降解可控乳酸类聚合物

聚乳酸作为生物医用材料，其降解性能最为人们关注。根据降解性能的不同，其应用也有不同的用途。本文从共聚和共混两方面综述了聚乳酸在降解可控性方面研究的最新进展，对未来的工作进行了展望。     

溶剂诱导的聚乳酸/聚乳酸衍生物共结晶行为

通过溶液浇铸法制备不同组分的左旋聚乳酸(PLLA)和聚(L-2-羟基-3-甲基丁酸)(PL-2H3MB)共混物.运用差示扫描量热仪(DSC)、偏光显微镜(POM)、广角X射线衍射(WAXD)和热重分析仪(TGA)分析共混物的结晶、熔融行为和热稳定性.通过观察到DSC加热曲线中新的熔融峰判断PLLA和PL-2H3MB共晶...     

聚乳酸共混体系的研究进展

聚乳酸是人工合成的可生物降解的热塑性脂肪族聚酯 ,是一种环境友好的材料 ,逐渐成为人们研究的热点。本文根据聚乳酸共混体系中另一组分的生物降解性 ,将聚乳酸共混体系分为完全可生物降解共混体系和部分可生物降解共混体系两类。针对体系的相容性和结晶结构以及在提高PLA的性能和降低成本等方面 .综述了聚乳酸共混体系的最新研究进展 ,并对其发展动态进行了简要介绍     

Poly(lactic acid) Synthesis in Solution Polymerization

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.     

生物基超韧聚乳酸复合材料的制备与性能

采用来源于可再生资源的聚醚酰胺弹性体（PEBA）增韧聚乳酸（PLA）制备超韧聚乳酸（PLA/PEBA-GMA）复合材料.为了提高PEBA与PLA之间的相容性,选择极性单体甲基丙烯酸缩水甘油酯（GMA）、共接枝单体乙烯基吡咯烷酮（NVP）及引发剂过氧化二异丙苯（DCP）对PEBA进行接枝改性制备PEBA-GMA.研究了接枝单体组分的用量（m/g）对PLA/PEBA-GMA复合材料性能的影响.研究发现,随着接枝单体组分用量的提高,复合材料的缺口冲击强度逐渐增大,当接枝单体组分GMA,NVP和DCP的用量分别为2.5,2.5和0.25 g时,复合材料的冲击强度高达88.6 kJ/m²,断裂伸长率为164.1%.研究表明,在熔融共混过程中,聚乳酸的端基（—OH和—COOH）与PEBA-GMA上环氧基团发生反应,有效改善两相间的界面相容性,随着接枝单体组分比例的提高,分散相PEBA-GMA的粒子尺寸逐渐减小且分布均匀.     

Chemical modification of poly(lactic acid) and its use as matrix in poly(lactic acid) poly(butylene adipate-co-terephthalate) blends

Poly(lactic acid), PLA, was chemically modified with maleic anhydride (MA) by reactive extrusion. The effect of this modification on molar mass (MM) and acidity was assessed by means of size-exclusion chromatography (SEC) and titration, respectively. PLA MM decreased in the presence of MA solely and of MA and peroxide. Reduction in MM was monitored by the increase in acidity. PLA blends containing poly(butylene adipate-co-terephthalate) (PBAT) were prepared through different mixing protocols, PLA/PBAT, PLA-g-MA/PBAT and PLA/PBAT/MA/peroxide (PLA/PBAT in situ). SEC results and rheological properties revealed reduction in MM and viscosity of the modified blends. PLA/PBAT presented increase in MM and bimodal MM distribution. The calculated interfacial tension was significantly lower for the modified blends, despite the lower average particle area of PLA/PBAT. Surprisingly, the modified blends presented higher yield strength than that predicted by the rule of mixtures, which might indicate interfacial reactions.     

Blends of Poly（lactic acid） with Thermoplastic Acetylated Starch

Blends of poly(lactic acid)(PLA) and thermoplastic acetylated starch(ATPS) were prepared by means of the melt mixing method. The results show that PLA and ATPS were partially miscible, which was confirmed with the measurement of Tg by dynamic mechanical analysis(DMA) and differrential scanning calorimetry(DSC). The mechanical and thermal properties of the blends were improved. With increasing the ATPS content, the elongation at break and impact strength were increased. The elongation at break increased from...     

基于聚乙二醇结构调控高分子量聚乳酸立构复合体系的结晶行为

设计合成了梳形聚(聚乙二醇甲醚丙烯酸酯)(PPEGA)及其与聚乙二醇(PEG)的嵌段共聚物(PEG-b-PPEGA).通过与高分子量左旋聚乳酸(PLLA)和右旋聚乳酸(PDLA)共混探究了PEG不同的结构对PLA立构复合体系(sc-PLA)结晶的影响.结果 表明线形PEGA和PEG能与sc-PLA完全相容,两者均能促进...     

不同催化剂作用下聚乳酸/聚碳酸亚丙酯的酯交换反应

选用辛酸亚锡[Sn(Oct)₂]和钛酸四丁酯(TBT)作为聚乳酸(PLA)/聚碳酸亚丙酯(PPC)的酯交换反应催化剂, 研究了溶液条件下单一催化剂及复合催化剂对PLA/PPC酯交换反应的催化作用. 通过对反应产物的分子结构、 热力学及流变学行为进行分析, 结果发现, 无论在单一催化剂还是复合催化剂作用下, PLA与PPC分子间均发生了酯交换反应, 同时伴随着断链反应. 其中, 当Sn(Oct)₂作为单一催化剂或Sn(Oct)₂/TBT作为复合催化剂时, 样品更倾向发生断链反应而非显著的酯交换反应. 进一步分析纯样品在催化剂Sn(Oct)₂或TBT作用下的反应情况, 结果发现, PPC在反应最初阶段以高分子量的分子链断链为主, 且会发生明显的解拉链降解, 从而导致PLA/PPC在等质量比时酯交换反应程度不高, 这为今后更好地研究PLA/PPC酯交换反应提供了思路.     

Compatibility and phase structure of binary blends of poly(lactic acid) and glycidyl methacrylate grafted poly(ethylene octane)

This work study is the compatibility, phase structure, and component interaction of poly(lactic acid) (PLA) and glycidyl methacrylate grafted poly(ethylene octane) (GMA-g-POE denoted as mPOE) blend by Fourier transform infrared (FTIR) spectra, dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), and wide-angle X-ray diffraction (WAXD), respectively. All the binary blend compositions exhibit two distinct glass transition temperatures corresponding to the mPOE-rich and PLA-rich phases, respectively. Moreover, these two peaks approach each other with increasing mPOE content, indicating partial compatibility between the PLA and mPOE. Chemical reactions between the end carboxyl groups of the PLA and epoxy groups of the mPOE are considered as the driving force of the enhanced compatibility. They lead to an increase in viscosity of the blends and a decrease in the structural symmetry of PLA. This result brings about a decrease in the spherulite growth rate and the degree of crystallinity. Glass transition temperature (T_g) depression of mPOE is attributed to the negative pressure imposed on the dispersed rubber phase, resulting from differential contraction due to the thermal shrinkage mismatch upon cooling from the melt state. The negative pressure in the dispersed particles, in turn, would cause a dilational effect for the matrix ligament between the particles, and therefore increases the ductility and toughness of PLA.     

退火过程中聚乳酸中间相的形成和结构演化

采用淬火法制备聚乳酸(PLA)非晶薄膜,并利用原位显微红外光谱在线研究PLA非晶薄膜在不同退火温度下的结构演化.结果表明,PLA非晶薄膜存在一个临界结晶温度,当退火温度高于临界结晶温度时,PLA非晶薄膜可以通过分子链的局部调整实现冷结晶,反之,不能发生冷结晶;在冷结晶过程中先出现中间相,随后发生中间相-晶体相的转变;中间相是通过分子链的构象调整和分子链间的堆砌调整产生的,退火温度越高,中间相出现得越早,最终得到的晶体结构越规整.     

聚乳酸热塑性弹性体的研究进展

热塑性弹性体(TPE)是一类应用领域非常广泛且极具发展潜力的高分子材料,然而目前TPE品种所选用的原料(包括单体或聚合物)绝大部分都是源于石油基不可再生资源。作为一种极具潜力替代石油基高分子的生物基脂肪族聚酯材料,聚乳酸(PLA)具有原料来源丰富并可再生、生物降解性良好、强度和模量高等优点,因此聚乳酸TPE的研究吸引了国内外学者广泛的关注。本文综述了PLA嵌段共聚物型TPE和PLA基动态硫化热塑性弹性体(TPV)的最近的研究进展,详细阐述了它们的制备路线以及材料的性能,最后指出了当前PLA热塑性弹性体研究中存在的不足。     

聚丙烯酸在纳米TiO2表面吸附行为的研究

讨论了聚丙烯酸在纳米TiO₂水悬浮体系中的吸附行为.红外光谱分析和吸附实验结果表明,纳米TiO₂通过氢键吸附PAA.PAA吸附量随着浓度的升高而增大直至饱和吸附量,且分子量越大,饱和吸附量越大.pH值增大,则饱和吸附量减小.在相同条件下,表面吸附层的厚度随PAA分子量、浓度和pH值增大而增大.这是由PAA在颗粒表面构型的变化所致.吸附PAA后的纳米TiO₂的表面电荷密度和ζ电位发生变化,pHiep值向低值方向移动.表面吸附自由能的计算结果说明,PAA在纳米TiO₂表面的吸附是自发过程.     

Effect of pH on Poly(acrylic acid) Solution Polymerization

The free-radical redox-initiated aqueous solution polymerization of fully and partially neutralized acrylic acid was carried out at room temperature under full exposure to air. The effect of neutralization degree on the polymerization rate and product properties was studied. Increasing neutralization of the reaction mixture with sodium hydroxide resulted in greater conversion of acrylic acid to sodium acrylate. The rate of polymerization, determined from a gravimetric off-line water removal technique, was shown to decrease significantly with decreasing degree of neutralization. Molecular weight also decreased with decreasing degree of neutralization. The glass transition temperature and hydrophilicity of the polymer product decreased with increasing degree of neutralization. In-line infrared monitoring was also used to monitor the reaction progress and was shown to be an effective tool for this purpose.     

Pervaporation of alcohol-toluene mixtures through polymer blend membranes of poly(acrylic acid) and poly(vinyl alcohol)

Homogeneous membranes were prepared by blending poly(acrylic acid) with poly(vinyl alcohol). These blend membranes were evaluated for the selective separation of alcohols from toluene by pervaporation. The flux and selectivity of the membranes were determined both as a function of the blend composition and of the feed mixture composition. The results showed that a polymer blending method could be very useful to develop new membranes with improved permselectivity. The pervaporation properties could be optimized by adjusting the blend composition. All the blend membranes tested showed a decrease in flux with increasing poly(vinyl alcohol) content for both methanol—toluene and ethanol—toluene liquid mixtures. The alcohols permeated preferentially through all tested blend membranes, and the selectivity values increased with increasing poly(vinyl alcohol) content. The pervaporation characteristics of the blend membranes were also strongly influenced by the feed mixture composition. The fluxes increased exponentially with increasing alcohol concentration in the feed mixtures, whereas the selectivities decreased for both liquid mixtures.     

Binding of a surfactant counterion to low-charge-density poly(acrylic acid) and poly(methacrylic acid)

The binding of a cationic surfactant, dodecylpyridinium (C12Py) chloride, with a low-charge-density poly (methacrylic acid) (PMA) was investigated in buffer solutions under the condition of constant pH. The binding isotherms with PMA consisted of two and three steps at a pH lower and higher than 3.2, respectively. Bindings in the first step were independent of pH and this step was considered to correspond to the solubilization of the hydrocarbon chains of C12Py into the nonpolar region of the compact form of PMA. This is the indication of the compact form from the binding isotherm. At pH higher than 3.2, the second step was discriminated and it depended on the pH. In the third step, a sharp rise in the degree of binding (β) was observed accompanying the solubilization of the precipitates of the PMA–C12Py complex. The binding with poly(acrylic acid) (PAA) and PMA in conventional unbuffered NaCl solutions was also examined and the pH profile of the solution during the binding process was determined. In the case of unbuffered NaCl solutions, the binding with PAA took place cooperatively at the critical association concentration (cac). The binding isotherm consisted of two steps and the pH decreased with the increase in β. The binding isotherm of PMA, on the other hand, consisted of three steps: the pH decreased slightly in the first step and considerably in the second step with the increase in β but it increased with β in the third step, exhibiting a pH minimum around 3.2. The binding in the first step coincided with that obtained in the buffered solutions. Linear relationships between β and the pH were found for both polymers. In the case of PMA, no cac was observed in both buffered and unbuffered NaCl solutions. Received: 24 January 2001 Accepted: 23 May 2001     

苹果酸基脂肪共聚酯反应性共混制备超韧聚乳酸共混物

通过反应性共混使聚乳酸(PLA)与增韧剂原位生成接枝共聚物,可增强界面相互作用,有效提高不相容共混物的韧性.本研究将聚(癸二酸/苹果酸-co-丁二醇/丙二醇)酯(PBSePM)在六亚甲基二异氰酸酯(HDI)作用下与PLA反应性共混制备了PLA/PBSePM共混物.重点研究了HDI对PLA/PBSePM共混物的力学性能、...     

Preparation and characterization of poly(acrylic acid)-based nanoparticles

The present investigation describes the synthesis and characterization of nanoparticles based on poly(acrylic acid) (PAA) intramolecularly cross-linked with diamine, 2,2′-(ethylenedioxy)bis(ethylamine), using water-soluble carbodiimide. The aqueous colloid dispersions of nanoparticles were clear or mildly opalescent depending on the ratio of cross-linking, pH of the solution, and the molecular weight of PAA, finding consistent with values of transmittance between 3% and 99%. The structure was determined by nuclear magnetic resonance spectroscopy, and the particle size was identified by dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. It was found that particle size depends on the pH, and at a given pH, it was caused by the ratio of cross-linking and the molecular weight of PAA. Particle size measured by TEM varied in the range of 20 and 80 nm. In the swollen state, the average size of the particles measured by DLS was in the range of 35–160 nm.     

pH-effects in the complex formation of polymers I. Interaction of poly(acrylic acid) with poly(acrylamide)

The effects of polymer concentration, molecular weight of poly(acrylic acid) (PAA), addition of sodium, potassium, ammonium and copper (II) chlorides on the complex formation ability of the system PAA-poly(acrylamide) (PAAM) have been studied in aqueous solutions. The critical pH values of the complexation were determined in different conditions. The complex formation ability of PAAM is compared with other non-ionic polymers. It was shown that an increase in polymers concentration, molecular weight of PAA and ionic strength favours the complexation and shifts the critical pH values to the higher pH region. An addition of CuCl₂ to the mixture of two polymers enhances the complexation drastically due to the formation of triple complexes.     

Poly (acrylic acid) microchannel modification for the enhanced resolution of catecholamines microchip electrophoresis with electrochemical detection

A new modification of glass electrophoresis microchips based on poly (acrylic) acid immobilization has been performed. It is based on the reaction of PAA with an amine functionalized surface, obtained through the bifunctional reagent 3-aminopropyl triethoxysilane. Parameters affecting all the three steps involved: surface activation, silanization and polymer immobilization were optimized employing soda-lime glass plates. Characterization by SEM and XPS was carried out. Application of the modified microchips to the separation of a model system: dopamine (D), epinephrine (E) and norepinephrine (NE), that on the other hand are of high clinical relevance was performed employing amperometric detection. Modification is necessary for obtaining partial resolution of all the three analytes in a microchip with an effective separation length of 30 mm. Situation changes from no resolution (Rs) at all (only one peak was achieved for the mixture) to a partial resolution (Rs D–NE and Rs NE–E are 0.25 and 0.24 respectively). Microchips with 60 mm of separation channel were also modified, implying this procedure a resolution enhancement (Rs of 0.49 and 0.28 for D–NE and NE–E respectively), even when methanol is employed as organic modifier (Rs values of 0.70 (D–NE) and 0.66 (NE–E) for a 3% MeOH).