Patent Application
20150065682
This application relates to aliphatic polyesters derived from medium and long chain ω-hydroxy fatty acids (ω-OHFA) and their respective methyl esters (Me-ω-OHFA), which arise from the functionalization of natural oils. Such ω-hydroxy fatty acids and their respective methyl esters undergo melt polycondensation to produce aliphatic polyesters.
Growing concerns over the environmental impacts of non-biodegradable plastic waste and the need for sustainability have stimulated research efforts on biodegradable polymers from renewable resources. Rising costs and dwindling petrochemical feedstocks also make renewable resource-based materials attractive alternatives to their petroleum-based counterparts. Many of these efforts have concerned ester containing polymers such as polyesters, polyester amides, and polyester urethanes, where the polar ester groups (—COO—) offer biodegradability through hydrolytic and/or enzymatic degradation, and hydrophobicity through the long aliphatic segments.
Linear aliphatic polyesters of the [—(CH2)n—COO—]x homologue series, synthesized from lactones or hydroxyl acid/ester monomers derived from renewable carbon sources, have gained considerable attention because of their potential suitability in biomedical applications. The medium chain homologue poly(nonane lactone) derived from natural oils has been shown to exhibit improved thermal properties compared to poly(ε-caprolactone) (PCL) and has been suggested as potential replacement for petroleum derived PCL in drug delivery applications. Most of the earlier reported polyesters in this series, however, are short chain homologues, such as poly (glycolic acid), poly(3-hydroxy propionic acid), poly(4-hydroxy butyrate) etc., which suffer from poor thermal stability, low melting points, and consequently, poor melt processibility.
Long chain polyester homologues have recently attracted significant interest as potential new degradable analogues of linear polyethylene (PE, (—CH2—)n). Linear PE is one of the best-known commodity polymers, but due to its hydrophobicity and molecular size, is non-biodegradable. PE is used in large volumes for household products and packaging applications because of its adequate mechanical properties and its relatively lower cost compared to engineering polymers. Recent efforts have indicated that the PE-like properties of the long chain polyester homologues, along with biodegradability, present ecological advantages by offering alternative solutions to the PE commodity waste problem.
In some instances, ω-hydroxyl fatty ester monomers derived from triglycerides of natural oils are an inexpensive renewable feedstock which can be used as efficient routes to prepare the long chain homologues of the [—(CH2)n—COO—]x series. The natural oil triglycerides can be transformed chemically into different long chain w-hydroxy fatty acids by functionalization reactions such as, oxidation, reduction, epoxidation, hydroformylation, metathesis, etc., at the fatty acid double bonds. The various structure—property correlations for P(ω-OHFA)s are discussed in light of the PE-like behavior for [—(CH2)n—COO—]x aliphatic polyesters homologous series.
Long chain polyester homologues exhibit the orthorhombic crystalline structure reminiscent of linear PE. Recent studies comparing the crystallographic data of linear PE with poly(11-undecalactone) (PUDL, n=10), poly(12-dodecalactone) (PDDL, n=11), poly(15-pentadecalactone) (PPDL, n=14) and poly(16-hexadecalactone) (PHDL, n=15)—all obtained by ring opening polymerization from their corresponding non-renewable lactone monomers—found that the unit cell parameter along the fiber axis (c) increases with n. This was attributed to the molecular chains trying to achieve an all-trans planar zig-zag conformation, similarly to linear PE. Studies on PPDL derived from petroleum and poly(ω-hydroxyl tetradecanoic acid) derived from vegetable oil indicated that the effects of crystallinity and molecular weight on Young's modulus were similar to what was observed for linear PE. The variation of elongation at break with molecular weight was, however, different for the long chain homologues.
There are relatively few studies relating the physical properties to structure and molecular parameters for the long chain polyester homologues of [—(CH2)n—COO—]x despite their promising prospective applications, particularly in the biomedical sector. This type of knowledge is important to provide a realistic set of optimum attainable performance and trade-offs for these materials. Their use as PE analogues and for other targeted applications such as tissue engineering and drug delivery systems is tributary of a comprehensive understanding of the structure-function relationships as well as interrelationships between various properties.
The present effort details the synthesis of a group of certain medium and long chain ω-hydroxy esters having the general formula [HO—(CH2)n—COOCH3], namely methyl-9-hydroxynonanoate, [Me-ω-OHC9, (n=8)], methyl-13-hydroxytridecanoate, [Me-ω-OHC13, (n=12)], and methyl-18-hydroxyoctadecanoate, [Me-ω-OHC18 (n=17)], and certain ω-hydroxy fatty acids having the general formula [HO—(CH2)n—COOH], namely 9-hydroxynonanoic acid [(ω-OHC9), (n=8)], 13-hydroxytridecanoic acid, [(ω-OHC13), (n=12)], and 18-hydroxyoctadecanoic acid, [(ω-OHC18) (n=17)]. Such ω-hydroxy esters and ω-hydroxy fatty acids are derived from natural oils, and their corresponding polymers were obtained by melt polycondensation. Additionally, the present effort investigates the effects of structural and molecular parameters on the thermal and mechanical properties of ω-hydroxy ester based polymers. Additionally, the present effort investigates the co-polymerization of ω-hydroxy ester based polymers.
In one aspect of the invention, a monomer composition comprising ω-hydroxy esters having the formula of HO—(CH2)n—COOCH3 is disclosed, wherein n is between 12 and 17. Such ω-hydroxy esters are selected from the group consisting of methyl-13-hydroxytridecanoate, and methyl-18-hydroxyoctadecanoate.
In another aspect of the invention, a monomer composition comprising w-hydroxy fatty acids having the formula of HO—(CH2)n—COOH is disclosed, wherein n is between 12 and 17. Such ω-hydroxy fatty acids are selected from the group consisting of 13-hydroxytridecanoic acid, and 18-hydroxyoctadecanoic acid.
In another aspect of the invention, a polymer composition derived from monomer units comprising ω-hydroxy esters having the formula of HO—(CH2)n—COOCH3 is disclosed, wherein n is between 8 and 17. Such ω-hydroxy esters are selected from the group consisting of methyl-9-hydroxynonanoate methyl-13-hydroxytridecanoate, and methyl-18-hydroxyoctadecanoate.
In another aspect of the invention, a polymer composition derived from monomer units comprising ω-hydroxy fatty acids having the formula of HO—(CH2)n—COOH is disclosed. Such ω-hydroxy fatty acids are selected from the group consisting of 13-hydroxytridecanoic acid, and 18-hydroxyoctadecanoic acid.
In another aspect of the invention, a copolymer composition derived from monomer units comprising ω-hydroxy esters having the formula of HO—(CH2)n—COOCH3, wherein n is between 8 and 12, is disclosed. Such ω-hydroxy esters are selected from the group consisting of methyl 9-hydroxynonanoate and methyl-13-hydroxytridecanoate.
The synthesis of certain ω-hydroxy esters and ω-hydroxy fatty acids, including those having carbon chain lengths of 3 to 36 carbons, and preferably 9 to 22 carbons, occurs via the functionalization of natural oils. As used herein, the term “natural oil” may refer to oil derived from plants or animal sources. The term “natural oil” includes natural oil derivatives, unless otherwise indicated. Examples of natural oils include, but are not limited to, vegetable oils, algae 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 canola oil, rapeseed oil, coconut oil, corn oil, cottonseed oil, jojoba 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 oil, camelina oil, pennycress oil, hemp oil, algal 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 certain embodiments, the natural oil may be refined, bleached, and/or deodorized. In some embodiments, the natural oil may be partially or fully hydrogenated. In some embodiments, the natural oil is present individually or as mixtures thereof.
Natural oils generally comprise triglycerides of saturated and unsaturated fatty acids. Suitable fatty acids may be saturated or unsaturated (monounsaturated or polyunsaturated) fatty acids, and may have carbon chain lengths of 3 to 36 carbon atoms. Such saturated or unsaturated fatty acids may be aliphatic, aromatic, saturated, unsaturated, straight chain or branched, substituted or unsubstituted, fatty acids, and mono-, di-, tri-, and/or poly-acid variants, hydroxy-substituted variants, aliphatic, cyclic, alicyclic, aromatic, branched, aliphatic- and alicyclic-substituted aromatic, aromatic-substituted aliphatic and alicyclic groups, and heteroatom substituted variants thereof. Any unsaturation may be present at any suitable isomer position along the carbon chain to a person skilled in the art.
Some non-limiting examples of saturated fatty acids include propionic, butyric, valeric, caproic, enanthic, caprylic, pelargonic, capric, undecylic, lauric, tridecylic, myristic, pentadecanoic, palmitic, margaric, stearic, nonadecyclic, arachidic, heneicosylic, behenic, tricosylic, lignoceric, pentacoyslic, cerotic, heptacosylic, carboceric, montanic, nonacosylic, melissic, lacceroic, psyllic, geddic, ceroplastic acids.
Some non-limiting examples of unsaturated fatty acids include butenoic, pentenoic, hexenoic, pentenoic, octenoic, nonenoic acid, decenoic acid, undecenoic acid, dodecenoic acid, tridecenoic, tetradecenoic, pentadecenoic, palmitoleic, palmitelaidic oleic, ricinoleic, vaccenic, linoleic, linolenic, elaidic, eicosapentaenoic, behenic and erucic acids. Some unsaturated fatty acids may be monounsaturated, diunsaturated, tri unsaturated, tetraunsaturated or otherwise polyunsaturated, including any omega unsaturated fatty acids.
In most natural oils, there are a few different reactive sites which offer various functionalities. Typically, these reactive sites are: (i) one or more of the double bonds of an unsaturated fatty acid; (ii) the carboxyl ester group linking the fatty acid to the glycerol; (iii) allylic positions, and (iv) and the α-position of ester groups. Schematically, the reactive sites are shown below:
Reactive positions in triglycerides: ester groups (a), C═C double bonds (b), allylic positions (c), and the α-positions of ester groups (d).
The natural oils can be transformed chemically into different long chain w-hydroxy fatty acids and ω-hydroxy esters by functionalization reactions, including ozonolysis, hydrogenation, reduction, saponification, and/or metathesis, individually or in combinations thereof.
The term “ozonolysis” as used herein, means a method in which a C═C double bond of a hydrocarbon, more preferably an unsaturated fatty acid or a derivative thereof, such as an unsaturated ester derivative, is oxidatively cleaved as a result of the action of ozone on the molecule to form carbonyl products. In some embodiments, the unsaturated fatty acid to undergo ozonolysis may be butenoic, pentenoic, hexenoic, pentenoic, octenoic, nonenoic acid, decenoic acid, undecenoic acid, dodecenoic acid, tridecenoic, tetradecenoic, pentadecenoic, palmitoleic, palmitelaidic oleic, ricinoleic, vaccenic, linoleic, linolenic, elaidic, eicosapentaenoic, behenic and erucic acids. In some embodiments, the unsaturated ester derivative to undergo ozonolysis may be unsaturated fatty acid methyl esters such as methyl myristoleate, methyl 10-pentadecenoate, methyl palmitoleate, methyl 10-heptadecenoate, methyl elaidate, methyl linoleate, methyl linolenate, methyl oleate, methyl 11-eicosanoate, methyl 11,14-eicosadienoate, methyl 11,14,17-eicosatrienoate, methyl 13,16-docosadienoate, methyl erucate, and methyl nervonate.
The methods, agents and instruments suitable for carrying out the ozonolysis are conventionally known to a personal skilled in the art. Conventionally, ozonolysis is carried out in alcohols as solvents, the reaction mixture further comprising at least 0.5 percent by weight of water, based on the total amount of solvent. Usually, the unsaturated fatty acid or its derivative is present in a concentration of 0.1 to 1 mol/L. The ozonolysis is carried out preferably at temperatures from 0 to 40° C., more preferably at temperatures from 10 to 35° C., and particularly preferably at temperatures from 20 to 30° C. Usually, to produce the ozone, an ozone generator is used which uses technical-grade air or a mixture of carbon dioxide and oxygen as feed gas. The ozone is produced from the oxygen by means of non-luminous electric discharge. In the process, oxygen radicals are formed which form ozone molecules with further oxygen molecules. Using mechanistic terms, ozonolysis involves a [3+2]-cycloaddition of the ozone onto the double bond, which gives a primary ozonide, an unstable intermediate, which decomposes to give an aldehyde and a carbonyl oxide. The latter can either polymerize and/or dimerize to give a 1,2,4,5-tetraoxolane or, in a further cycloaddition, form a secondary ozonide. The secondary ozonide can then be worked-up oxidatively to give a carboxylic acid or reductively to give an aldehyde. The aldehyde can be reduced further as far as the alcohol. In some instances, reduction of ozonolysis products has been carried out with sodium borohydride, zinc/acetic acid solution, triphenylphosphine, dimethyl sulfide, or catalytic hydrogenation in the presence of a Raney nickel catalyst.
Hydrogenation may be conducted according to any known method for hydrogenating double bond-containing compounds. Hydrogenation may be carried out in a batch or in a continuous process and may be partial hydrogenation or complete hydrogenation. In a representative batch process, a vacuum is pulled on the headspace of a stirred reaction vessel and the reaction vessel is charged with the material to be hydrogenated. The material is then heated to a desired temperature. Typically, the temperature ranges from about 40° C. to 350° C., for example, about 50° C. to 300° C. or about 70° C. to 250° C. The desired temperature may vary, for example, with hydrogen gas pressure. Typically, a higher gas pressure will require a lower temperature. In a separate container, the hydrogenation catalyst is weighed into a mixing vessel and is slurried in a small amount of the material to be hydrogenated. When the material to be hydrogenated reaches the desired temperature, the slurry of hydrogenation catalyst is added to the reaction vessel.
Hydrogen gas is then pumped into the reaction vessel to achieve a desired pressure of H2 gas. Typically, the H2 gas pressure ranges from about 15 to 3000 psig, for example, about 15 psig to 120 psig. As the gas pressure increases, more specialized high-pressure processing equipment may be required. Under these conditions the hydrogenation reaction begins and the temperature is allowed to increase to the desired hydrogenation temperature (e.g., about 70° C. to 200° C.) where it is maintained by cooling the reaction mass, for example, with cooling coils. When the desired degree of hydrogenation is reached, the reaction mass is cooled to the desired filtration temperature.
In some embodiments, the ozonide product is hydrogenated in the presence of a metal catalyst, typically a transition metal catalyst, for example, nickel, copper, palladium, platinum, molybdenum, iron, ruthenium, osmium, rhodium, or iridium catalyst. Combinations of metals may also be used. Useful catalyst may be heterogeneous or homogeneous. The amount of hydrogenation catalysts is typically selected in view of a number of factors including, for example, the type of hydrogenation catalyst used, the amount of used, the degree of unsaturation in the material to be hydrogenated, the desired rate of hydrogenation, the desired degree of hydrogenation (e.g., as measure by iodine value (IV)), the purity of the reagent, and the H2 gas pressure.
In some embodiments, the hydrogenation catalyst comprises nickel that has been chemically reduced with hydrogen to an active state (i.e., reduced nickel) provided on a support. In some embodiments, the support comprises porous silica (e.g., kieselguhr, infusorial, diatomaceous, or siliceous earth) or alumina. The catalysts are characterized by a high nickel surface area per gram of nickel. In some embodiments, the particles of supported nickel catalyst are dispersed in a protective medium. In some embodiments, the catalyst is a Raney nickel catalyst.
Saponification generally refers to the hydrolysis of an ester of a natural oil, under basic conditions to form an alcohol and the salt of a carboxylic acid (carboxylates), and the additional provision of an excess of a strong acid, such as dilute hydrochloric acid or dilute sulfuric acid, to the solution if the carboxylic acid of the carboxylic acid salt is desired to be obtained. In some embodiments, the ester may be ω-hydroxy esters such as methyl-9-hydroxynonanoate, methyl-13-hydroxytridecanoate, and methyl-18-hydroxyoctadecanoate, and the carboxylic acid may be ω-hydroxy fatty acids, such as 9-hydroxynonanoic acid, 13-hydroxytridecanoic acid, and 18-hydroxyoctadecanoic acid. In some embodiments, saponification of a natural oil includes a hydrolysis reaction of the esters in the natural oil with a metal alkoxide, metal oxide, metal hydroxide or metal carbonate, preferably a metal hydroxide to form salts of the fatty acids (soaps) and free glycerol. Non-limiting examples of metals include alkaline earth metals, alkali metals, transition metals, and lanthanoid metals, individually or in combinations thereof. Any number of known metal hydroxide compositions may be used in this saponification reaction. In certain embodiments, the hydroxide is an alkali metal hydroxide. In one embodiment, the metal hydroxide is sodium hydroxide.
In some embodiments, a metathesis step, particularly a cross-metathesis step, may be used to generate certain ω-hydroxy esters, via cross-metathesis of an unsaturated fatty acid methyl ester and an unsaturated fatty alcohol. Such unsaturated fatty acid methyl esters may have between 6 and 24 carbon atoms, and include methyl myristoleate, methyl 10-pentadecenoate, methyl palmitoleate, methyl 10-heptadecenoate, methyl elaidate, methyl linoleate, methyl linolenate, methyl oleate, methyl 11-eicosanoate, methyl 11,14-eicosadienoate, methyl 11,14,17-eicosatrienoate, methyl 13,16-docosadienoate, methyl erucate, and methyl nervonate. Such unsaturated fatty alcohols may have between 8 and 24 carbon atoms, and may include oleyl, vaccenyl, linoleyl, linolenyl, palmitoleyl, and erucyl alcohols, as well as mixtures of any of the foregoing unsaturated fatty alcohols. In some embodiments, the fatty alcohol is oleyl alcohol or erucyl alcohol, and the unsaturated fatty acid methyl ester is methyl oleate or methyl erucate.
Metathesis is a catalytic reaction that involves the interchange of alkylidene units among compounds containing one or more double bonds (i.e., olefinic compounds) via the formation and cleavage of the carbon-carbon double bonds. The metathesis catalyst in this reaction may include any catalyst or catalyst system that catalyzes a metathesis reaction. Generally, cross metathesis may be represented schematically as shown in Equation A:
R1—CH═CH—R2+R3—CH═CH—R4⇄ R1—CH═CH—R3+R1—CH═CH—R4+R2—CH═CH—R3+R2—CH═CH—R4+R1—CH═CH—R1+R2—CH═CH—R2+R3—CH═CH—R3+R4—CH═CH—R4 (A)
Suitable homogeneous metathesis catalysts include combinations of a transition metal halide or oxo-halide (e.g., WOCl4 or WCl6) with an alkylating cocatalyst (e.g., Me4Sn). Preferred homogeneous catalysts are well-defined alkylidene (or carbene) complexes of transition metals, particularly Ru, Mo, or W. These include first and second-generation Grubbs catalysts, Grubbs-Hoveyda catalysts, and the like. Suitable alkylidene catalysts have the general structure:
M[X1X2L1L2(L3)n]=Cm═C(R1)R2
where M is a Group 8 transition metal, L1, L2, and L3 are neutral electron donor ligands, n is 0 (such that L3 may not be present) or 1, m is 0, 1, or 2, X1 and X2 are anionic ligands, and R1 and R2 are independently selected from H, hydrocarbyl, substituted hydrocarbyl, heteroatom-containing hydrocarbyl, substituted heteroatom-containing hydrocarbyl, and functional groups. Any two or more of X1, X2, L1, L2, L3, R1 and R2 can form a cyclic group and any one of those groups can be attached to a support.
First-generation Grubbs catalysts fall into this category where m=n=0 and particular selections are made for n, X1, X2, L1, L2, L3, R1 and R2 as described in U.S. Pat. Appl. Publ. No. 2010/0145086 (“the '086 publication”), the teachings of which related to all metathesis catalysts are incorporated herein by reference. Second-generation Grubbs catalysts also have the general formula described above, but L1 is a carbene ligand where the carbene carbon is flanked by N, O, S, or P atoms, preferably by two N atoms. Usually, the carbene ligand is part of a cyclic group. Examples of suitable second-generation Grubbs catalysts also appear in the '086 publication.
In another class of suitable alkylidene catalysts, L1 is a strongly coordinating neutral electron donor as in first- and second-generation Grubbs catalysts, and L2 and L3 are weakly coordinating neutral electron donor ligands in the form of optionally substituted heterocyclic groups. Thus, L2 and L3 are pyridine, pyrimidine, pyrrole, quinoline, thiophene, or the like. In yet another class of suitable alkylidene catalysts, a pair of substituents is used to form a bi- or tridentate ligand, such as a biphosphine, dialkoxide, or alkyldiketonate. Grubbs-Hoveyda catalysts are a subset of this type of catalyst in which L2 and R2 are linked. Typically, a neutral oxygen or nitrogen coordinates to the metal while also being bonded to a carbon that is α-, δ-, or γ- with respect to the carbene carbon to provide the bidentate ligand. Examples of suitable Grubbs-Hoveyda catalysts appear in the '086 publication.
The structures below provide just a few illustrations of suitable catalysts that may be used:
Heterogeneous catalysts suitable for use in the self- or cross-metathesis reaction include certain rhenium and molybdenum compounds as described, e.g., by J.C. Mol in Green Chem. 4 (2002) 5 at pp. 11-12. Particular examples are catalyst systems that include Re2O7 on alumina promoted by an alkylating cocatalyst such as a tetraalkyl tin lead, germanium, or silicon compound. Others include MoCl3 or MoCl5 on silica activated by tetraalkyltins. For additional examples of suitable catalysts for self- or cross-metathesis, see U.S. Pat. No. 4,545,941, the teachings of which are incorporated herein by reference, and references cited therein. See also J. Org. Chem. 46 (1981) 1821; J. Catal. 30 (1973) 118; Appl. Catal. 70 (1991) 295; Organometallics 13 (1994) 635; Olefin Metathesis and Metathesis Polymerization by Ivin and Mol (1997), and Chem. & Eng. News 80(51), Dec. 23, 2002, p. 29, which also disclose useful metathesis catalysts. Illustrative examples of suitable catalysts include ruthenium and osmium carbene catalysts as disclosed in U.S. Pat. Nos. 5,312,940, 5,342,909, 5,710,298, 5,728,785, 5,728,917, 5,750,815, 5,831,108, 5,922,863, 6,306,988, 6,414,097, 6,696,597, 6,794,534, 7,102,047, 7,378,528, and U.S. Pat. Appl. Publ. No. 2009/0264672 A1, and PCT/US2008/009635, pp. 18-47, all of which are incorporated herein by reference. A number of metathesis catalysts that may be advantageously employed in metathesis reactions are manufactured and sold by Materia, Inc. (Pasadena, Calif.).
Erucic acid (90% purity), methyl oleate (70% purity), oleyl alcohol (85% purity), Raney nickel 2800 (slurry in water), sodium sulfate (anhydrous) (Na2SO4), Ti(IV) isopropoxide (Ti(OiPr)4) (99.99% purity), 1-butanol (99.98% purity) sodium hydroxide, Grubbs 2nd generation catalyst and filter agent Celite®545 were purchased from Sigma-Aldrich. The reagents were used without further purification. Ozone was generated from an Azcozon Model RMU-DG3 ozone generator (AZCO Industries Limited, Canada) connected to a PSA Model Topaz oxygen generator (AirSep® Corporation). Molecular sieve type 3A was purchased from Fisher. Silica gel (230-400 mesh) and TLC plates (60 Å) were obtained from SiliCycle Inc., QC, Canada.
The chemical structures of (ω-OHFA)s and (Me-ω-OHFA)s prepared are listed in Table 1.
The preparation of (Me-ω-OHC9) and (Me-ω-OHC13) monomers from methyl fatty acids included two steps, namely, ozonolysis and hydrogenation. Methyl erucate, the reactant for Me-ω-OHC13 was prepared initially from erucic acid as discussed below.
Erucic acid (50 g, 0.14 mol.) was dissolved in 350 mL dry methanol in a three neck 1 L round bottomed flask. 10 mL of hydrochloric acid (37%) was added to catalyze the reaction. In order to absorb the water produced from the reaction; molecular sieve type 3A (10 g) was also added to the flask. The entire reaction was kept under reflux at 65° C. and stirred for 4 h. Thin layer chromatography (TLC) was used to monitor the progress of the reaction until the starting material was depleted. The reaction was then cooled down to room temperature, and quenched by adding 350 mL distilled water. The resulting mixture was extracted by 2×200 mL of ethyl acetate. Afterward, the ethyl acetate phase was washed by brine and dried over Na2SO4. The crude products were collected by removing the solvent under pressure. The desired product was purified by column chromatography hexane/ethyl acetate eluting solvent (30:1).
Methyl fatty acid (0.1 mol.) was dissolved in 200 mL of anhydrous ethyl alcohol in a three neck flask equipped with a magnetic stirrer, inlet for ozone and outlet for gas. The reaction setup was placed in an ice-salt bath and the temperature was maintained at −5° C. Ozone (62.0 g/m3) was then bubbled into the reaction mixture with a flow rate of 5 L/min. The reaction conditions were maintained at controlled temperature of <5° C. The reaction was monitored by TLC until the starting material was completely reacted, which takes about 35 to 40 min. The ozone generator was then shut off and the flask was purged with nitrogen for 10 min to remove any ozone residues in the reactor vessel.
The ozonide product was diluted with 200 mL of anhydrous ethyl alcohol and transferred into a hydrogenation vessel (600 mL, Parr Instrument Co.) equipped with a mechanical stirrer. Raney nickel (5.0 g, slurry in water) was added into the hydrogenation vessel. The reaction vessel was purged with nitrogen gas, and then charged with hydrogen to 100 psi. The temperature was raised to 70° C. After 4 h, heat was shut off and the reaction vessel was allowed to cool down to room temperature. The reaction vessel was finally purged with nitrogen gas to remove any residues of hydrogen. The resulting mixture was filtered through filter agent Celite®545 in a Buchner funnel. The filtrate was then transferred to a flask, and solvent was removed by rotary evaporation. The pure (Me-ω-OHC9) and (Me-ω-OHC13) products were obtained by column chromatography using ethyl acetate/hexane eluting mixture at 1:6 and 1:8 ratios, respectively.
In order to synthesize (ω-OHC9) and (ω-OHC13), the obtained (Me-ω-OHC9) and (Me-ω-OHC13) were saponified using 100 mL of sodium hydroxide solution (8%). The reaction was performed under reflux at 80° C. for 3 h. The resulting mixture was then cooled down to room temperature and washed by ether (3×100 mL). The aqueous layer was cooled down to 0° C., and then acidified by 8 mL concentrated HCl (36.5%). The acidified mixture was then extracted with ether (4×250 mL). The ether layers were combined and washed by brine (3×100 mL). The solution was then dried over magnesium sulfate and concentrated by rotary evaporation.
Me-ω-OHC13 was also synthesized by the same ozonolysis-reduction route discussed in
Me-ω-OHC18 was prepared by the cross metathesis of oleyl alcohol and methyl oleate followed by hydrogenation. ω-OHC18 was prepared from (Me-ω-OHC18) by saponification using 100 mL of sodium hydroxide solution (8%) as described in the same procedures as described above.
Methyl oleate (30.0 g, 0.1 mol.) and oleyl alcohol (30.0 g, 0.1 mol.) were transferred into a 500 mL three-necked round-bottomed flask equipped with a magnetic stirrer. The reaction mixture was stirred at 45° C. under nitrogen gas for 30 min. Grubbs catalyst, second generation (100 mg), was then added to the reaction mixture. After 24 h, it was quenched with ethyl vinyl ether (10 mL) and excess ether was removed by rotary evaporation. The resulting mixture was then purified and Me-ω-OHC18 the desired product was obtained from other by-products. Column chromatography was used for purification of unsaturated Me-ω-OHC18 using hexane/ethyl acetate=10:1.
The purified product from the metathesis reaction was then reduced over Raney nickel 2800 (slurry in water). The mixture was added into the hydrogenation vessel with 5 g Raney nickel and 200 ml excess ethanol. First, the reaction vessel was purged with nitrogen gas and then charged with hydrogen at 100 psi and 85° C. for 4 h. The reaction mixture was filtered using filter agent Celite®545 in a Buchner funnel. The product was then concentrated under pressure.
The synthesis of Me-ω-OHC18 is shown in the reaction scheme of
The structure of (ω-OHFA)s and (Me-ω-OHFA)s were confirmed by 1H NMR and mass spectroscopy, and is given in Table 2 along with their respective yield and purity values, determined by HPLC.
1H-NMR
2H, —CH2CH2COO), 1.56-1.53 (m, 2H, —CH2CH2OH),
The polymerization process to make P(Me-ω-OHFA)s and P(ω-OHFA)s is an equilibrium reaction and involved two phases; an esterification/transesterification phase (Phase 1) followed by the polycondensation phase (Phase 2). Polycondensation is a step-growth polymerization process, which involves a series of chemical reactions between bi-functional or multifunctional monomers to give polymeric condensates accompanied by the elimination of low molecular weight by-products (water, alcohol, etc.). This is an equilibrium reaction and required to push the reaction forward to obtain high molecular weights. This is achieved by using polycondensation catalysts, high temperatures (more than 200° C.) and high vacuum (below 0.1 mm of Hg). Catalysts are often used to obtain high molecular weight polyesters during polyesterification.
Zinc acetate and manganese acetate are some examples for esterification/transesterification catalysts used for the first polymerization phase. Titanium, antimony and tin-based compounds are the most reported catalysts used for the polycondensation (Phase 2), and at times, germanium has also be reported as a polycondensation catalyst, or combinations of the preceding. The order of the activities of various metallic catalyst was found to vary as Ti>Sn>Sb>Mn>Pb. The high catalytic activity, least environmental concerns and their acceptable prices for low-cost industrial processes favored the widespread use of Ti derived catalysts for polycondensation. Some non-limiting examples of catalysts used for polycondensation reactions include antimony trioxide, antimony triacetate, germanium oxide, tetrapropyl titanate, tetrabutyl titanate, tetrapropyl titanate, titanium butoxide, tetraisopropyl titanate, dibutyltin oxide or n-butyl hydroxytin oxide, all of which may be used alone or in combination. In some embodiments, titanium alkoxides such as titanium isopropoxide, may be used as the polycondensation catalyst.
Polymerization was conducted in a stainless steel reactor equipped with a mechanical stirrer, nitrogen inlet, gas outlet, a thermocouple and pressure gauge. The monomer (10 g) and a certain amount of catalyst solution (10 mg/mL Ti(OiPr)4 in 1-butanol) was transferred into the reactor. In the first polymerization phase (esterification/transesterification), the reaction mixture was initially heated at 150° C. for three hours with continuous stirring under N2 flow at atmospheric pressure. The temperature was subsequently raised and maintained at 180° C. for 2 hours, followed by another 2 hours at 200° C. under the same reaction conditions. Except for Me-ω-OHC9, because of its low thermal stability (˜130° C., as determined by thermogravimetric analysis), the reaction was initiated at 120° C. for an hour before applying elevated temperature cycles. In the second phase (polycondensation), traces of water/methanol were removed from the reaction medium to ensure high molecular weight products. This was achieved by (i) raising the temperature to 220° C. and maintaining it for 4 hours, (ii) placing the contents of the reactor under reduced pressure (<0.1 torr), (iii) increasing the speed of mixing. The polycondensation was further continued for another two hours at 220° C. under vacuum. Samples were measured in duplicates at regular intervals using GPC to determine the molecular weight and distribution.
To determine the optimal catalyst contents for P(ω-OHFA)s and P(Me-ω-OHFA)s, a series of polycondensation reactions were performed using varying catalyst amounts (50-500 ppm) and the evolution of molecular weight were analyzed using GPC. Polycondensation reactions were performed in duplicates for the optimal catalyst concentrations so as to determine the reproducibility of the experiments.
Optimization of the reaction time for polycondensation was carried out by increasing the phase 2 reaction time up to 6 hours at 220° C., for each individual catalyst concentration ranging from 50-500 ppm. The polyester molecular weight and distribution was measured every hour by GPC.
To optimize the reaction temperature, the phase 2 reaction temperature was increased from 220° C. to 230° C., 240° C. and 250° C. at regular intervals of 1 h during polymerization using optimal catalyst amounts. The evolution of polyester molecular weight and distribution was measured using GPC.
The general reaction scheme for the step-growth polymerization of P(Me-ω-OHFA)s and P(ω-OHFA)s is shown in
The structures of P(ω-OHFA)s and P(Me-ω-OHFA)s were analyzed by 1H NMR and FT-IR. 1H NMR (CDCl3 400 MHz) data of the P(ω-OHFA) and P(Me-ω-OHFA) are listed in Table 3.
1H NMR (CDCl3 400 MHz) data of the P(ω-OHFA)
1H NMR (CDCl3 400 MHz) δ (ppm)
2H, —CH2COO—), 4.06-4.09 (t, 2H, —CH2O—)
2H, —CH2COO—), 4.06-4.09 (t, 2H, —CH2O—)
2H, —CH2COO—), 4.06-4.10 (t, 2H, —CH2O—)
The chemical shift at 6=4.06-4.10 ppm for P(ω-OHFA)s and P(Me-ω-OHFA)s was assigned to the protons from the methylene group attached to the ester linkage (—CH2O—) formed as a result of polymerization. The absence of chemical shift at δ=3.50-3.70 ppm, corresponding to the protons from methylene group adjacent to the hydroxyl group in (ω-OHFA) and (Me-ω-OHFA)s monomers, suggests that the polymerization was carried out well. FT-IR, also confirmed the formation of the polyesters. As can be seen in
The 1H-NMR spectra were recorded on a Bruker Advance III 400 spectrometer (Bruker BioSpin MRI GmbH, Karlsruhe, Germany) at a frequency of 400 MHz, using a 5 mm BBO probe, and were acquired at 25° C. over a 16-ppm spectral window with a 1 s recycle delay, and 32 transients. NMR spectra were Fourier transformed, phase corrected, and baseline corrected. Window functions were not applied prior to Fourier transformation. Chemical shifts were referenced relative to residual solvent peaks.
FTIR spectra were acquired using a Thermo Scientific Nicolet 380 FTIR spectrometer (Thermo Electron Scientific Instruments LLC, Fitchburg, Wis.) fitted with a PIKE MIRacle™ attenuated total reflectance (ATR) system (PIKE Technologies, Madison, Wis., USA). The samples were placed onto the ATR crystal area and held in place by a pressure arm. The signal was acquired with the following parameters: scanning number=32; resolution=4.000; sample gain=8.0; mirror velocity=0.6329; and aperture=100.
Electrospray ionization mass spectrometry (ESI-MS) analysis was performed on the monomers using a QStar XL quadrupole time-of-flight mass spectrometer (AB Sciex, Concord, ON) equipped with an ion-spray source and a modified hot source-induced de-solvation (HSID) interface (Ionics, Bolton, ON). The ion source and interface conditions were adjusted as follows: ion spray voltage (IS=4500 V), nebulizing gas (GS1=45), curtain gas (GS2=45), de-clustering potential (DP=60 V) and HSID temperature (T=200° C.). Multiple-charged ion signals were reconstructed using the BioTools 1.1.5 software package (AB Sciex, Concord, ON).
The purity of (ω-OHFA)s and (Me-ω-OHFA)s were determined using High Performance Liquid Chromatography (HPLC). HPLC was carried on a Waters Alliance (Milford, Mass., USA) e2695 HPLC system fitted with a Waters ELSD 2424 evaporative light scattering detector. The HPLC system includes an inline degasser, a pump, and an auto-sampler. The temperature of the column (C18, 150 mm×4.6 mm, 5.0 μm, X-Bridge column, Waters Corporation, MA, USA) was maintained at 35° C. by a Waters Alliance column oven. The ELSD nitrogen flow was set at 25 psi with nebulization and drifting tube maintained at 12° C. and 55° C., respectively. Gain was set at 500. The mobile phase was chloroform: acetonitrile (50:50)v run for 30 min at a flow rate of 0.2 mL/min. 1 mg/mL (w/v) solution of sample in chloroform was filtered through single step filter vial (Thomson Instrument Company, CA, USA) and 0.5 mL of sample was passed through the C18 column by reversed-phase in isocratic mode. All solvents were HPLC grade and obtained from VWR International (Mississauga, ON, Canada).
Gel Permeation Chromatography (GPC) was used to determine the number average molecular weight (
GPC tests were carried out on a Waters Alliance (Milford, Mass., USA) e2695 pump, Waters 2414 refractive index detector and a Styragel HR5E column (5 mm). Chloroform was used as eluent with a flow rate of 0.5 mL/min. The sample was made with a concentration of 1 mg/mL, and the injection volume was 30 ml for each sample. Polystyrene (PS, #140) standards were used to calibrate the curve. All the GPC analyses were done in duplicate to assess the uncertainties.
n and PDI obtained at optimal catalyst concentration
n
a
a obtained from GPC.
The mechanism of the metal-alkoxide catalyst in self polycondensation of hydroxyl acids is still not well understood. Nonetheless, the observation of a maximum in plots of catalyst concentration versus
The variation of
n
a
a obtained from GPC.
The polycondensation step (Phase 2) at temperatures higher than 220° C. yielded polyesters with lower
The variation in
n
a
n
aobtained from GPC.
Knowledge of the reaction kinetics is required for the practical synthesis of P(ω-OHFA)s and P(Me-ω-OHFA)s. Assuming the rate of disappearance is first order in the reactive group concentration, the linear relationship between the number average degree of polymerization (X) and Phase 2 reaction time (t) is given by Equation 1,
n=1+k[A0]t (1)
where k is the reaction rate constant, and [A0] the concentration of the hydroxyl and acid/ester groups, [OH]═[COOH(OCH3)]=[A0] at the onset of Phase 2 polymerization at 220° C. S, is also related to the extent of reaction (p) by the well-known Carothers equation40 given by Equation 2,
The range of values for
As seen in
n=1+KC1/2 (3)
The equilibrium constant values obtained for all the polyesters are higher enough (KC≧104) to afford a degree of polymerization,
The use of different reactant systems, namely, ω-OHFAs and Me-ω-OHFAs yielded the same type of polyester, i.e., having the same [—(CH2)n—COO—] repeating monomer unit. The polyesters with the best chain distribution was obtained by the polycondensation of Me-ω-OHFAs at 220° C. using the optimal catalyst amounts (300 ppm), as is revealed by Tables 4, 5 and 6. The relatively higher
As a general recap, a group of ω-hydroxy fatty acid (ω-OHFA) [HO—(CH2)n—COOH] and ester (ω-Me-OHFA) [HO—(CH2)n—COOCH3] homologues with medium (n=8 and 12) and long (n=17) methylene chains, suitable for making degradable thermoplastic polyesters were successfully produced from unsaturated fatty acids, unsaturated fatty acid methyl esters, and unsaturated fatty alcohols, derived from natural oils. The methyl ester homologues having n=8 and 12 were synthesized from methyl oleate, and erucic acid, respectively, by ozonolysis—reduction reactions at the fatty acid double bonds. Their subsequent saponification gave the acid homologues, namely 9-hydroxynonanoic acid (ω-OHC9), and 13-hydroxytridecanoic acid (ω-OHC13), respectively. The long chain homologue (n=17) 18-hydroxyoctadecanoic acid (ω-OHC18) and methyl 18-hydroxyoctadecanoate (ω-Me-OHC18) were obtained by cross-metathesis of methyl oleate and oleyl alcohol using Grubbs catalyst in good yields and purity.
The equilibrium melt polycondensation of the (ω-OHFA)s and (ω-Me-OHFA)s was investigated for the purpose of understanding the optimal reaction conditions favorable to achieve polymerization products with desired molecular mass and distribution. For P(ω-OHFA)s and P(ω-Me-OHFA)s, the molecular chain size (
P(ω-OHFA)s and P(ω-Me-OHFA)s obeyed first order kinetics for the last 1-2% of polymerization. The acid homologues (Me-ω-OHFA)s were preferred over the ester derivatives for their ease of preparation of the monomers. The equilibrium and kinetics studies suggested that the polymerization of the P(ω-Me-OHFA)s proceeded more easily and at a faster rate and gave polyesters with higher molecular weights and better distribution than P(ω-OHFA)s.
The effects of structural and molecular parameters on the thermal and mechanical properties of poly-hydroxyesters, namely poly(ω-hydroxynonanoate), P(Me-ω-OHC9) (n=8), poly(ω-hydroxytridecanoate), P(Me-ω-OHC13) (n=12), and poly(ω-hydroxyoctadecanoate), P(Me-ω-OHC18) (n=17), were analyzed. The corresponding polymers of these materials were obtained by polycondensation of certain of methyl-ω-hydroxyl fatty ester monomers (Me-ω-OHFA)s [HO—(CH2)n—COOCH3], as previously described.
Ti(IV) isopropoxide and 1-butanol were purchased from Sigma-Aldrich. The monomers (Me-ω-OHC9) (96.5% purity), (Me-ω-OHC13) (97% purity), and (Me-ω-OHC18) (97% purity) were synthesized in our laboratories. The detailed synthesis of the monomers was described previously. A series of P(Me-ω-OHFA)s were prepared with the number average molecular weights,
The polyesterification was conducted in a stainless steel reactor equipped with a mechanical stirrer, nitrogen inlet, gas outlet, a thermocouple and pressure gauge. The monomer (10 g) and optimal amount of catalyst solution (10 mg/mL Ti(OiPr)4 in 1-butanol) was transferred into the reactor. The reaction mixture was initially heated at 150° C. for three hours with continuous stirring under N2 flow at atmospheric pressure. The temperature was subsequently raised and maintained at 180° C. for 2 hours, followed by another 2 hours at 200° C. under the same reaction conditions.
Except for (Me-ω-OHC9), because of its relatively lower thermal stability (˜130° C., determined from TGA analysis), the reaction was initiated at 120° C. for one hour before applying elevated temperature cycles. Traces of methanol were removed from the reaction medium by heating the mixture at 220° C. under reduced pressure (<0.1 torr). Desired molecular weights were obtained by maintaining the above reaction conditions for optimal reaction times, which varied between 1 to 4 hours. The solid samples were melt pressed to make films at a controlled cooling rate of 5° C./minute on a Carver 12 ton hydraulic heated bench press (Model 3851-0, Wabash, Ind., USA).
The structures of P(Me-ω-OHFA)s were analyzed by 1H NMR spectroscopy. The spectra were recorded on a Bruker Avance III 400 spectrometer (Bruker BioSpin MRI GmbH, Karlsruhe, Germany) at a frequency of 400 MHz. Deuterated chloroform (CDCl3), which has a chemical shift of 7.26 ppm was used as a solvent. The chemical shifts for P(Me-ω-OHFA)s were referenced relative to residual solvent peaks.
Gel Permeation Chromatography (GPC) was used to determine the number (
DSC analysis was carried out under a dry nitrogen gas atmosphere on a Q200 (TA instrument, Newcastle, Del., USA) following the ASTM E1356-03 standard procedure. The solid sample (5.0-6.0 mg) was first equilibrated at 0° C. and heated to 130° C. at a constant rate of 3.0° C./min (first heating cycle). The sample was held at that temperature for 10 minute to erase the thermal history, then cooled down to −90° C. with a cooling rate of 3° C./minute and subsequently reheated to 130° C. at the same rate (second heating cycle). During the heating process, measurements were performed with modulation amplitude of ±1° C. at every 60 seconds.
Thermogravimetric Analysis (TGA) of the synthesized polyesters was carried out on a Q500 (TA instrument, Newcastle, Del., USA) following the ASTM D3850-94 standard procedure. Samples of ˜10 mg were heated from room temperature to 600° C. under dry nitrogen at a constant heating rate of 10° C./minute.
Viscoelastic behavior of P(Me-ω-OHFA)s was studied by performing dynamic temperature sweeps in a dynamic mechanical analyzer (DMA Q800, TA instrument) equipped with a liquid nitrogen cooling system. Rectangular polymer films (17.5 mm×12 mm×0.6 mm) were measured in dual cantilever and three points bending modes at a frequency of 1 Hz and fixed oscillation displacement of 15 μm, following the ASTM D7028 standard procedure. The samples were heated under a constant rate of 1° C./min over a temperature range of −90° C. to 60° C.
The static mechanical properties of the polymer films were determined at room temperature using a Texture Analyzer (TA HD, Texture Technologies Corp, NJ, USA) equipped with a 2-kg load cell. The measurements were performed following the ASTM D882 standard procedure. The sample was stretched at a rate of 5 mm/min from a gauge of 35 mm.
Wide-angle X-ray diffraction (WAXD) was carried out at room temperature (˜22° C.) on an EMPYREAN diffractometer system (PANalytical, The Netherlands) equipped with a Cu-Kα radiation source (λ=1.540598 Å) and a PIXcel-3D™ area detector. The WAXD patterns were recorded at 45 kV and at 40 mA. The 2θ-scanning range was from 3° to 90°. 3313 points were collected in 45 min in this process. The data were processed and analyzed using the Panalytical's X′Pert HighScore V3.0 software. The degree of crystallinity was estimated according to a well-established procedure. The percentage degree of crystallinity (XC) is given by equation (4),
where AC is the area under the resolved crystal diffraction peaks and AA, the area of the amorphous contribution halo.
The structures of P(Me-ω-OHFA)s were analyzed by 1H NMR spectroscopy. Generally, the peaks at 3.50-3.70 ppm corresponding to protons from the end methyl group and the hydrogen from the α-proton to hydroxyl group which are present in the monomers did not appear in the spectrums of the P(Me-ω-OHFA)s. The spectrums of P(Me-ω-OHFA)s also demonstrated a new peak at 4.06-4.10 ppm, assignable to the protons from the methylene group attached to the ester linkage formed as a result of polymerization. 1H NMR (CDCl3 400 MHz) data of the P(Me-ω-OHFA)s are listed in Table 6A.
1H NMR (CDCl3 400 MHz) data of the P(Me-ω-OHFA)s.
P(Me-ω-OHC9)
1H NMR (CDCl3 400 MHz) δ (ppm): 1.20-1.34
P(Me-ω-OHC13)
1H NMR (CDCl3 400 MHz) δ (ppm): 1.29-1.31
P(Me-ω-OHC18)
1H NMR (CDCl3 400 MHz) δ (ppm): 1.28-1.33
The number (
w
n
The crystalline structure of the P(Me-ω-OHFA) samples was investigated by wide-angle X-ray diffraction (WAXD).
The variation of the corresponding d-spacing of the crystal peaks with number of (CH2) groups (n) are presented in
The WAXD patterns obtained for P(Me-ω-OHFA)s are reminiscent of that obtained for melt crystallized polyethylene (PE), indicating similar crystal structures. The sharp diffraction peaks observed in the WAXD patterns of P(Me-ω-OHFA)s (
The degree of crystallinity, XC, of the P(Me-ω-OHFA)s as estimated from WAXD, were in the 50% to 78% range (Table 8).
Onset, Ton, offset, Toff, peak temperature of melting, Tm, and enthalpy of melting, ΔHm obtained from second heating cycle, and degree of crystallinity, XC estimated from WAXD. The uncertainties attached to the characteristic temperatures, enthalpies and degree of crystallinity are better than 0.5° C., 8 J/g and 5% respectively.
The DSC thermograms of P(Me-ω-OHC9)28.4k (n=8), P(Me-ω-OHC13)30.3k (n=12), and P(Me-ω-OHC18)34.7k (n=17) obtained during the second heating cycle are shown in
As seen from Table 8, Tm of the P(Me-ω-OHFA)s increased significantly with n. The large increase in Tm(˜20° C.) when the number of methylene groups was increased from n=8 to 17 indicates clearly that longer [—(CH2)n—COO—] monomer units form thermodynamically more stable, thicker crystals upon cooling, which melt at higher temperatures.
For semi-crystalline polymers, the three key physical factors determining Tm are (i) chain stiffness (ii) inter-chain cohesive forces, and (iii) inter-chain packing efficiency. In the case of polyesters, the concentration of flexible —OCO groups in the chain backbone determines the molecular chain stiffness. The polar ester groups also contribute favorably to the inter-chain attractive cohesive forces, and thereby promote crystallization. Any preferred conformational effect favoring the packing of aliphatic methylene chains by van der Waals attraction is also expected to contribute to the polyester crystallinity.
The minimum observed in Tm versus n curve (
Viscoelastic response, obtained by DMA was used to classify the various solid state transitions, including glass transition.
The amorphous glass-rubber transition (Tg) is indicated prominently by a well-developed relaxation process. Tg is marked by an abrupt decrease of ˜3 GPa in E′ observable between −30° C. and 0° C. (
Aliphatic polyesters generally exhibit three relaxations where the elastic storage modulus (E′) changes rapidly with temperature, and maxima occur in the mechanical loss factor (E′) and tan δ curve. These transitions, in their descending order, i.e., the melting temperature, glass transition and subglass transition are known as the α, β, and γ transitions, respectively. The α-transition corresponding to the melting of the crystal phase of the P(Me-ω-OHFA) samples did not appear in
The Tg of P(Me-ω-OHFA)s ranged from −30° C. to −19° C. (Table 9), indicating that the amorphous regions remain in the ductile state at temperatures very favorable for a large set of high end applications, especially at service temperatures which are required for biomedical polymers. The location of Tg is also relevant for the fabrication of P(Me-ω-OHFA)s with desired crystallinities. Since crystallization is limited to the temperature range between Tg and Tm, and that a maximum rate of crystallization is expected between these two temperatures, the thermal history between Tg and Tm while processing influence the extent of crystallinity in P(Me-ω-OHFA)s.
−19 ± 0.9
Aliphatic polyesters as well as linear PE are non-quenchable to their amorphous states (XC=0%), and are generally categorized into medium (XC=30-60%) and highly crystalline (XC=60-80%) classes of polymers for investigating their relaxation behavior. In linear PE, the high degree of crystallinity obscure the molecular motions due to the amorphous chains and therefore the assignment of Tg has long been a controversial topic. Based on the thermal expansion data for linear PE, recent studies established a linear relationship between Tg and XC and suggested that Tg is determined by PE crystalline fraction.
The fact that Tg is dependent on the technique employed for its determination as well as the thermal processing conditions (rate of cooling or heating), dictate that it is rather described by a range of temperatures. However, the plot of our Tg data with those reported in the literature for the different homologues, showed a clear trend. The variation of Tg of polyesters of the [—(CH2)n—COO—] homologous series shown in
Furthermore, Tg/Tm of the P(Me-ω-OHFA)s varied between 0.6-0.7 (Table 9) in very good agreement with the empirical Boyer-Beaman rule (Equation 5),
T
g=(0.5 to 0.7)×Tm (5)
For isothermal crystallization, Tg/Tm is directly correlated to the maximum attainable crystalline fraction, XC, max, which is a rough indicator of intrinsic crystallizability of polymers.
A similar approach based on the balance of competing effects can be brought forward to explain both Tg and Tm in regards to chain length of the monomeric unit since the same factors, namely, chain stiffness and inter-chain cohesive forces, affecting Tm also influence Tg. For the short chain polyesters (n=1 to 5), the observed initial decrease of Tg with increasing n (
The thermal decomposition of P(Me-ω-OHFA) samples was investigated by TGA.
The onset degradation temperature, defined at 1% weight loss (Td(1)), and the temperature at 50% weight losses (Td(50)) are listed in Table 3. Td(1) is a direct measure of thermal stability, and is a crucial parameter for the melt-processing of thermoplastics. The noticeable effects of
Td(50) can be related to the chemical structure of the polymer. Recent studies based on molar additive group contribution methods, established an empirical relationship between the temperature at half decomposition (Td(50)) of the polymer and the [—(CH2)n—COO—] repeat unit molecular weight (M) through a molar thermal decomposition function (Yd(50)) (Equation 6),
As is the case with aliphatic polyesters, Td(50) values of the P(Me-ω-OHFA)s coincided with their maximum decomposition temperature (Td(max), from DTG). The actual Td(max) values are of major practical importance as the aliphatic polyesters of the ([—(CH2)n—COO—]) homologous series are rarely intended for high temperature applications. Td(max), however, being independent of molecular effects, is a good indicator of the effect of n on the thermal decomposition.
P(Me-ω-OHFA)s exhibited a stress-strain behavior typical of high modulus and brittle plastics, irrespective of
The various mechanical properties of the P(Me-ω-OHFA)s are listed in Table 10. The stiffness of P(Me-ω-OHFA)s, as represented by Young's modulus (YM), decreased with increasing
Several studies have indicated that the degree of crystallinity is the primary factor affecting YM of semi-crystalline polymers, including linear PE.
YM of the P(Me-ω-OHFA)s, increased linearly with XC (solid lines in
The behavior of YM of the P(Me-ω-OHFA)s is also consistent with the trend exhibited by other long chain polyesters such as P(Me-ω-OHFC14) (n=13) and PPDL (n=14) reported in the literature. Interestingly, when the data from the literature is included, the general trend suggested by YM versus XC (
This type of correlation (represented in
It is interesting to note (Table 10) that elongation at break (EB) and ultimate strength (TS) of P(Me-ω-OHC9)28.4k, P(Me-ω-OHC13)30.3k and P(Me-ω-OHC18)34.7k, which have similar
As a general recap, renewable poly(ω-hydoxyfatty ester)s (P(Me-ω-OHFA)s) with medium (n=8, 12) and long methylene chain lengths (n=17) and varying molecular weight (
All the P(Me-ω-OHFA)s presented an orthorhombic crystal phase reminiscent of linear PE with crystallinity (XC) depending strongly on
The variations of Tm and Tg of the P(Me-ω-OHFA)s, including data of polyesters of the [—(CH2)n—COO—] homologous series mined from the literature, as a function of n are remarkably similar. After an initial steep decrease observed for the short aliphatic polyesters (n≦5), both Tm and Tg reached a minimum then increased gradually with n for the medium chains (n=5-13) and reached a plateau for longer chain polymers (n≦13). Similar arguments based on the balance of competing effects were invoked to explain this trend. The variation of Tm is attributable to the competition between the cohesive energies due to the ester groups, which decrease with increasing n, and the chain stiffness as well as inter-chain packing efficiencies, which increases with increasing n, as the polymer chains become more “PE-like”. The trend observed for Tg is the result of a competition between the contributions of the amorphous inter-chain cohesive energies, the topological constraints imposed on the amorphous chains due to predominant crystallization effects from the methylene group and their impact on the “magnitude” of the segmental motions of the amorphous polyester chains.
The thermal stability of the P(Me-ω-OHFA)s, as directly measured by the onset degradation temperature (Td(1)), was noticeably affected by
Medium and long chain polyesters made from renewable feedstock such as the P(Me-ω-OHFA)s of the present study have a great potential for many targeted industrial applications, particularly those requiring biodegradability and biocompatibility such as biomedical implants and scaffolds. Furthermore, the predictive structure-relationships established in this study can be used to easily custom engineer such materials.
Co-Polymerization of Certain P(Me-ω-OHFA)s:
The present effort also focused on the preparation and solid-state characterization of certain copolyesters, such as poly(ω-hydroxy nonanoate/ω-hydroxy tridecanoate) [—(CH2)13—COO—/—(CH2)8—COO—]x random co-polyesters derived from vegetable oil. Poly(ω-hydroxy nonanoate/ω-hydroxy tridecanoate) were obtained by the melt polycondensation of methyl-13-hydroxytridecanoate (Me-ω-OHC13) and methyl 9-hydroxynonanoate (Me-ω-OHC9) synthesized from unsaturated fatty acids. The various physical properties of co-polyesters were investigated as a function of co-polyester composition.
Ti(IV) isopropoxide (99.99% purity), 1-butanol (99.98% purity) and [(Methoxycarbonyl)methyl]phosphonic acid diethyl ester (MDPA) (99.99% purity) were purchased from Sigma-Aldrich. The reagents were used without further purification. The monomers (Me-ω-OHC9) (96.5% purity), (Me-ω-OHC13) (97% purity) were synthesized in our laboratories.
Poly(ω-hydroxy nonanoate/ω-hydroxy tridecanoate) P(-Me-ω-OHC13-/-Me-ω-OHC9-) random copolyesters with varying molar compositions were prepared from (Me-ω-OHC9) and (Me-ω-OHC13) using a two-step melt condensation procedure. The co-polymerization was conducted in a stainless steel reactor equipped with a mechanical stirrer, nitrogen inlet, gas outlet, a thermocouple, and pressure gauge. 50 mmol of the monomer mixture with varying (Me-ω-OHC9): (Me-ω-OHC13) ratios were mixed with 300 ppm of catalyst solution (10 mg/mL Ti(OiPr)4 in 1-butanol) in the reactor. The reaction mixture was initially heated at 130° C. for 1 hour with continuous stirring under N2 flow at atmospheric pressure. The temperature was subsequently raised and maintained at 160° C. for 2 hours, followed by another 3 hours at 180° C. under the same reaction conditions. MDPA (0.005 moles/moles of ester monomer) was added at this stage. The reaction mixture was further heated at 210° C. under reduced pressure (<0.1 torr) for 1 h followed by another 30 minutes at 220° C. so as to remove traces of methanol by-product. The solid samples were molded to films on a Carver 12-ton hydraulic heated bench press (Model 3851-0, Wabash, Ind., USA) at a controlled cooling rate of 5° C./minute. Selected copolymer compositions were further polymerized at 230° C. for 30 minutes to increase the PDI so that films suitable for tensile analysis could be molded.
1H NMR was used to determine the co-polyester structure and molar compositions. The spectra were recorded at a Larmor frequency of 400 MHz, using a Varian Unity 400 NMR spectrometer (Varian, Inc., Walnut Creek, Calif., USA). Gel Permeation Chromatography (GPC) was used to determine the number average molecular weight (Mn), weight-average molecular weight (Mw) and polydispersity index (the distribution of molecular mass, PDI=Mw/Mn). GPC tests were carried out on a Waters Alliance (Milford, Mass., USA) e2695 pump, Waters 2414 refractive index detector and a Styragel HR5E column (5 μm). Chloroform was used as eluent with a flow rate of 0.5 mL/min. The sample was made with a concentration of 2 mg/mL, and the injection volume was 30 ul for each sample. Polystyrene (PS, #140) Standards were used to calibrate the curve.
Calorimetric studies of the synthesized co-polymers were performed on a DSC Q200 (TA instrument, Newcastle, Del., USA) following the ASTM E1356-03 standard procedure under a dry nitrogen gas atmosphere. The sample was first heated to 110° C. (referred to as the first heating cycle), and held at that temperature for 5 min to erase the thermal history; then cooled down to −50° C. with a cooling rate of 5° C./minute. The sample was heated again (referred to as the second heating cycle) with a constant heating rate of 3° C./minute from −50° C. to 160° C. During the second heating cycle, measurements were performed with modulation amplitude of 1° C./minute and a modulation period of 60 seconds.
Thermogravimetric Analysis was carried out using a TGA Q500 (TA instrument, Newcastle, Del., USA.). Samples were heated from room temperature to 600° C. under dry nitrogen at constant heating rate of 10° C./minute.
Viscoelastic behavior of the PEUs was studied by performing dynamic temperature sweeps in a dynamic mechanical analyzer (TA instrument, DMA Q800) equipped with a liquid nitrogen cooling system. Rectangular polymer films (17.5 mm×12 mm×0.6 mm) were analyzed in a dual cantilever-bending mode following the ASTM D7028 standard procedure at a frequency of 1 Hz and fixed oscillation displacement of 15 μm. The samples were heated under a constant rate of 1° C./minute over a temperature range of −90° C. to 80° C.
The static mechanical properties of the synthesized polymer films were determined at room temperature using a Texture Analyzer (Texture Technologies Corp, NJ, USA) following the ASTM D882 procedure. The sample was stretched at a rate of 5 mm/minute from a gauge of 35 mm.
The crystalline structure of co-polyesters was examined by wide-angle X-ray diffraction (WAXD) on an EMPYREAN diffractometer system (PANanalytical, The Netherlands) equipped with a filtered Cu-Kα radiation source (λ=1.540598 Å) and a PIXcel3D area detector. Copolyester samples were crystallized from the melt at a controlled cooling rate of 5° C./minute. The scanning range was from 3.3° to 35° (2θ) with a step size of 0.013°; 2414 points were collected in this process. The deconvolution of the spectra, and data analysis were performed using PANanalytical's X'Pert HighScore 3.0.4 software. The degree of crystallinity was estimated according to a well-established procedure. The percentage degree of crystallinity (XC) is given by equation (7),
where AC is the area under the resolved crystal diffraction peaks and AA, the area of the amorphous contribution halo.
The general reaction scheme for the polycondensation of (Me-ω-OHC13) and (Me-ω-OHC9) monomers is shown in
where a′-d′, a″-d″ and a-d also represent the areas of corresponding peaks for P(Me-ω-OHC9), P(Me-ω-OHC13) and the 50/50 w/w co-polyester, respectively (
The molecular weight distribution for homopolyesters and P(-Me-ω-OHC13-/-Me-ω-OHC9-) copolyesters were determined by GPC (Table 11). The co-polyesters exhibited comparable molar masses in the range of 9000-19000 g/mol (
w
n
Melt transition behavior of random P(-Me-ω-OHC13-/-Me-ω-OHC9-) co-polyesters are described herein. The heating and cooling thermograms for the copolymer systems are shown in
The variation of the d-spacing as a function of co-polyester composition is presented in
The TGA derivative (DTG) of the homopolymers (A1 and A7) as well as the P(-Me-ω-OHC13-/-Me-ω-OHC9-) co-polymers (A2-A6) displayed (
The onset degradation temperature, defined at 5% weight loss (To)), and the temperature at maximum degradation rate (Td(max)) are listed in Table 13. The onset degradation temperature is a direct measure of thermal stability, and is a crucial parameter for the melt-processing of thermoplastics. The noticeable effect of copolymer composition on Td(5) and Td(max) is illustrated in
Viscoelastic response, obtained by DMA was used to classify the glass transition temperature of co-polyesters.
DMA analysis of the co-polyesters revealed a sharp single glass transition marked by an abrupt decrease of ˜3 GPa in elastic modulus observable between −50 and 0° C. as well as pronounced peaks in tan 6 curves (
The glass transition temperature (Tg) of the co-polyesters determined from the peak value of tan δ curves are listed in Table 3. The Tg of copolyesters are in the range of −36° C. to −25° C. (Table 13) indicating that the amorphous regions remain in the ductile state at temperatures very favorable for a large set of high end applications, especially at service temperatures which are required for biomedical polymers. Tg of the copolyester decreased linearly with increasing (Me-ω-OHC9) comonomer content (
Low molecular weight P(-Me-ω-OHC13-/-Me-ω-OHC9-) co-polyester samples (A1-A7 with
w
n
As a general recap, renewable poly(ω-hydroxy nonanoate/ω-hydroxy tridecanoate) [P(-Me-ω-OHC13-/-Me-ω-OHC9-)] random co-polyesters with varying ratios of (Me-ω-OHC13):(Me-ω-OHC9) comonomer units were successfully prepared by melt polycondensation of ω-hydroxy fatty ester monomers derived from vegetable oil. The thermal stability, transition behavior, mechanical properties, and crystallinity, examined by TGA, DSC, DMA and tensile analysis, and WAXD, respectively, were related to the composition of the co-polyesters. Investigation of structure-function relationships revealed composition dependent melting, glass transition and thermal decomposition behavior for P(-Me-ω-OHC13-/-Me-ω-OHC9-)s. These co-polyester systems presents excellent examples of thermally stable random copolymers where the density of hydrolyzable ester groups can be freely changed with varying composition without inducing dramatic changes to crystallinity and the related physical properties.
The above polyesters and copolyesters may be utilized independently and/or incorporated into various formulations and used as functional ingredients in dimethicone replacements, laundry detergents, fabric softeners, personal care applications, such as emollients, hair fixative polymers, rheology modifiers, specialty conditioning polymers, surfactants, UV absorbers, solvents, humectants, occlusives, film formers, or as end use personal care applications, such as cosmetics, lip balms, lipsticks, hair dressings, sun care products, moisturizer, fragrance sticks, perfume carriers, skin feel agents, shampoos/conditioners, bar soaps, hand soaps/washes, bubble baths, body washes, facial cleansers, shower gels, wipes, baby cleansing products, creams/lotions, and antiperspirants/deodorants. The polyesters and copolyesters may also be incorporated into various formulations and used as functional ingredients in lubricants, functional fluids, fuels and fuel additives, additives for such lubricants, functional fluids and fuels, plasticizers, asphalt additives, friction reducing agents, antistatic agents in the textile and plastics industries, flotation agents, gelling agents, epoxy curing agents, corrosion inhibitors, pigment wetting agents, in cleaning compositions, plastics, coatings, adhesives, skin feel agents, film formers, rheological modifiers, release agents, conditioners dispersants, hydrotropes, industrial and institutional cleaning products, floor waxes, oil field applications, gypsum foamers, sealants, agricultural formulations, enhanced oil recovery compositions, solvent products, gypsum products, gels, semi-solids, detergents, heavy duty liquid detergents (HDL), light duty liquid detergents (LDL), liquid detergent softeners, antistat formulations, dryer softeners, hard surface cleaners (HSC) for household, autodishes, rinse aids, laundry additives, carpet cleaners, softergents, single rinse fabric softeners, I&I laundry, oven cleaners, car washes, transportation cleaners, drain cleaners, defoamers, anti-foamers, foam boosters, anti-dust/dust repellants, industrial cleaners, institutional cleaners, janitorial cleaners, glass cleaners, graffiti removers, concrete cleaners, metal/machine parts cleaners, pesticides, agricultural formulations and food service cleaners, plasticizers, asphalt additives and emulsifiers, friction reducing agents, film formers, rheological modifiers, biocides, biocide potentiators, release agents, household cleaning products, including liquid and powdered laundry detergents, liquid and sheet fabric softeners, hard and soft surface cleaners, sanitizers and disinfectants, and industrial cleaning products, emulsion polymerization, including processes for the manufacture of latex and for use as surfactants as wetting agents, and in agriculture applications as formulation inerts in pesticide applications or as adjuvants used in conjunction with the delivery of pesticides including agricultural crop protection turf and ornamental, home and garden, and professional applications, and institutional cleaning products, oil field applications, including oil and gas transport, production, stimulation and drilling chemicals and reservoir conformance and enhancement, organoclays for drilling muds, specialty foamers for foam control or dispersancy in the manufacturing process of gypsum, cement wall board, concrete additives and firefighting foams, paints and coalescing agents, paint thickeners, or other applications requiring cold tolerance performance or winterization (e.g., applications requiring cold weather performance without the inclusion of additional volatile components).
The foregoing detailed description and accompanying figures have been provided by way of explanation and illustration, and are not intended to limit the scope of the invention or the appended claims. Many variations in the present embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the invention and their equivalents.
A claim of priority for this application under 35 U.S.C. §119(e) is hereby made to the following U.S. provisional patent application: U.S. Ser. No. 61/872,594 filed Aug. 30, 2013; and this application is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61872594 | Aug 2013 | US |
