二丁基镁引发内酯开环聚合制备脂肪族聚酯

以对人体无毒的二丁基镁作引发剂引发内酯开环聚合制备一系列脂肪族聚酯的均聚物、无规共聚物、两嵌段、三嵌段共聚物，用NMR，GPC，DSC，XRD等对其结构和性能进行表征，以期用作药物载体。     

Comparison of the degradability of poly(lactide) packages in composting and ambient exposure conditions

The adoption of biodegradable polymeric materials is increasing in food and consumer goods packaging applications, due to concerns about the disposal of petroleum‐based polymers and the increasing cost of petroleum‐based polymer resins. Currently, poly(lactide) (PLA) polymers are the biggest commercially available bio‐based polymeric packaging materials. As the main motivation for adopting biopolymers is environmental, there is a need to address the degradability and environmental performance of biodegradable packages. The aim of this study was to investigate and compare the degradation of two commercially available biodegradable packages made of PLA under real compost conditions and under ambient exposure, using visual inspection, gel permeation chromatography, differential scanning calorimetry and thermal gravimetric analysis. A novel technique to study and track the degradability of these packages under real compost conditions was used. Both packages were subjected to composting and ambient exposure conditions for 30 days, and the degradation of the physical properties was measured at 1, 2, 4, 6, 9, 15 and 30 days. PLA bottles made of 96% l ‐lactide exhibited lower degradation than PLA delicatessen (‘deli’) containers made of 94% l ‐lactide, mainly due to their highly ordered structure and, therefore, their higher crystallinity. The degradation rate changed as the initial crystallinity and the l ‐lactide content of the packages varied. Temperature, relative humidity and pH of the compost pile played an important role in the rate of degradation of the packages. First‐order degradation kinetics and linear degradation trends were observed for both packages subjected to composting conditions. Copyright © 2006 John Wiley & Sons, Ltd.     

mPEG⁃PLA嵌段共聚物及其胶束的降解行为研究

采用开环聚合法制备了聚乙二醇单甲醚（mPEG）与D,L⁃丙交酯的嵌段共聚物,并以此共聚物为载体制备了紫杉醇胶束,研究了mPEG⁃聚丙交酯（PLA）与载药胶束（DMs）在不同条件下的降解特点。结果表明,在低温下（4 ℃）,mPEG⁃PLA聚合物和DMs均能长时间（24个月）保持稳定,未发生明显降解;当温度升高,mPEG⁃PLA和DMs降解速度明显增加,但降解机理有所不同,这种差异在40 ℃以上的环境中更明显;mPEG⁃PLA聚合物的高温（60 ℃）降解以链段内部无规则断裂为主,分子量显著降低;DMs在高温（60 ℃）下则更多遵循“末端降解机理”,生成更多的丙交酯和乳酸。     

Protonated Phosphazenes: Structures and Hydrogen‐Bonding Organocatalysts for Carbonyl Bond Activation

The synthesis and application of protonated phosphazeniums as hydrogen‐bond donor groups was demonstrated in the solid state and in solution. In particular, their catalytic activity was shown in the activation of the carbonyl group within cyclic esters, using a benchmark reaction, that is, in the ring‐opening polymerization of lactide and valerolactone, in the presence of a basic co‐catalyst. The reactions proceed differently depending on monomers and/or phosphazenium salts. The impact of catalysts and reactants steric hindrance upon the outcome of the reaction is then highlighted and discussed.

     

Synthesis,physical properties,and crystallization of optically active poly(L‐phenyllactic acid) and poly(L‐phenyllactic acid‐co‐L‐lactic acid)

Optically active poly(L ‐phenyllactic acid) (Ph‐PLLA), poly(L ‐lactic acid) (PLLA), and poly(L ‐phenyllactic acid‐co‐L ‐lactic acid) with weight‐average molecular weight exceeding 6 × 10³ g mol^?1 were successfully synthesized by acid catalyzed direct polycondensation of L ‐phenyllactic acid and/or L ‐lactic acid in the presence of 2.5–10 wt % of p‐toluenesulfonic acid. Their physical properties and crystallization behavior were investigated by differential scanning calorimetry, thermogravimetry, and polarimetry. The absolute value of specific optical rotation ([α]) for Ph‐PLLA (?38 deg dm^?1 g^?1 cm³) was much lower than that of [α] for PLLA (?150 deg dm^?1 g^?1 cm³), suggesting that the helical nature was reduced by incorporation of bulky phenyl group. PLLA was crystallizable during solvent evaporation, heating from room temperature, and cooling from the melt. Incorporation of a very low content of bulky phenyllactyl units even at 4 mol % suppressed the crystallization of L ‐lactyl unit sequences during heating and cooling, though the copolymers were crystallizable for L ‐phenylactyl units up to 6 mol % during solvent evaporation. The activation energy of thermal degradation (ΔE_td) for Ph‐PLLA (200 kJ mol^?1) was higher than that for PLLA (158 kJ mol^?1). The ΔE_td for the copolymers increased with an increase in L ‐phenyllactyl unit content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

丙交酯制备工艺的研究现状

丙交酯是以乳酸为原料制备高分子量聚乳酸的中间体,因此丙交酯的收率是影响聚乳酸大规模生产及其生产成本的关键因素.对乳酸及丙交酯的结构特点、乳酸合成丙交酯的工艺及影响丙交酯产率的主要因素进行了论述,进而提出了提高丙交酯产率应采取的相应措施.     

丙交酯中残存乳酸和水的定量测定

定量地知道丙交酯中残存的乳酸和水的量,有助于在丙交酯的提纯和聚合中对工艺过程进行更精密的控制。用甲醇钠非水滴定法、卡尔－费休法对熔点为１２７℃的丙交酯样品进行了定量分析试验,测出残存的乳酸和水的质量分数分别为０．０９％和０．０７％ 左右,回收率分别为９８．６４％ ～１０１．２％ 和９８．７４％ ～１０１．１％ 。实验表明,这两种方法可分别定量测定丙交酯中残存乳酸和水,且简捷实用。     

Biodegradable membranes for the controlled release of progesterone. 1. Characterization of membrane morphologies coagulated from PLGA/progesterone/DMF solutions

Biodegradable membranes containing progesterone as a drug were prepared from ternary, poly(d,l‐lactide‐co‐glycolide)/progesterone/dimethylformamide, solutions. The homogeneous solutions, after cast on glass plates, were solidified to result in a solid membrane structure by three different solvent‐removal processes: solvent evaporation under vacuum, solvent extraction via immersion into the nonsolvent bath, or vapor exposure at high humidity condition. Impregnation characteristics of progesterone in the prepared membranes varied significantly, depending on the removal processes used. When a cast solution was solidified by exposure at the environment of 70% relative humidity, progesterone was separated from a membrane structure with the morphology of flake‐like shapes, and thermal analysis of the prepared membrane showed the clear, endothermic peak of the drug. Vitrification of a cast solution by solvent evaporation under vacuum induces both the uniform drug dispersion in the polymer matrix, with the drug forming spherical structures, and the strong interaction between the drug and the matrix, as identified by a broadened melting endotherm of the drug. When coagulated at thermodynamic nonequilibrium conditions through rapid exchange between dimethyformamide and water, the cast solution film results in a membrane structure consisting of the drug distributed nonuniformly in the polymer matrix. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 60–67, 2000     

Crystallization behavior and mechanical properties of bio‐based green composites based on poly(L‐lactide) and kenaf fiber

Bio‐based polymer composite was successfully fabricated from plant‐derived kenaf fiber (KF) and renewable resource‐based biodegradable polyester, poly(L ‐lactide) (PLLA), by melt‐mixing technique. The effect of the KF weight contents (0, 10, 20, and 30 wt %) on crystallization behavior, composite morphology, mechanical, and dynamic mechanical properties of PLLA/KF composites were investigated. It was found that the incorporation of KF significantly improves the crystallization rate and tensile and storage modulus. The crystallization of PLLA can be completed during the cooling process from the melt at 5°C/min with the addition of 10 wt % KF. It was also observed that the nucleation density increases dramatically and the spherulite size drops greatly in the isothermal crystallization with the presence of KF. In addition, with the incorporation of 30 wt % KF, the half times of isothermal crystallization at 120°C and 140°C were reduced to 46.5% and 28.1% of the pure PLLA, respectively. Moreover, the tensile and storage modulus of the composite are improved by 30% and 28%, respectively, by the reinforcement with 30% KF. Scanning electron microscopy observation also showed that the crystallization rate and mechanical properties could be further improved by optimizing the interfacial interaction and compatibility between the KF and PLLA matrix. Overall, it was concluded that the KF could be the potential and promising filler for PLLA to produce biodegradable composite materials, owing to its good ability to improve the mechanical properties as well as to accelerate the crystallization of PLLA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Aging of poly(lactide)/poly(ethylene glycol) blends. Part 2. Poly(lactide) with high stereoregularity

Blending poly(ethylene glycol) (PEG) with poly(lactide) (PLA) decreases the T_g and improves the mechanical properties. The blends have lower modulus and increased fracture strain compared to PLA. However, the blends become increasingly rigid over time at ambient conditions. Previously, it was demonstrated that a PLA of lower stereoregularity was miscible with up to 30 wt% PEG. Aging was due to slow crystallization of PEG from the homogeneous amorphous blend. Crystallization of PEG depleted the amorphous phase of PEG and gradually increased the T_g until aging essentially ceased when T_g of the amorphous phase reached the aging temperature. In the present study, this aging mechanism was tested with a crystallizable PLA of higher stereoregularity. Changes in thermal transitions, solid state structure, and mechanical properties were examined over time. Blends with up to 20 wt% PEG were miscible. Blends with 30 wt% PEG could be quenched from the melt to the homogenous amorphous glass. However, this composition phase separated at ambient temperature with little or no crystallization. Changes in mechanical properties during phase separation reflected increasing rigidity of the continuous PLA-rich phase as it became richer in PLA. Construction of a phase diagram for blends of higher stereoregular PLA with PEG was attempted.