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1.
Toshifumi Satoh Masaki Tamaki Yoshikazu Kitajyo Takahiro Maeda Hiroyuki Ishihara Tomoko Imai Harumi Kaga Toyoji Kakuchi 《Journal of polymer science. Part A, Polymer chemistry》2006,44(1):406-413
A novel biodegradable unimolecular reversed micelle consisting of a poly(L ‐lactide) (PLA) shell and a hyperbranched D ‐mannan (HBM) core, that is, a chestnut‐shaped polymer (PLA–HBM), was synthesized by the polymerization of L ‐lactide on HBM with 4‐(dimethylamino)pyridine (DMAP) as the catalyst. The obtained polymers were soluble in dimethyl sulfoxide, tetrahydrofuran, and chloroform but insoluble in H2O. The molecular weights of the PLA chain on PLA–HBM tended to increase with increasing polymerization time. The number of PLA chains on PLA–HBM could be controlled by the ratio of DMAP to the sugar unit in HBM. The obtained copolymer, PLA–HBM, acted as a unimolecular reversed micelle with an encapsulation ability toward the hydrophilic molecule. In addition, the entrapped hydrophilic molecules were slowly released from the core of PLA–HBM, and the release rate was accelerated by the breaking of the PLA chains of the shell when proteinase K as a hydrolase of PLA was used. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 406–413, 2006 相似文献
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Synthesis,characterization, and thermal stability of poly (lactic acid)/zinc oxide pillared organic saponite nanocomposites via ring‐opening polymerization of d,l‐lactide 下载免费PDF全文
Poly (lactic acid) (PLA) was synthesized using d , l ‐lactide monomer and zinc oxide (ZnO) pillared organic saponite as the green catalyst, through ring‐opening polymerization. The effects of stoichiometry of catalyst and polymerization conditions on molecular weight of PLA were evaluated by orthogonal experiment. The optimum polymerization parameters were: 0.5 wt% ZnO pillared organic saponite and reaction conditions of 170°C for 20 hr. Fourier transform infrared spectroscopy and 1H nuclear magnetic resonance spectroscopy confirmed the PLA structure. Gel permeation chromatography showed that the average molecular weight of PLA was 48,442 g/mol, and its polydispersity index was 1.875. Differential scanning calorimetry, X‐ray diffraction, and polarized optical microscopy showed that ZnO pillared organic saponite improved the crystallinity of PLA. Thermal gravimetric analysis showed improved thermal stability of PLA because of ZnO pillared organic saponite. Thermal decomposition kinetics of PLA/ZnO pillared organic saponite nanocomposites was also studied. The activation energies (Ea) for thermal degradation of PLA and PLA/ZnO pillared organic saponite nanocomposites were evaluated by the Kissinger and Ozawa methods, which demonstrated that ZnO pillared organic saponite enhanced Ea of thermal degradation of PLA and significantly improved its thermal stability. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
3.
Małgorzata Baśko Przemysław Kubisa 《Journal of polymer science. Part A, Polymer chemistry》2010,48(12):2650-2658
Cationic bulk polymerization of L ,L‐ lactide (LA) initiated by trifluromethanesulfonic acid [triflic acid (TfA)] has been studied. At temperatures 120–160 °C, polymerization proceeded to high conversion (>90% within ~8 h) giving polymers with Mn ~ 2 × 104 and relatively high dispersity. Thermogravimetric analysis of resulting polylactide (PLA) indicated that its thermal stability was considerably higher than the thermal stability of linear PLA of comparable molecular weight obtained with ROH/Sn(Oct)2 initiating system. Also hydrolytic stability of cationically prepared PLA was significantly higher than hydrolytic stability of linear PLA. Because thermal or hydrolytic degradation of PLA starting from end‐groups is considerably faster than random chain scission, both thermal and hydrolytic stability depend on molecular weight of the polymer. High thermal and hydrolytic stability, in spite of moderate molecular weight of cationically prepared PLA, indicate that the fraction of end‐groups is considerably lower than in linear PLA of comparable molecular weight. According to proposed mechanism of cationic LA polymerization growing macromolecules are fitted with terminal ? OH and ? C(O)OSO2CF3 end‐groups. The presence of those groups allows efficient end‐to‐end cyclization. Cyclic nature of resulting PLA explains its higher thermal and hydrolytic stability as compared with linear PLA. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2650–2658, 2010 相似文献
4.
(D, L)-Lactide (LA) was first polymerized with one component of rare earth cata-lysts [Nd(naph)_3, Nd(oct)_3, Nd(O-iPr)3, Nd(AcAc)_3, Y(AcAc)_3, Sm(AcAc)_3, Er(AcAc)_3)]respectively in solution and in melt state. The effects of [Cat]/[LA] molar ratio, solvents,polymerization time, temperature, various rare earth elements and ligands were investi-gated in detail. The results showed that both the conversion of polymerization and themolecular weight (MW) of poly (D, L-Lactide) (PLA) in melt polymerization are higherthan that in solution polymerization, but the polymerization rate in melt was lowr than insolution. The molecular weight distribution (MWD) of PLA is broader with increasing tem-perature. X-ray study indicated that PLA obtained by Nd(AcAc)_3 in melt polymerizationis an amorphous polymer. 相似文献
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Pouneh S. Pourhosseini Reza Amani Ali A. Saboury Farhood Najafi Mohammad Imani 《Journal of the Iranian Chemical Society》2014,11(2):467-470
A series of poly(l-lactic acid)/poly(ethylene glycol) triblock copolymers with a PLA–PEG–PLA architecture were synthesized by a ring-opening polymerization (ROP) process. The copolymers were characterized by 1H NMR and GPC. The total number average molecular weights were in the range of 4,700–50,000, whereas the degrees of polymerization of the PLA and PEG blocks varied from 15 to 359 and from 68 to 136, respectively. The self-association of these copolymers in aqueous environment was studied by emission fluorescence spectroscopy of anilinonaphthalene probe and the critical association concentration (CAC) of the copolymers was measured. It was found that the micellization process of these copolymers was mainly determined by the length of the hydrophobic LA block, while the length of the hydrophilic PEG block had little effect. Furthermore, the low CAC values of the copolymers suggest that the copolymers form stable supramolecular structures in aqueous solutions. 相似文献
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Dina A.S. Marques Susana Jarmelo Cristina M.S. G. Baptista M.H. Gil 《Macromolecular Symposia》2010,296(1):63-71
The step-growth polymerization of L-lactic acid in solution was studied in this work. In order to attain a polymer with high molecular weight, the water formed during the polymerization must be continuously removed. The use of organic solvents with high boiling point, drying agents and reduced pressure led to poly(lactic acid) (PLA) with high molecular weight, directly from the monomer. Tin (II) chloride dihydrate, SnCl2.2H2O, was the best of the catalysts tested as it allowed achieving PLA with a molecular weight close to 80 000 g.mol−1. However, the stereoregurarity control is a severe problem in PLA synthesis by step-growth due to transesterification reactions, which lead to an inversion of the conformation and a decrease of the optical purity of the polymer. Specific rotation measurements were used in this work and showed to be a powerful technique to evaluate the racemization extent. The thermal stability of the PLA samples was evaluated by DSC which exhibits a thermal behaviour similar to the commercial Polylactide. 相似文献
8.
Ji‐Heung Kim Kazunori Emoto Michihiro Iijima Yukio Nagasaki Takao Aoyagi Teruo Okano Yasuhisa Sakurai Kazunori Kataoka 《先进技术聚合物》1999,10(11):647-654
Poly(ethylene glycol‐b‐lactide) possessing a methoxy group at the poly(ethylene glycol) (PEG) chain end and a polymerizable methacryloyl group at the poly(lactic acid) (PLA) chain end (MeO–PEG/PLA–methacryloyl) was prepared by an anionic ring‐opening polymerization of ethylene oxide and DL ‐lactide in tandem manner initiated with a potassium 2‐methoxyethanolate, followed by end‐capping with an excess of methacrylic anhydride. The molecular weight of the obtained polymer was controlled by the initial monomer/initiator ratio, which was confirmed by the combination of gel permeation chromatography and nuclear magnetic resonance analyses. The functionality of the methacryloyl–PLA end was almost quantitative. The MeO–PEG/PLA–methacryloyl (38/35; these numbers in parentheses denote the molecular weights of PEG and PLA segments divided by 100, respectively) formed a core–shell type spherical micelle in aqueous media obtained by a dialysis technique, the cumulant diameter of which was ca. 30 nm with very low polydispersity factor. The methacryloyl group adjacent to the PLA was polymerized in the PLA core of the micelle. The polymerization proceeded thermally with radical initiator and photochemically with photo‐initiator to produce core‐polymerized nanoparticles, which was found by spectroscopic and light‐scattering techniques. Taxol‐incorporated micelles were prepared to entrap Taxol into MeO–PEG/PLA–methyacryloyl block copolymer micelles by the oil/water emulsion method. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
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The ring-opening polymerization of L -lactide (LA) has been initiated by aluminum triflate (trifluoromethanesulfonate) in air using a simple glass tube at 100 °C without desiccation steps and stirring. It was found that the molecular weight of poly(lactic acid) (PLA) was increased by the addition of an alcohol as an initiator to the reaction mixture. The highest number averaged molecular weight, molecular weight distribution, and recovery of the obtained PLA at 100 °C for 6 h were 18,200, 1.20, and 73%, respectively. With the addition of a small percentage of alcohol and a long reaction time of the polymerization method with the re-addition of LA, PLA (ca. 80 wt%) with a higher molecular weight (ca. 30,000) initiated by the added alcohol was produced with PLA (ca. 20 wt%) with a lower molecular weight (ca. 2,000) initiated by impurities such as water, which exist in a monomer, initiator, or catalyst. 相似文献
10.
Jie Song Eunji Lee Byoung‐Ki Cho 《Journal of polymer science. Part A, Polymer chemistry》2013,51(2):446-456
A well‐defined (PEO‐PS)2‐PLA miktoarm terpolymer ( 1 ) was synthesized by stepwise click reactions of individually prepared poly(ethylene oxide) (PEO), polystyrene (PS, polymerized by atom transfer radical polymerization), and polylactide (PLA, polymerized by ring‐opening polymerization) blocks. As characterized by differential scanning calorimetry and small‐angle X‐ray scattering techniques, the terpolymer self‐assembled into a hexagonal columnar structure consisting of PLA/PEO cylindrical cores surrounded by PS chains. In contrast, the ion‐doped sample ( 1‐Li+ ) with lithium concentration per ethylene oxide = 0.2 exhibited a three‐phase lamellar structure, which was attributed to the microphase separation between PEO and PLA blocks and to the conformational stabilization of the longest PLA chain. The two‐phase columnar morphology before the ion doping was used to prepare a nanoporous material. PLA chains in the cylindrical core region were hydrolyzed by sodium hydroxide, producing nanopores with a pore diameter of about 14 nm. The resulted nanoporous material sank to the bottom in water, because of water‐compatible PEO chains on the walls. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
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A one-step pathway has been adopted to fabricate biodegradable polylactide (PLA) hollow spheres by interfacial polymerization
in an oil-in-water emulsion system. The mechanism of sphere formation is suggested with respect to interfacial cross-linking
polymerization and subsequent precipitation of the unreacted PLA macromonomers onto the preformed shells. Their hollow nature
and morphology were verified by transmission electron microscopy and scanning electron microscope characterizations. 相似文献
13.
交联度对原位聚合法制备聚合物胶束性质的影响及相应的空心球制备 总被引:2,自引:0,他引:2
用原位聚合法成功地制备出不同响应温度的温敏性聚乳酸/聚(异丙基丙烯酰胺-co-丙烯酰胺)[P(D,L-LA)/P(NIPAM-co-AM)]核壳胶束. 实验中发现, 壳层的交联剂含量对粒子的尺寸有很大的影响, 当交联剂的摩尔分数从5%提高到15%时, 粒子在25 ℃时的流体力学直径从170.2 nm增加到886.5 nm. 通过对胶束粒子的核进行生物降解, 方便地得到了相应的空心球. 用FTIR监测核的降解过程, 用SEM和AFM检测核降解完全后粒子的外在形貌和内在结构变化. DLS结果表明, 空心球粒子同样具有良好的温度响应性, 其响应温度可通过改变原位聚合时单体AM的含量加以调节. 相似文献
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微米级聚酯醚嵌段共聚物微球的制备及其蛋白包裹研究 总被引:19,自引:0,他引:19
聚酯 醚嵌段共聚物聚 D,L 乳酸 聚乙二醇(Poly DL lactide Polyethyleneglycol,PLA PEG)采用本体聚合法在180℃及-95×10-2MPa条件下制得.光谱分析证实产物结构.采用乳液溶剂蒸发法制备PLA PEG微球,粒径<5μm.以复合乳液技术包裹蛋白.差示扫描量热分析确证PLA PEG有效包裹蛋白.BCA法检测微球蛋白含量.结果表明与均聚物PLA比较,PLA PEG不仅改善了成球条件而且蛋白的包裹效率明显提高. 相似文献
16.
Tadeusz Biedroń Łukasz Pietrzak Przemysław Kubisa 《Journal of polymer science. Part A, Polymer chemistry》2011,49(24):5239-5244
Medium molecular weight poly(L ,L ‐lactide)s (PLA) containing at one chain end ionic group derived from imidazolium ionic liquid (IL) were synthesized by cationic polymerization using hydroxylated IL as initiator. matrix assisted laser desorption/ionization time‐of‐flight analysis confirmed the structure of products (PLA‐IL). Carbon nanotubes (CNT) were dispersed in solution of PLA‐IL in 1,4‐dioxane and significant improvement of stability of suspension was observed by measurements of suspension absorbance. Similar effect was, however, observed also for solutions of PLA which did not contain terminal IL group. CNT samples treated with PLA‐IL and PLA were isolated, thoroughly washed with 1,4‐dioxane and stability of suspensions was again measured. Sample treated with PLA after washing behave similarly to untreated CNT. Stability of suspension of CNT treated with PLA‐IL after washing was considerably higher than that of untreated CNT and the presence of polymer bound to CNT was clearly detectable in scanning electron microscopy images. Results indicate that there is indeed an interaction between end‐group derived from IL and CNT surface as postulated earlier but to observe solely this effect an excess of polymer should be removed, otherwise factors such as increase of viscosity of solution or weak interactions of PLA ester groups with CNT may obscure results. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
17.
Yingchun Yu Raffaele Ferrari Marco Lattuada Giuseppe Storti Massimo Morbidelli Davide Moscatelli 《Journal of polymer science. Part A, Polymer chemistry》2012,50(24):5191-5200
In this work, the preparation of poly(lactic acid) (PLA)‐based degradable nanoparticles (NPs) with tunable hydrophobicity and degradation kinetics via starved emulsion free‐radical polymerization is studied. The synthesis of macromonomers, constituted of a tunable number of lactic acid units functionalized with 2‐hydroxyethyl methacrylate (HEMA), has been performed via bulk ring opening polymerization (ROP) of L, L‐ lactide catalyzed with 2‐ethylhexanoic acid tin (II) salt. Macromonomers were characterized through SEC, NMR, and FTIR and are subsequently polymerized through monomer‐starved semi‐batch emulsion polymerization (MSSEP). The effect on the polymerization process of various emulsifiers on the final diameter and particle size distribution has been studied. The resulting PLA‐based NPs are characterized by a narrow size distribution and a small particle size, down to 25 nm. Finally, a degradation study of selected NPs has been carried out to verify their degradability in aqueous media. It has been demonstrated the complete degradability of these PLA‐based NPs which occurs upon the hydrolysis of the PLA pendant chains leaving poly‐HEMA chains, which, being hydrophilic causes the NPs to dissolve in the aqueous suspension. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
18.
Hyunpyo Lee Jun Beum Park Ji Young Chang 《Journal of polymer science. Part A, Polymer chemistry》2011,49(13):2859-2865
Core‐shell structured nanoparticles of poly(ethylene glycol) (PEG)/polypeptide/poly(D ,L ‐lactide) (PLA) copolymers were prepared and their properties were investigated. The copolymers had a poly(L ‐serine) or poly(L ‐phenylalanine) block as a linker between a hydrophilic PEG and a hydrophobic PLA unit. They formed core‐shell structured nanoparticles, where the polypeptide block resided at the interface between a hydrophilic PEG shell and a hydrophobic PLA core. In the synthesis, poly(ethylene glycol)‐b‐poly(L ‐serine) (PEG‐PSER) was prepared by ring opening polymerization of N‐carboxyanhydride of O‐(tert‐butyl)‐L ‐serine and subsequent removal of tert‐butyl groups. Poly(ethylene glycol)‐b‐poly(L ‐phenylalanine) (PEG‐PPA) was obtained by ring opening polymerization of N‐carboxyanhydride of L ‐phenylalanine. Methoxy‐poly(ethylene glycol)‐amine with a MW of 5000 was used as an initiator for both polymerizations. The polymerization of D ,L ‐lactide by initiation with PEG‐PSER and PEG‐PPA produced a comb‐like copolymer, poly(ethylene glycol)‐b‐[poly(L ‐serine)‐g‐poly(D ,L ‐lactide)] (PEG‐PSER‐PLA) and a linear copolymer, poly(ethylene glycol)‐b‐poly(L ‐phenylalanine)‐b‐poly(D ,L ‐lactide) (PEG‐PPA‐PLA), respectively. The nanoparticles obtained from PEG‐PPA‐PLA showed a negative zeta potential value of ?16.6 mV, while those of PEG‐PSER‐PLA exhibited a positive value of about 19.3 mV. In pH 7.0 phosphate buffer solution at 36 °C, the nanoparticles of PEG/polypeptide/PLA copolymers showed much better stability than those of a linear PEG‐PLA copolymer having a comparable molecular weight. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
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Green and renewable foaming poly(lactic acid) (PLA) represents one of the promising developments in PLA materials. This study is the first to use the lignin graft PLA copolymer (LG‐g‐PLA) to improve the foamability of PLA as a biobased nucleating agent. This agent was synthesized via ring‐opening polymerization of lignin and lactide. The effects of LG‐g‐PLA on cell nucleation induced by the crystallization, rheological behavior, and foamability of PLA were evaluated. Results indicated that LG‐g‐PLA can improve the crystallization rate and crystallinity of PLA, and play a significant nucleation role in the microcellular foam processing of PLA. LG‐g‐PLA improved the foam morphology of PLA, obtaining a reduced and uniform cell size as well as increased expansion ratio and cell density. With the addition of 3 wt% LG‐g‐PLA content, the PLA/LG‐g‐PLA foams increased the compressive strength 1.6 times than that of neat PLA foams. The improved foaming properties of PLA via a biobased nucleating agent show potential for the production and application of green biodegradable foams. 相似文献
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《先进技术聚合物》2018,29(6):1765-1778
Layered double hydroxide‐poly(methylmethacrylate) (LDH‐PMMA) graft copolymers were prepared via activators regenerated by electron transfer for atom transfer radical polymerization. The results showed that the hydrophobicity of LDH‐PMMA was improved by the incorporation of hydrophilic groups. Moreover, poly(lactic acid) (PLA)/LDH‐PMMA nanocomposites were prepared by melt blending to enhance the performances of PLA. The crystallization and mechanical properties of the PLA/LDH‐PMMA nanocomposites were studied by differential scanning calorimetry, tensile testing, and polarized optical microscopy, respectively. Results of mechanical testing showed that the tensile strength, elongation at break, and impact strength of PLA/LDH‐PMMA nanocomposites were increased by 5.64%, 37.95%, and 49.70%, respectively, compared with PLA. The differential scanning calorimetry results indicated that LDH‐PMMA eliminated the cold crystallization of PLA matrix and improved the crystallinity of PLA by 37.26%. The polarized optical microscopy of PLA/LDH‐PMMA nanocomposites demonstrated that LDH‐PMMA increased the crystallization rate of PLA. It was also found that the rheological behaviors of the PLA nanocomposites were significantly enhanced. Based on these results, a new choice for modified LDHs was provided and used as a nucleating agent to improve the properties of PLA. 相似文献