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1.
Tomoko Fujiwara Yoshiharu Kimura Iwao Teraoka 《Journal of polymer science. Part A, Polymer chemistry》2000,38(13):2405-2414
An AB diblock copolymer of poly(L ‐lactide) (PLLA) and poly(oxyethylene) (PEG) with a cinnamate terminal in the PEG block was prepared by the copolymerization of L ‐lactide and partially end‐modified PEG followed by fractionation. The first step was the terminal modification of PEG with cinnamoyl chloride (CC), in which the degree of cinnamoylation of the hydroxyl terminals of PEG was roughly controlled by the feed ratio of both reactants. The resultant PEG cinnamate was subjected to copolymerization with L ‐lactide to produce a mixture of unreacted PEG dicinnamate (C‐PEG‐C), the diblock copolymer (PLLA‐PEG‐C), and the triblock copolymer (PLLA‐PEG‐PLLA) corresponding to the three components of the PEG cinnamate. This mixture was separated by phase fluctuation chromatography (PFC) to obtain PLLA‐PEG‐C in sufficient purity. This process, involving the stoichiometric control of the terminal reaction of telechelic oligomers and the utilization of PFC for fractionation, can be an efficient method for synthesizing end‐functionalized diblock copolymers from readily available telechelic oligomers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2405–2414, 2000 相似文献
2.
Chang‐Ming Dong Kun‐Yuan Qiu Zhong‐Wei Gu Xin‐De Feng 《Journal of polymer science. Part A, Polymer chemistry》2002,40(3):409-415
Two types of three‐arm and four‐arm, star‐shaped poly(D,L ‐lactic acid‐alt‐glycolic acid)‐b‐poly(L ‐lactic acid) (D,L ‐PLGA50‐b‐PLLA) were successfully synthesized via the sequential ring‐opening polymerization of D,L ‐3‐methylglycolide (MG) and L ‐lactide (L ‐LA) with a multifunctional initiator, such as trimethylolpropane and pentaerythritol, and stannous octoate (SnOct2) as a catalyst. Star‐shaped, hydroxy‐terminated poly(D,L ‐lactic acid‐alt‐glycolic acid) (D,L ‐PLGA50) obtained from the polymerization of MG was used as a macroinitiator to initiate the block polymerization of L ‐LA with the SnOct2 catalyst in bulk at 130 °C. For the polymerization of L ‐LA with the three‐arm, star‐shaped D,L ‐PLGA50 macroinitiator (number‐average molecular weight = 6800) and the SnOct2 catalyst, the molecular weight of the resulting D,L ‐PLGA50‐b‐PLLA polymer linearly increased from 12,600 to 27,400 with the increasing molar ratio (1:1 to 3:1) of L ‐LA to MG, and the molecular weight distribution was rather narrow (weight‐average molecular weight/number‐average molecular weight = 1.09–1.15). The 1H NMR spectrum of the D,L ‐PLGA50‐b‐PLLA block copolymer showed that the molecular weight and unit composition of the block copolymer were controlled by the molar ratio of L ‐LA to the macroinitiator. The 13C NMR spectrum of the block copolymer clearly showed its diblock structures, that is, D,L ‐PLGA50 as the first block and poly(L ‐lactic acid) as the second block. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 409–415, 2002 相似文献
3.
Chen Cai Lu Wang Chang‐Ming Dong 《Journal of polymer science. Part A, Polymer chemistry》2006,44(6):2034-2044
Well‐defined poly(L ‐lactide)‐b‐poly(ethylene oxide) (PLLA‐b‐PEO) copolymers with different branch arms were synthesized via the controlled ring‐opening polymerization of L ‐lactide followed by a coupling reaction with carboxyl‐terminated poly(ethylene oxide) (PEO); these copolymers included both star‐shaped copolymers having four arms (4sPLLA‐b‐PEO) and six arms (6sPLLA‐b‐PEO) and linear analogues having one arm (LPLLA‐b‐PEO) and two arms (2LPLLA‐b‐PEO). The maximal melting point, cold‐crystallization temperature, and degree of crystallinity (Xc) of the poly(L ‐lactide) (PLLA) block within PLLA‐b‐PEO decreased as the branch arm number increased, whereas Xc of the PEO block within the copolymers inversely increased. This was mainly attributed to the relatively decreasing arm length ratio of PLLA to PEO, which resulted in various PLLA crystallization effects restricting the PEO block. These results indicated that both the PLLA and PEO blocks within the block copolymers mutually influenced each other, and the crystallization of both the PLLA and PEO blocks within the PLLA‐b‐PEO copolymers could be adjusted through both the branch arm number and the arm length of each block. Moreover, the spherulitic growth rate (G) decreased as the branch arm number increased: G6sPLLA‐b‐PEO < G4sPLLA‐b‐PEO < G2LPLLA‐b‐PEO < GLPLLA‐b‐PEO. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2034–2044, 2006 相似文献
4.
Junliang Yang Ting Zhao Jijun Cui Leijing Liu Yunchun Zhou Gao Li Enle Zhou Xuesi Chen 《Journal of Polymer Science.Polymer Physics》2006,44(22):3215-3226
The confined crystallization behavior, melting behavior, and nonisothermal crystallization kinetics of the poly(ethylene glycol) block (PEG) in poly(L ‐lactide)–poly(ethylene glycol) (PLLA–PEG) diblock copolymers were investigated with wide‐angle X‐ray diffraction and differential scanning calorimetry. The analysis showed that the nonisothermal crystallization behavior changed from fitting the Ozawa equation and the Avrami equation modified by Jeziorny to deviating from them with the molecular weight of the poly(L ‐lactide) (PLLA) block increasing. This resulted from the gradual strengthening of the confined effect, which was imposed by the crystallization of the PLLA block. The nucleation mechanism of the PEG block of PLLA15000–PEG5000 at a larger degree of supercooling was different from that of PLLA2500–PEG5000, PLLA5000–PEG5000, and PEG5000 (the numbers after PEG and PLLA denote the molecular weights of the PEG and PLLA blocks, respectively). They were homogeneous nucleation and heterogeneous nucleation, respectively. The PLLA block bonded chemically with the PEG block and increased the crystallization activation energy, but it provided nucleating sites for the crystallization of the PEG block, and the crystallization rate rose when it was heterogeneous nucleation. The number of melting peaks was three and one for the PEG homopolymer and the PEG block of the diblock copolymers, respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3215–3226, 2006 相似文献
5.
Jun Shao Zhaohui Tang Jingru Sun Gao Li Xuesi Chen 《Journal of Polymer Science.Polymer Physics》2014,52(23):1560-1567
Linear and four‐armed poly(l ‐lactide)‐block‐poly(d ‐lactide) (PLLA‐b‐PDLA) block copolymers are synthesized by ring‐opening polymerization of d ‐lactide on the end hydroxyl of linear and four‐armed PLLA prepolymers. DSC results indicate that the melting temperature and melting enthalpies of poly (lactide) stereocomplex in the copolymers are obviously lower than corresponding linear and four‐armed PLLA/PDLA blends. Compared with the four‐armed PLLA‐b‐PDLA copolymer, the similar linear PLLA‐b‐PDLA shows higher melting temperature (212.3 °C) and larger melting enthalpy (70.6 J g?1). After these copolymers blend with additional neat PLAs, DSC, and WAXD results show that the stereocomplex formation between free PLA molecular chain and enantiomeric PLA block is the major stereocomplex formation. In the linear copolymer/linear PLA blends, the stereocomplex crystallites (sc) as well as homochiral crystallites (hc) form in the copolymer/PLA cast films. However, in the four‐armed copolymer/linear PLA blends, both sc and hc develop in the four‐armed PLLA‐b‐PDLA/PDLA specimen, which means that the stereocomplexation mainly forms between free PDLA molecule and the inside PLLA block, and the outside PDLA block could form some microcrystallites. Although the melting enthalpies of stereocomplexes in the blends are smaller than that of neat copolymers, only two‐thirds of the molecular chains participate in the stereocomplex formation, and the crystallization efficiency strengthens. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1560–1567 相似文献
6.
Jamie M. Messman Robson F. Storey 《Journal of polymer science. Part A, Polymer chemistry》2006,44(23):6817-6835
Ethylene glycol (EG) initiated, hydroxyl‐telechelic poly(L ‐lactide) (PLLA) was employed as a macroinitiator in the presence of a stannous octoate catalyst in the ring‐opening polymerization of 5‐methyl‐5‐benzyloxycarbonyl‐1,3‐dioxan‐2‐one (MBC) with the goal of creating A–B–A‐type block copolymers having polycarbonate outer blocks and a polyester center block. Because of transesterification reactions involving the PLLA block, multiblock copolymers of the A–(B–A)n–B–A type were actually obtained, where A is poly(5‐methyl‐5‐benzyloxycarbonyl‐1,3‐dioxan‐2‐one), B is PLLA, and n is greater than 0. 1H and 13C NMR spectroscopy of the product copolymers yielded evidence of the multiblock structure and provided the lactide sequence length. For a PLLA macroinitiator with a number‐average molecular weight of 2500 g/mol, the product block copolymer had an n value of 0.8 and an average lactide sequence length (consecutive C6H8O4 units uninterrupted by either an EG or MBC unit) of 6.1. For a PLLA macroinitiator with a number‐average molecular weight of 14,400 g/mol, n was 18, and the average lactide sequence length was 5.0. Additional evidence of the block copolymer architecture was revealed through the retention of PLLA crystallinity as measured by differential scanning calorimetry and wide‐angle X‐ray diffraction. Multiblock copolymers with PLLA crystallinity could be achieved only with isolated PLLA macroinitiators; sequential addition of MBC to high‐conversion L ‐lactide polymerizations resulted in excessive randomization, presumably because of residual L ‐lactide monomer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6817–6835, 2006 相似文献
7.
Moon Suk Kim Kwang Su Seo Gilson Khang Sun Hang Cho Hai Bang Lee 《Journal of polymer science. Part A, Polymer chemistry》2004,42(22):5784-5793
Diblock copolymers consisting of methoxy poly(ethylene glycol) (MPEG) and poly(?‐caprolactone) (PCL), poly(δ‐valerolactone) (PVL), poly(L ‐lactic acid) (PLLA), or poly(lactic‐co‐glycolic acid) (PLGA) as biodegradable polyesters were prepared to examine the phase transition of diblock copolymer solutions. MPEG–PCL and MPEG–PVL diblock copolymers and MPEG–PLLA and MPEG–PLGA diblock copolymers were synthesized by the ring‐opening polymerization of ?‐caprolactone or δ‐valerolactone in the presence of HCl · Et2O as a monomer activator at room temperature and by the ring‐opening polymerization of L ‐lactide or a mixture of L ‐lactide and glycolide in the presence of stannous octoate at 130 °C, respectively. The synthesized diblock copolymers were characterized with 1H NMR, IR, and gel permeation chromatography. The phase transitions for diblock copolymer aqueous solutions of various concentrations were explored according to the temperature variation. The diblock copolymer solutions exhibited the phase transition from gel to sol with increasing temperature. As the polyester block length of the diblock copolymers increased, the gel‐to‐sol transition moved to a lower concentration region. The gel‐to‐sol transition showed a dependence on the length of the polyester block segment. According to X‐ray diffraction and differential scanning calorimetry thermal studies, the gel‐to‐sol transition of the diblock copolymer solutions depended on their degrees of crystallinity because water could easily diffuse into amorphous polymers in comparison with polymers with a crystalline structure. The crystallinity markedly depended on both the distinct character and composition of the block segment. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5784–5793, 2004 相似文献
8.
Ching‐I Huang Shang‐Hsiu Tsai Chih‐Ming Chen 《Journal of Polymer Science.Polymer Physics》2006,44(17):2438-2448
The crystal unit‐cell structures and the isothermal crystallization kinetics of poly(L ‐lactide) in biodegradable poly(L ‐lactide)‐block‐methoxy poly(ethylene glycol) (PLLA‐b‐MePEG) diblock copolymers have been analyzed by wide‐angle X‐ray diffraction and differential scanning calorimetry. In particular, the effects due to the presence of MePEG that is chemically connected to PLLA as well as the PLLA crystallization temperature TC are examined. Though we observe no variation of both the PLLA and MePEG crystal unit‐cell structures with the block ratio between PLLA and MePEG and TC, the isothermal crystallization kinetics of PLLA is greatly influenced by the presence of MePEG that is connected to it. In particular, the equilibrium melting temperature of PLLA, T, significantly decreases in the diblock copolymers. When the TC is high so that the crystallization is controlled by nucleation, because of the decreasing T and thereafter the nucleation density with decreasing PLLA molecular weight, the crystallinity of PLLA also decreases with a decrease in the PLLA molecular weight. While, for the lower crystallization temperature regime controlled by the growth mechanism, the crystallizability of PLLA in copolymers is greater than that of pure PLLA. This suggests that the activation energy for the PLLA segment diffusing to the crystallization site decreases in the diblocks. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2438–2448, 2006 相似文献
9.
Wen‐Da Li Jian‐Bing Zeng Yi‐Dong Li Xiu‐Li Wang Yu‐Zhong Wang 《Journal of polymer science. Part A, Polymer chemistry》2009,47(21):5898-5907
A series of aliphatic–aromatic multiblock copolyesters consisting of poly(ethylene‐co‐1,6‐hexene terephthalate) (PEHT) and poly(L ‐lactic acid) (PLLA) were synthesized successfully by chain‐extension reaction of dihydroxyl terminated PEHT‐OH prepolymer and dihydroxyl terminated PLLA‐OH prepolymer using toluene‐2,4‐diisoyanate as a chain extender. PEHT‐OH prepolymers were prepared by two step reactions using dimethyl terephthalate, ethylene glycol, and 1,6‐hexanediol as raw materials. PLLA‐OH prepolymers were prepared by direct polycondensation of L ‐lactic acid in the presence of 1,4‐butanediol. The chemical structures, the molecular weights and the thermal properties of PEHT‐OH, PLLA‐OH prepolymers, and PEHT‐PLLA copolymers were characterized by FTIR, 1H NMR, GPC, TG, and DSC. This synthetic method has been proved to be very efficient for the synthesis of high‐molecular‐weight copolyesters (say, higher than Mw = 3 × 105 g/mol). Only one glass transition temperature was found in the DSC curves of PEHT‐PLLA copolymers, indicating that the PLLA and PEHT segments had good miscibility. TG curves showed that all the copolyesters had good thermal stabilities. The resulting novel aromatic–aliphatic copolyesters are expected to find a potential application in the area of biodegradable polymer materials. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5898–5907, 2009 相似文献
10.
Gisha Elizabeth Luckachan C. K. S. Pillai 《Journal of polymer science. Part A, Polymer chemistry》2006,44(10):3250-3260
Novel multiblock poly(ester amide)s containing poly(L ‐lactide) and cycloaliphatic amide segments were synthesized from telechelic oligomer of α,ω‐hydroxyl terminated poly(L ‐lactide), 1,3‐cyclohexylbis(methylamine), and sebacoylchloride by the “two‐step” interfacial polycondensation method. The blocky nature of PEAs was established by FTIR and 1H NMR spectroscopies. The effect of relative content of ester and amide segments on the crystallization nature of PEAs was investigated by WAXD and DSC analyses. PEAs having lower content of PLLA, PEA 1 and PEA 2, showed a crystallization pattern analogous to polyamides, whereas PEA 3, having higher content of PLLA, showed two crystalline phases characterized by polyester and polyamide segments. Random nature of PEAs was observed from single Tg values. Biodegradation studies using the enzyme lipase from Candida Cylindracea showed higher degradation rate for PEA 3 than that for PEA 1 and PEA 2. FTIR, 1H NMR, and DSC analyses of the degraded products indicated the involvement of ester linkages in the degradation process. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3250–3260, 2006 相似文献
11.
Ulrica Edlund Ann‐Christine Albertsson 《Journal of polymer science. Part A, Polymer chemistry》2000,38(5):786-796
Morphology is presented as a powerful tool to control the in vitro degradation and drug release characteristics of novel drug delivery microspheres prepared from homopolymer blends of 1,5‐dioxepan‐2‐one, DXO, and L ‐lactide, L‐LA. Their performance in this respect was compared to analogous P(L‐LA‐co‐DXO) microspheres. Blends formed denser and less porous microspheres with a higher degree of matrix crystallinity than copolymers of corresponding L‐LA:DXO composition. The morphology differences of blends and copolymers, further adjustable by means of component ratio, are shown to have a vital impact on the in vitro performance. Sustained drug delivery was obtained from both copolymers and blends. Molecular weight loss was retarded and diffusion‐mediated release was inhibited in the latter case, further delaying the release process. The effects of storage on the physicochemical properties of these systems were evaluated under desiccated and moist conditions for 5 months. Storage‐induced physicochemical changes, such as matrix crystallization and molecular weight decrease, were accelerated at higher relative humidities. P(L‐LA‐co‐DXO) demonstrated higher moisture sensitivity than a PLLA‐PDXO blend of corresponding composition. The more crystalline and dense morphology of blend microspheres may thus be considered an improvement of the storage stability. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 786–796, 2000 相似文献
12.
Fanglian Yao Yun Bai Yutao Zhou Chang Liu Hao Wang Kangde Yao 《Journal of polymer science. Part A, Polymer chemistry》2003,41(13):2073-2081
Because poly(L ‐lactic acid) (PLLA) is a biodegradable polyester with low immunogenicity and good biocompatibility, it is used as a biomaterial. However, hydrophobic PLLA does not have any reactive groups. Thus, its application is limited. To increase the hydrophilicity of PLLA and accelerate its degradation rate, functionalized pendant groups and blocks were introduced through copolymerization with citric acid and poly(ethylene glycol) (PEG), respectively. This article describes the synthesis and characterization of poly(L ‐lactic‐co‐citric acid) (PLCA)‐PLLA and PLCA‐PEG multiblock copolymers. The results indicated that the hydrolysis rate was enhanced, and the hydrophilicity was improved because of the incorporation of carboxyl groups in PLCA‐PLLA. The joining of the PEG block led to improved hydrophilicity of PLCA, and the degradation rate of PLCA‐PEG accelerated as compared with that of PLCA‐PLLA. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2073–2081, 2003 相似文献
13.
Julien Ramier Estelle Renard Daniel Grande 《Journal of polymer science. Part A, Polymer chemistry》2012,50(7):1445-1455
Microwave (MW)‐assisted ring‐opening polymerization (ROP) provides a rapid and straightforward method for engineering a wide array of well‐defined poly(3‐hydroxyalkanoate)‐b‐poly(D,L ‐lactide) (PHA‐b‐PLA) diblock copolymers. On MW irradiation, the bulk ROP of D,L ‐lactide (LA) could be efficiently triggered by a series of monohydroxylated PHA‐based macroinitiators previously produced via acid‐catalyzed methanolysis of corresponding native PHAs, thus affording diblock copolyesters with tunable compositions. The dependence of LA polymerization on temperature, macroinitiator structure, irradiation time, and [LA]0/[PHA]0 molar ratio was carefully investigated. It turned out that initiator efficiency values close to 1 associated with conversions ranging from 50 to 85% were obtained only after 5 min at 115 °C. A kinetic investigation of the MW‐assisted ROP of LA gave evidence of its “living”/controlled character under the experimental conditions selected. Structural analyses and thermal properties of biodegradable diblock copolyesters were also performed. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
14.
Umaprasana Ojha Pallavi Kulkarni Jagdeep Singh Rudolf Faust 《Journal of polymer science. Part A, Polymer chemistry》2009,47(14):3490-3505
The syntheses of {‐poly(L ‐lactide) (PLLA)‐b‐polyisobutylene (PIB)‐}n multiblock copolymers were accomplished for the first time by chain extension of PLLA‐b‐PIB‐b‐PLLA triblock copolymers. Well‐defined PLLA‐b‐PIB‐b‐PLLA triblock copolymers with predictable Mns, low PDIs (1.10–1.18) and excellent blocking efficiencies were prepared by anionic ring‐opening polymerizations of L ‐lactide initiated with hydroxyallyl telechelic PIB (HO‐Allyl‐PIB‐Allyl‐OH) in toluene at 110 °C. The triblock copolymers were successfully chain extended with 4,4′‐methylenebis(phenylisocyanate) (MDI) to obtain the multiblock copolymers with good gravimetric yields of ~86 to 96%. The chain‐extended polymers were soluble in a range of common organic solvents. The block copolymers showed two glass transition temperatures in differential scanning calorimetric analysis for the PIB and PLLA blocks indicating microphase separation, which was supported by atomic force microscopy images. The as‐synthesized compression molded multiblock copolymers exhibited tensile strengths in the range of 8–24 MPa with elongations at break in the range of 2.5–400%. The static and dynamic mechanical properties showed a strong dependence on the relative PLLA content in the copolymer. The dynamic mechanical analysis also indicated microphase separation at higher PLLA compositions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3490–3505, 2009 相似文献
15.
Hiroyuki Shirahama Kiyoshi Mizuma Koichi Umemoto Hajime Yasuda 《Journal of polymer science. Part A, Polymer chemistry》2001,39(9):1374-1381
Homopoly(L ‐lactide) and homopoly(D,L ‐lactide) were almost inert for biodegradation with tricine buffer or normal enzymes such as bromelain, pronase, and cholesterol esterase but biodegradable with proteinase K. Significantly enhanced biodegradation was observed when an optically active (R)‐ or (S)‐3‐methyl‐4‐oxa‐6‐hexanolide (MOHEL) unit was introduced into poly(L ‐lactide) [poly(L ‐LA)] or poly(D,L ‐lactide) [poly(D,L ‐LA)] sequences. Poly[L ‐LA‐ran‐(R)‐MOHEL] in molar ratios of 86/14 to 43/57 showed good biodegradability that was independent of crystallinity. The biodegradation of polymers with proteinase K increased in the following order: poly[D,L ‐LA‐ran‐(R)‐MOHEL] > poly[L ‐LA‐ran‐(R)‐MOHEL] > poly[D,L ‐LA‐ran‐(S)‐MOHEL] > poly[L ‐LA‐ran‐(S)‐MOHEL] > poly(R)‐MOHEL > poly(D,L ‐LA). The number‐average molecular weight, molecular weight distribution, glass‐transition temperature, and melting temperature did not change before and after the biodegradation of poly[L ‐LA‐ran‐(R)‐MOHEL], indicating that the degradation occurred from the polymer surface. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1374–1381, 2001 相似文献
16.
Hideko T. Oyama Yoshikazu Tanaka Sakiko Hirai Shigenari Shida Ayako Kadosaka 《Journal of Polymer Science.Polymer Physics》2011,49(5):342-354
In this study, novel biodegradable materials were successfully generated, which have excellent mechanical properties in air during usage and storage, but whose structure easily disintegrates when immersed in water. The materials were prepared by melt blending poly(L ‐lactic acid) (PLLA) and poly(butylene adipate‐co‐terephthalate) (PBAT) with a small amount of oligomeric poly(aspartic acid‐co‐lactide) (PAL) as a degradation accelerator. The degradation behavior of the blends was investigated by immersing the blend films in phosphate‐buffered saline (pH = 7.3) at 40 °C. It was shown that the PAL content and composition significantly affected morphology, mechanical properties, and hydrolysis rate of the blends. It was observed that the blends containing PAL with higher molar ratios of L ‐lactyl [LA]/[Asp] had smaller PBAT domain size, showing better mechanical properties when compared with those containing PAL with lower molar ratios of [LA]/[Asp]. The degradation rates of both PLLA and PBAT components in the ternary blends simultaneously became higher for the blends containing PAL with higher molar ratios of [LA]/[Asp]. It was confirmed that the PLLA component and its decomposed materials efficiently catalyze the hydrolytic degradation of the PBAT component, but by contrast that the PBAT component and its decomposed materials do not catalyze the hydrolytic degradation of the PLLA component in the blends. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010 相似文献
17.
Yahia Lemmouchi Michael C. Perry Allan J. Amass Khirud Chakraborty Etienne Schacht 《Journal of polymer science. Part A, Polymer chemistry》2007,45(17):3966-3974
Biodegradable star‐shaped poly(ethylene glycol)‐block‐poly(lactide) copolymers were synthesized by ring‐opening polymerization of lactide, using star poly(ethylene glycol) as an initiator and potassium hexamethyldisilazide as a catalyst. Polymerizations were carried out in toluene at room temperature. Two series of three‐ and four‐armed PEG‐PLA copolymers were synthesized and characterized by gel permeation chromatography (GPC) as well as 1H and 13C NMR spectroscopy. The polymerization under the used conditions is very fast, yielding copolymers of controlled molecular weight and tailored molecular architecture. The chemical structure of the copolymers investigated by 1H and 13C NMR indicates the formation of block copolymers. The monomodal profile of molecular weight distribution by GPC provided further evidence of controlled and defined star‐shaped copolymers as well as the absence of cyclic oligomeric species. The effects of copolymer composition and lactide stereochemistry on the physical properties were investigated by GPC and differential scanning calorimetry. For the same PLA chain length, the materials obtained in the case of linear copolymers are more viscous, whereas in the case of star copolymer, solid materials are obtained with reduction in their Tg and Tm temperatures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3966–3974, 2007 相似文献
18.
Sungil Moon Masatoshi Iji 《Journal of polymer science. Part A, Polymer chemistry》2008,46(13):4433-4441
A new poly(butylene succinate) (PBS)‐grafted vapor grown carbon fiber (VGCF)/poly(L ‐lactide) (PLLA) nanocomposites were successfully prepared by an in situ condensation reaction between PBS (Mw = 6,000) and surface oxidized VGCF, followed by direct melt mixing technique, and their mechanical and thermal properties were evaluated. Fourier transform infrared spectroscopy and scanning electron microscopy studies indicate a chemical interaction between the PBS and the surface of VGCF. It was found that the maximum tensile strength and modulus of PBS‐grafted VGCF/PLLA nanocomposites were 135 MPa (27% increase relative to neat PLLA) and 4,400 MPa (29% increase relative to neat PLLA), respectively. The results indicate that significant improvement in the mechanical properties can be accomplished by optimizing the surface modification conditions for VGCF. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4433–4441, 2008 相似文献
19.
Thermoplastic elastomers based on poly(l‐Lysine)‐Poly(ε‐Caprolactone) multi‐block copolymers 下载免费PDF全文
Jun Ling Xiaoqing Wang Lixin You Zhiquan Shen 《Journal of polymer science. Part A, Polymer chemistry》2016,54(18):3012-3018
Novel thermoplastic elastomers based on multi‐block copolymers of poly(l ‐lysine) (PLL), poly(N‐ε‐carbobenzyloxyl‐l ‐lysine) (PZLL), poly(ε‐caprolactone) (PCL), and poly(ethylene glycol) (PEG) were synthesized by combination of ring‐opening polymerization (ROP) and chain extension via l ‐lysine diisocyanate (LDI). SEC and 1H NMR were used to characterize the multi‐block copolymers, with number‐average molecular weights between 38,900 and 73,400 g/mol. Multi‐block copolymers were proved to be good thermoplastic elastomers with Young's modulus between 5 and 60 MPa and tensile strain up to 1300%. The PLL‐containing multi‐block copolymers were electrospun into non‐woven mats that exhibited high surface hydrophilicity and wettability. The polypeptide–polyester materials were biocompatible, bio‐based and environment‐friendly for promising wide applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3012–3018 相似文献
20.
Hui‐Li Guan Zhi‐Gang Xie Pei‐Biao Zhang Xin Wang Xue‐Si Chen Xian‐Hong Wang Xia‐Bin Jing 《Journal of polymer science. Part A, Polymer chemistry》2005,43(20):4771-4780
An amphiphilic block copolymer, poly(ethylene glycol)‐block‐poly(L ‐lactide‐co‐2‐methyl‐2‐benzoxycarbonyl‐propylene carbonate) [PEG‐b‐P(LA‐co‐MBC)], was synthesized in bulk by the ring‐opening polymerization of L ‐lactide with 2‐methyl‐2‐benzoxycarbonyl‐propylene carbonate (MBC) in the presence of poly(ethylene glycol) as a macroinitiator with diethyl zinc as a catalyst. The subsequent catalytic hydrogenation of PEG‐b‐P(LA‐co‐MBC) with palladium hydroxide on activated charcoal (20%) as a catalyst was carried out to obtain the corresponding linear copolymer poly(ethyleneglycol)‐block‐poly(L ‐lactide‐co‐2‐methyl‐2‐carboxyl‐propylenecarbonate) [PEG‐b‐P(LA‐co‐MCC)] with pendant carboxyl groups. DSC analysis indicated that the glass‐transition temperature (Tg) of PEG‐b‐P(LA‐co‐MBC) decreased with increasing MBC content in the copolymer, and Tg of PEG‐b‐P(LA‐co‐MCC) was higher than that of the corresponding PEG‐b‐P(LA‐co‐MBC). The in vitro degradation rate of PEG‐b‐P(LA‐co‐MCC) in the presence of proteinase K was faster than that of PEG‐b‐P(LA‐co‐MBC), and the cytotoxicity of PEG‐b‐P(LA‐co‐MCC) to chondrocytes from human fetal arthrosis was lower than that of poly(L ‐lactide). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4771–4780, 2005 相似文献