehow higher protection against thermal ageing through its nanoscale crystalline load bearing phase than the continuous structure of the one-phase TPEU. The two-phase ND-B also showed a higher resistance to degradation than the one-phase PU2.1 based on the SEM images.
The continued deterioration of the mechanical properties of the TPEUs was related to the loss of molecular weight and PDI and directly correlated to the drop in crystallinity as revealed by DSC. Noticeably, the TPEU of the present work showed a very short tensile half-life, indicating that they are easily fragmentable and can significantly biodegrade after a successful service life.
The present application claims the benefit of priority from U.S. provisional application No. 62/259,771 filed on Nov. 25, 2015, the contents of which are incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62259771 | Nov 2015 | US |
