Poly(L-lactide). IX. Hydrolysis in acid media
Poly(L-lactide). IX. Hydrolysis in acid media
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DOI：
10.1002/app.10813
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发表时间：
2002-10-03
影响因子：
3
通讯作者：
Nakahara, K
中科院分区：
文献类型：
--
作者：
Tsuji, H;Nakahara, K
采用淬火和140 ℃退火600 min的方法分别从熔体中制备了非晶和结晶的聚L-乳酸（PLLA）薄膜。在pH 2.0的HCl和DL-乳酸（DLLA）的解决方案（37 degreesC）长达300天，他们的水解进行了研究，并将结果与Pi-LA膜水解在pH 7.4（磷酸盐缓冲溶液）和pH 12（NaOH溶液）。PLLA膜在酸性介质中水解过程中的重量损失和分子量分布的变化揭示了它们的水解主要通过本体侵蚀机制沿膜横截面沿着均匀地进行。此外，PLLA膜在酸性介质中的耐久性与在中性介质中非常相似，但高于在碱性介质中的耐久性。根据数均分子量的变化评价的初始无定形PLLA 0膜的水解速率常数值（k）在pH 2.0的HCl和DLLA溶液中分别为3.0和2.4 × 10（-3）天（-1）。这些k值与pH 7.4的磷酸盐缓冲溶液中的2.6 × 10（-3）天（-1）非常相似。相似的k值和水解300天后可忽略的重量损失反映了水合氢离子和乳酸低聚物和单体对PLLA膜的水解具有不显著的催化作用。增加PLLA膜的初始结晶度增加HCl溶液中的水解速率，而增加PLLA膜的初始结晶度不改变DLLA溶液中的水解速率。差示扫描量热分析结果表明，PLLA链在水解过程中发生结晶，而与水解酸介质和初始结晶度无关。(C)2002 Wiley Periodicals，Inc.
Amorphous and crystallized poly(L-lactide) (PLLA) films are prepared by quenching and annealing at 140degreesC for 600 min, respectively, from the melt. Their hydrolysis is investigated at pH 2.0 in HCl and DL-lactic acid (DLLA) solutions (37degreesC) for up to 300 days, and the results are compared with those obtained for Pi-LA films hydrolyzed at pH 7.4 (phosphate-buffered solution) and pH 12 (NaOH solution). The changes in the weight loss and molecular weight distribution of the PLLA films during hydrolysis in the acid media reveals that their hydrolysis proceeds homogeneously along the film cross section by mainly a bulk erosion mechanism. Moreover, the durability of PLLA films in the acid media is very similar to that in the neutral medium but higher than that in the alkaline medium. The hydrolysis rate constant values (k) of the initially amorphous PLLA0 film evaluated from the changes in the number-average molecular weight were 3.0 and 2.4 x 10(-3) day(-1) at pH 2.0 in the HCl and DLLA solutions, respectively, These k values are very similar to 2.6 x 10(-3) day(-1) at pH 7.4 in the phosphate-buffered solution. The similar k values and the negligible weight loss after the hydrolysis for 300 days reflect that the hydronium ions and the lactic acid oligomers and monomers have insignificant catalytic effects on the hydrolysis of the PLLA films. Increasing the initial crystallinity of the PLLA film increases the hydrolysis rate in the HCl solution, whereas increasing the initial crystallinity of the PLLA film does not alter the hydrolysis rate in the DLLA solution. The differential scanning calorimetry results show that the crystallization of PLLA chains occurs during the hydrolysis, irrespective of the hydrolysis acid media and the initial crystallinity. (C) 2002 Wiley Periodicals, Inc.