Biodegradable polymers based on renewable resources. IV. Enzymatic degradation of polyesters composed of 1,4:3.6‐dianhydro‐D‐glucitol and aliphatic dicarboxylic acid moieties

Enzymatic degradation of a series of polyesters prepared from 1,4:3.6‐dianhydro‐D ‐glucitol (1) and aliphatic dicarboxylic acids of the methylene chain length ranging from 2 to 10 were examined using seven different enzymes. Enzymatic degradability of these polyesters as estimated by water‐soluble total organic carbon (TOC) measurement is dependent on the methylene chain length (m) of the dicarboxylic acid component for most of the enzymes examined. The most remarkable substrate specificity was observed for Rhizopus delemar lipase, which degraded polyester derived from 1 and suberic acid (m = 6) most readily. In contrast, degradation by Porcine liver esterase was nearly independent of the structure of the polyesters. Enzymatic degradability of the polyesters based on three isomeric 1,4:3.6‐dianhydrohexitols and sebacic acid was found to decrease in the order of 1, 1,4:3.6‐dianhydro‐D ‐mannitol (2), and 1,4:3.6‐dianhydro‐L ‐iditol (3). Structural analysis of water‐soluble degradation products formed during the enzymatic hydrolysis of polyester 5g derived from 1 and sebacic acid has shown that the preferential ester cleavage occurs at the O(5) position of 1,4:3.6‐dianhydro‐D ‐glucitol moiety in the polymer chain by enzymes including Porcine pancreas lipase, Rhizopus delemar lipase, and Pseudomonas sp. lipase. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 338–346, 2000     

Synthesis of 1,3‐benzodioxole end‐functionalized polymers via reversible addition–fragmentation chain transfer polymerization

Reversible addition–fragmentation chain transfer (RAFT) polymerization of styrene was carried out in the presence of a novel RAFT reagent, bearing 1,3‐benzodioxole group, benzo [1,3]dioxole‐5‐carbodithioic acid benzo [1,3]dioxol‐5‐ylmethyl ester (BDCB), to prepare end‐functionalized polystyrene. The polymerization results showed that RAFT polymerization of styrene could be well controlled. Number–average molecular weight (M_n(GPC)) increased linearly with monomer conversion, and molecular weight distributions were narrow (M_w/M_n < 1.4). The successful reaction of chain extension and analysis of ¹H NMR spectra confirmed the existence of the functional 1,3‐benzodioxole group at the chain‐end of polystyrene. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3535–3539, 2006     

Chain extension of polybutylene adipate and polybutylene succinate with adipoyl‐ and terephthaloyl‐biscaprolactamate

HO‐terminated polybutylene adipate (HO‐PBA‐OH) with molecular weight from 1040 to 3540 and HO‐terminated polybutylene succinate (HO‐PBS‐OH) with intrinsic viscosity of 0.37 dL/g were synthesized through melt condensation polymerization from adipic acid or succinic acid with excess of butanediol. Chain extension of HO‐PBA‐OH or HO‐PBS‐OH with adipoyl biscaprolactamate and terephthaloyl biscaprolactamate was carried out at 200–240°C under reduced pressure. At the optimal conditions, chain‐extended PBA with M_n up to 50,700, and M_w up to 125,700 was synthesized, and the chain‐extended PBS with intrinsic viscosity of 1.25 dL/g was obtained. Meanwhile, p‐toluenesulfonic acid, SnCl₄ and zinc acetylacetonate catalyzed chain‐extending reaction of HO‐PBA‐OH and HO‐PBS‐OH was also studied. The chain‐extended polyesters were characterized by IR spectra, ¹H‐NMR spectra, and differential scanning calorimetry (DSC). The chain extension proceeds through the elimination of caprolactam rings in the chain‐extenders, the adipoyl groups or the terephthaloyl groups couple the hydroxyl‐terminated polyesters together and make the molecular weight of PBA or PBS increased, whether the acid catalyst such as p‐toluenesulfonic acid was present or not. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Chopping high‐molecular weight poly(1,4‐butylene carbonate‐co‐aromatic ester)s for macropolyol synthesis

The condensation of a mixture of dimethyl carbonate and phthalate derivatives with 1,4‐butanediol (BD), catalyzed by sodium alkoxide, generated high‐molecular weight poly(1,4‐butylene carbonate‐co‐aromatic ester)s with molecular weights (M_n) of 50–120 kDa. The subsequent addition of polyols [BD, glycerol propoxylate, 1,1,1‐tris(hydroxymethyl)ethane, or pentaerythritol] chopped these high‐molecular weight polymers to afford macrodiols or macropolyols with facile control of their molecular weights (M_n, 2000–3000 Da) and unique chain topological compositions. Macropolyols prepared by chopping poly(1,4‐butylene carbonate‐co‐terephthalate) were waxy in nature, whereas those containing isophthalate and phthalate units were oily. The macropolyols synthesized by this chopping method may have potential applications in the polyurethane industry. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43754.     

Study on biodegradable polymer materials based on poly(lactic acid). I. Chain extending of low molecular weight poly(lactic acid) with methylenediphenyl diisocyanate

Methylenediphenyl diisocyanate (MDI) was used as the chain extender for low molecular weight poly(lactic acid) (PLA) to produce high molecular weight biodegradable polymer material with a better heat resistance. PLA prepolymer with a number‐average molecular weight (M_n) of 5800 and a weight‐average molecular weight (M_w) of 9800 was produced by direct polycondensation using stannous octoate as the catalyst. After 40 min of chain extension at 175°C, the resulting polymer had a M_n of 15,000 and a M_w of 57,000. The glass transition temperature (T_g) of the low molecular weight PLA prepolymer was 48.6°C. After chain extension, the T_g of the resulting polymer was raised to 67.9°C, as determined by DSC. DMA results also indicate that the heat resistance was improved by the chain extension. The DSC spectrum and X‐ray diffraction pattern of annealed samples showed that both the crystallinity and rate of crystallization of PLA were lowered by chain‐extension reaction due to the formation of branched molecular structure. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2546–2551, 1999     

Synthesis of graft polyesters by ring-opening copolymerization of epoxy-terminated poly(ethylene glycol) with acid anhydrides

The copolymerization of epoxy-terminated poly(ethylene glycol methyl ether) (CH₃PEG–epoxide) with phthalic anhydride catalyzed by tertiary amines was performed in o-dichlorobenzene at 100°C to prepare the PEG graft polyester. 4-Dimethylaminopyridine was the most favorable catalyst to give the graft polyester with relatively high molecular weight. The acidity of the reaction solution decreased and M _n of the graft polyesters increased with reaction time. The CH₃PEG/phthalic acid ratio of the products was little affected by the kind of solvent and the reaction temperature above 100°C, but M _n increased with lowering the polarity of solvents and with raising the temperature. Other acid anhydrides, including maleic, succinic, tetrahydrophthalic, and pyromellitic anhydride, could be copolymerized with CH₃PEG–epoxide. The number of branched CH₃PEG chains was controlled by the mixing of low molecular weight epoxide such as n-butyl glycidyl ether. CH₃PEG component of the graft copolymers melted and crystallized at lower temperature than the raw CH₃PEG because of the restriction on the trunk polyester chain.     

Preparation and characterization of some new unsaturated polyesters based on 3,6‐bis(methoxymethyl)durene

A series of unsaturated polyester resins based on 3,6‐bis(methoxymethyl)durene with different diacids or anhydrides, namely, phthalic anhydride, maleic anhydride, and succinic acid, and different glycols, namely, 1,2‐propylene glycol, triethylene glycol, 1,4‐cyclohexane diol, and 3,6‐bis(benzyloxymethyl)durene, were prepared. Infrared and nuclear magnetic resonance spectra were used to characterize the unsaturated polyester resins obtained qualitatively and quantitatively. The average‐number molecular weight (M^?_n) was determined by end‐group analysis. These polyesters were found to cure with styrene at room temperature. The thermal behavior of the styrenated polyesters was studied via thermogravimetrical analysis and differential scanning calorimetry (TGA and DSC). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3388–3398, 2001     

Synthesis of aliphatic polyesters by a chain‐extending reaction with octamethylcyclotetrasilazane and hexaphenylcyclotrisilazane as chain extenders

Aliphatic HO-terminated polyesters such as poly(diethylene glycol adipate) (PDEGA), poly(ethylene adipate) (PEA), and poly(butylene succinate) (PBS) with molecular weight from 1247 to 1948 were synthesized through condensation polymerization from adipic acid or butanedioic acid with excess diethylene glycol, ethylene glycol, or butylene glycol. From the HO-terminated polyesters, polyesters with high molecular weight were synthesized by a chain-extending reaction with octamethylcyclotetrasilazane (OMCT) or hexaphenylcyclotrisilazane (HPCT) as chain-extenders. Gel permeation chromatography (GPC) characterization shows that the M_n of chain-extended PDEGA is from 12,644 to 32,870, M_w is from 22,786 to 70,048; M_n of chain-extended PEA is 11,368, M_w is 19,877; and the M_n of chain-extended PBS is from 9823 to 39,873, M_w is from 18,823 to 137,192. The chain-extended polyesters were also characterized by ¹H-NMR spectrum, IR spectra, and DSC spectra. The multiple peaks at 7.37 and 7.67 ppm in the ¹H-NMR spectrum of chain-extended PDEGA and peaks at 3051.1 and 1593.4 cm⁻¹ in the IR spectrum of the chain-extended PBS show the evidence of the  SiPh₂ structure in the polyesters obtained from the chain-extending reaction. DSC study shows that the bulky  SiPh₂ units introduced by the chain-extending reaction lower the regularity of the polyester chains, so the melting point of the chain-extended PBS and PEA decreases compared to that of the original HO-terminated PBS and PEA. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3333–3337, 2004     

Short poly(ethylene glycol) block initiation of poly(l‐lactide) di‐block copolymers: a strategy for tuning the degradation of resorbable devices

The current range of medical applications of resorbable polyesters could be hugely expanded if more effective strategies for tailoring degradation rate were available. Block copolymerisation with poly(ethylene glycol) (PEG) has been shown to reduce degradation times; however, to date, this has relied on the addition of PEG to short lengths of polyester. This results in copolymers with high fractions of PEG and low molecular weights, reducing the potential range of applications. Furthermore, there has been no systematic study of the relative lengths of the blocks. In this work, we employed short hydroxyl‐functionalised methoxy‐terminated mPEG to initiate the synthesis of poly(l ‐lactide) (PLLA), resulting in controlled di‐block copolymers with short mPEG blocks and long PLLA blocks. A controlled series of polymers was made with PLLA lengths (60 < M_n (kg mol^?1) < 200) and mPEG lengths (550 < M_n (g mol^?1) < 5000) giving very low mPEG content (0.1–1.5 wt%). We found that, despite the low fraction of mPEG, water uptake and the rate of hydrolytic degradation, k, increased. Significantly, k for the polymers was dependent only on the presence of mPEG, and was little affected by mPEG length or PLLA length in the ranges studied. Moreover, mass loss began in all polymers when M_n of the polymer fell below a threshold of about 20 kg mol^?1 and depended on both the initial molecular weight of PLLA and the presence (but not the length) of mPEG. Short‐chain mPEG therefore provides a new route for targeted, temporal control of resorbable polyesters for biomedical devices. © 2018 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Synthesis and characterization of biodegradable lactic acid‐based polymers by chain extension

BACKGROUND: Poly(lactic acid) (PLA), coming from renewable resources, can be used to solve environmental problems. However, PLA has to have a relatively high molecular weight in order to have acceptable mechanical properties as required in many applications. Chain‐extension reaction is an effective method to raise the molecular weight of PLA. RESULTS: A high molecular weight biodegradable lactic acid polymer was successfully synthesized in two steps. First, the lactic acid monomer was oligomerized to low molecular weight hydroxyl‐terminated prepolymer; the molecular weight was then increased by chain extension using 1,6‐hexamethylene diisocyanate as the chain extender. The polymer was characterized using ¹H NMR analysis, gel permeation chromatography, differential scanning calorimetry and Fourier transform infrared spectroscopy. The results showed that the obtained polymer had a M_n of 27 500 g mol^?1 and a M_w of 116 900 g mol^?1 after 40 min of chain extension at 180 °C. The glass transition temperature (T_g) of the low molecular weight prepolymer was 47.8 °C. After chain extension, T_g increased to 53.2 °C. The mechanical and rheological properties of the obtained polymer were also investigated. CONCLUSION: The results suggest that high molecular weight PLA can be achieved by chain extension to meet conventional uses. Copyright © 2008 Society of Chemical Industry     

Blocked isocyanates and isocyanated soybean oil as new chain extenders for unsaturated polyesters

Two different blocked isocyanates, diphenylmethane–bis‐4,4′‐ethyleneurea and diphenylmethane–bis‐4,4′‐carbamoil–ϵ‐caprolactam, and isocyanated soybean oil were used as chain extenders for low‐molecular‐weight unsaturated polyesters. Oligomeric polyesters (molecular weight = 600–700), taken from a manufacturing process in the sixth hour of a 16‐h polyesterification reaction, were reacted with these chain extenders, and the desired chain lengths (molecular weight = 1000–1500) were obtained in a very short time through the reaction of the chain extenders with the polyester end groups. The increase in the molecular weight was monitored with gel permeation chromatography. The obtained polymers were characterized with Fourier transform infrared and ¹H‐NMR and with styrene solubility and gel time measurements. After dilution with styrene, the polyesters were cured with a radical initiator. The thermal and mechanical properties of the cured polyesters were examined with dynamic mechanical analysis and thermogravimetric analysis tests and then compared to those of a commercially available reference unsaturated polyester. The results show that unsaturated polyesters can be chain‐extended with these compounds to shorten the polyesterification time substantially without alterations of the styrene solubility or gel time of the polyesters. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis,characterization and biodegradation studies of chain‐coupled polyesters based on tartaric acid

A series of chain‐coupled polyesters based on tartaric acid was synthesized and characterized following a two‐step procedure. In the first step, tartaric acid based hydroxyl terminated polyesters with various alkane diols were prepared and then, in a second step, a chain‐coupling approach using hexamethylene diisocyanate was employed on the synthesized polyesters to prepare a series of chain‐coupled polyesters. The number‐average molecular weights (M_n) of the polyesters were found to vary in the range (4.8 ? 28.1) × 10³ g mol^?1. Thermomechanical studies demonstrate that the storage modulus of the chain‐coupled polyesters decreases with increasing polymethylene chain length which is attributable to enhanced flexibility. The isolation of bacteria on medium containing polymer as the sole source of carbon indicates the ability of the synthesized polyesters to be taken up by microorganisms for growth. © 2013 Society of Chemical Industry     

Preparation and properties of water‐soluble polyester surfactants. III. Preparation and wetting properties of polyethylene glycol–polydimethylsiloxane polyester surfactants

A novel series of water‐soluble polyethylene glycol–polydimethylsiloxane (PEG–Silicone) polyesters was prepared by reacting organopolysiloxane with hydroxyl‐terminated polyester. The polyesters are obtained by the polymerization of maleic anhydride (MA) and PEGs (number‐average molecular weights M _n = 2000–10,000). FTIR, ¹H‐NMR, and elemental analysis were employed to characterized the structures of these compounds. These compounds exhibit good surface activities such as surface tension and low foaming. The influence of the PEG–Silicone polyester surfactants introduced at various concentrations (0.1–2 wt %) was examined by the contact angle method. The measurements performed with various solid substrates indicated that, at comparable concentrations, the PEG–Silicone polyester surfactants were shown to be more efficient for wetting PET and glass. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1236–1241, 2003     

Synthesis and properties of crystalline dicarboxylated poly(L‐lactic acid) prepolymers

Crystalline dicarboxylated poly(L ‐lactic acid)s (dcPLLAs) with number‐average molecular weights (M_n's) of 10³ to 10⁴ g/mol were synthesized via the melt polycondensation of L ‐lactic acid (LLA) in the presence of succinic anhydride (SAD), with tin(II) chloride and toluene‐4‐sulfonic acid as binary catalysts. They were characterized by end‐group titration, ¹H‐NMR, differential scanning calorimetry, and wide‐angle X‐ray diffraction. The terminal COOH percentage reached over 98%, and the molecular weight could be controlled by the molar ratio of LLA to SAD. The thermal behaviors depended on the molecular weight. The poly(L ‐lactic acid)s (PLLAs) crystallized slowly for M_n ≤ 2000 but quickly for M_n ≥ 4000. The crystallinity increased from 27 to 40% when M_n grew from 4000 to 10,000. With comparison to ordinary PLLA, the dcPLLA had the same crystallization structure but a slightly lower crystallizability. The glass‐transition temperature was clearly higher than that of amorphous dcPLLAs. With a controllable molecular weight, high COOH percentage, and crystallinity, the dcPLLA with M_n ≥ 4000 appeared to be a suitable prepolymer for the preparation of high‐molecular‐weight crystalline PLLA via chain extension. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Soft-and hard-segment phase segregation of polyester-based polyurethane

Polyester based polyurethanes were synthesized from 4,4′-methylene bis(phenyl isocyanate) (MDI) with butanediol as a chain extender and low molecular weight polyester-diol as a soft segment. Three polyesters were used in the synthesis of polyurethanes. Two of the polyesters, with molecular weight M_n = 2,660 and 2,155, were synthesized from adipic acid and 1,6-hexanediol, which had an even number of carbon atoms (polyester-6-6-1 and polyester-6-6-2). The other polyester with M_n = 2,770 was synthesized from pimelic acid and 1,5-pentanediol, which had an odd number of carbon atoms (polyester-7-5). Polyester-6-6-1 and polyester-6-6-2 consisting of even carbon monomers, had a higher degree of crystallinity at room temperature than polyester-7-5, which consists of an odd number of carbon monomers. The effect of polyester molecular weight and soft and hard-segmental geometric structure on the soft-and hard-segmental phase segregation was studied using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and small angle X-ray scattering (SAXS).     

Hydrolysis of copolyesters containing aromatic and aliphatic ester blocks by lipase

Copolyesters (CPEs) prepared by the transesterification reaction between aromatic and aliphatic polyesters were hydrolyzed by Rhizopus delemar lipase. The susceptibility of CPEs to hydrolysis by this lipase dropped off rapidly during the initial stage of the transesterification reaction and increased gradually as the reaction proceeded. The susceptibility to hydrolysis decreased with increase in aromatic polyester content. It was concluded that the rigidity of the aromatic ring in the CPE chains strongly influenced their susceptibility to hydrolysis by this lipase.     

Block copolymer synthesis and chain extension from TEMPO‐terminated chains formed by ultrasonic chain scission

Long poly(ethyl methacrylate) (M_n = 2,300,000) and polystyrene (M_n = 1,200,000) chains were subjected to ultrasonic scission in the presence of a radical scavenger, 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO). This procedure yielded polymers with lower molecular weights and TEMPO terminal units. Application of these polymers in stable radical mediated polymerization of styrene resulted in chain extension and block copolymers, depending on the precursor polymer. Block copolymer formation was evidenced by NMR measurement, and chain extension was shown by GPC analysis. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1950–1953, 2000     

Atom transfer radical polymerization grafting of highly functionalized polystyrene and poly(4‐methylstyrene) macroinitiators with tert‐butyl acrylate

Two monodisperse graft copolymers, poly(4‐methylstyrene)‐graft‐poly(tert‐butyl acrylate) [number‐average molecular weight (M_n) = 37,500, weight‐average molecular weight/number‐average molecular weight (M_w/M_n) = 1.12] and polystyrene‐graft‐poly(tert‐butyl acrylate) (M_n = 72,800, M_w/M_n = 1.12), were prepared by the atom transfer radical polymerization of tert‐butyl acrylate catalyzed with Cu(I) halides. As macroinitiators, poly{(4‐methylstyrene)‐co‐[(4‐bromomethyl)styrene]} and poly{styrene‐co‐[4‐(1‐(2‐bromopropionyloxy)ethyl)styrene]}, carrying 40% of the bromoalkyl functionalities along the chain, were used. The dependencies of molecular parameters on monomer conversion fulfilled the criteria for controlled polymerizations. In contrast, the dependencies of monomer conversion versus time were nonideal; possible causes were examined. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2930–2936, 2002     

Synthesis of polysiloxane–polyester copolymer by lipase‐catalyzed polycondensation

Polysiloxane–polyester copolymers have been synthesized for the first time by direct polycondensation of a series of diacids (butanedioic, hexanedioic, and octanedioic acid) and α,ω‐bis(3‐hydroxypropyl) polydimethylsiloxanes catalyzed with Novozyme‐435 in high yields (>90%) without the cleavage of Si? O bonds. The effects of monomer chain length, reaction temperature, and water removal method on the number–average molecular weight (M_n) of the resulted copolymers were investigated. Thermogravimetric and differential scanning calorimetry analyses indicated that the produced copolymer was more thermally stable than poly(1,8‐octyladipate) and the T_g was lowered to ?111°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008