丙交酯的合成与聚合

丙交酯是由乳酸合成聚乳酸的中间体,采用新型La Ti复合氧化物催化乳酸合成丙交酯,粗丙交酯经乙酸乙酯纯化后,差热分析仪测得其熔点为126 4℃,纯化后的丙交酯在一定条件下,经辛酸亚锡引发,开环聚合成聚乳酸,并用红外光谱和差热分析仪对聚乳酸进行了表征。     

Shape memory effect of poly(L‐lactide)‐ based polyurethanes with different hard segments

A series of biodegradable polylactide‐based polyurethanes (PLAUs) were synthesized using PLA diol (M_n = 3200) as soft segment, 4,4′‐diphenylmethane diisocyanate (MDI), 2,4‐toluene diisocyanate (TDI), and isophorone diisocyanate (IPDI) as hard segment, and 1,4‐butanediol as chain extender. The structures and properties of these PLAUs were studied using infrared spectroscopy, differential scanning calorimetry, tensile testing, and thermomechanical analysis. Among them, the MDI‐based PLAU has the highest T_g, maximum tensile strength, and restoration force, the TDI‐based PLAU has the lowest T_g, and the IPDI‐based PLAU has the highest tensile modulus and elongation at break. They are all amorphous. The shape recovery of the three PLAUs is almost complete in a tensile elongation of 150% or a twofold compression. They can keep their temporary shape easily at room temperature (20 °C). More importantly, they can deform and recover at a temperature below their T_g values. Therefore, by selecting the appropriate hard segment and adjusting the ratio of hard to soft segments, they can meet different practical demands for shape memory medical devices. Copyright © 2007 Society of Chemical Industry     

D,L-丙交酯的合成与纯化

以D,L-乳酸为原料,在催化剂存在下通过脱水环化合成D,L-丙交酯,研究了反应过程中催化剂用量、脱水温度及稀释剂等因素对D,L-丙交酯产率的影响。用重结晶法对粗产物进行纯化,制备出高产率、高纯度的D,L-丙交酯。实验结果表明,采用二丁基氧化锡为催化剂,最佳催化剂用量(质量分数)为1 5%,最佳脱水温度为140℃,且在反应中加入稀释剂可以显著提高D,L-丙交酯的粗产率;乙醇是理想的重结晶溶剂,粗产物经多次纯化后,可获得总产率达37 3%的纯D,L-丙交酯。     

多支化聚乳酸的制备及其对聚乳酸结晶效果的影响

采用水解-缩聚两步法制备聚环氧基倍半硅氧烷微球(PESQ),以其为支化核心,通过辛酸亚锡催化丙交酯在熔融态开环形成支链制备多支化聚乳酸(m-PLLA),利用FTIR,1H NMR,GPC等方法表征m-PLLA的结构。表征结果表明,聚乳酸(PLA)成功接枝到PESQ上,且随丙交酯添加量的增加,m-PLLA先增加支链长度,后增加支链数目,最后支链长度和数目同时增加。考察了m-PLLA作为成核剂对PLA结晶过程的影响。实验结果表明,添加1.0%(w)的m-PLLA10时,PLA的冷结晶温度从121.2℃降至113.4℃,结晶度从15.7%升至31.1%,平均球晶直径从100μm细化至15μm,优于添加等量滑石粉的PLA。     

Novel materials through stereocomplexation

Summary Both (–)- and (+)-poly(lactide) (PLA) crystallize into a stereocomplex with a melting point that is 50 °C higher than that of crystals of the same-handed enantiomers. According to Boyer et al. [Polym. Prepr., 36 (1995) 87] and Jiang et al. [J. Am. Chem. Soc., 117 (1995) 7037], alternating isotactic propylene-CO-copolymers (P(P-alt-CO)) also form a stereocomplex with a higher melting point (60 °C). Force-Field-simulated structures for both polymer systems were found to agree well with X-ray data, irrespective of whether they had a chiral or racemic packing. The almost similar results for both stereocomplexes indicate that they might form a mixed stereocomplex of (–)-PLA and (+)-P(P-alt-CO). In acetonitrile, both enantiomers of an AB block copolymer derivative, poly(lactide)-poly(ethyleneglycol) (PLA-PEG); were found to crystallize exclusively into a racemic lattice. The influence of racemic packing on self-assembly of the two-block copolymer was analyzed by atomic-force microscopy. An equimolar mixture of (–)- and (+)-PLA-PEG formed spherical particles through stereocomplexation, in contrast to chiral block copolymers that formed large crystal needles and long rods.     

Allylamine plasma‐polymerization on PLLA surface evaluation of the biodegradation

Biodegradation of poy(L ‐lactide) (PLLA) films and filaments recovered with hydrophilic layer (contact angle = 14°, surface energy γ_s = 70.9 mJ m^?2) from allylamine plasma polymerization was investigated under aerobic conditions in sludge. XPS and FTIR‐ATR analysis of the plasma layer showed 14.4% N and 16.6% O mainly as amide group. Optical microscopy showed much bacteria colonies on treated PLLA surface than on untreated one. Weight loss and oxygen consumption after 65 days were 4–5% and 4 mg h^?1 per gram polymer respectively. The fact that biodegradation lag‐phase for treated PLLA was released quicker (7 days) than untreated one (14 days), could be related to the presence of hydrophilic plasma layer that improved swelling‐dissolution of hydrolyzed molecular fragments. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007