POLYLACTIDE STEREOCHEMISTRY - EFFECT ON ENZYMATIC DEGRADABILITY
POLYLACTIDE STEREOCHEMISTRY - EFFECT ON ENZYMATIC DEGRADABILITY
复制标题
DOI：
10.1021/ma00081a030
复制
发表时间：
1994-01-31
期刊：
影响因子：
5.5
通讯作者：
GROSS, RA
中科院分区：
文献类型：
--
作者：
REEVE, MS;MCCARTHY, SP;GROSS, RA
使用辛酸亚锡作为催化剂，由(D)-丙交酯和(L)-丙交酯的混合物制备％L重复单元含量为100(PLA-100)、99、96、94、92、85、80、75、70、50和0的聚丙交酯(PLG)。这些样品的PLA薄膜通过溶液流延制备，然后在75℃下退火36小时结晶。通过差示扫描量热法和广角 X 射线散射测量，观察到 %L 组成在 85% 至 100% 之间的 PLA 晶序发生巨大变化。 PLA 薄膜与蛋白酶 K（来自 Tritirachium album）一起孵育，以确定酶催化的薄膜重量损失和初始表面降解速率。后者的速率值是通过监测pH值变化获得的。与 (D)-PLA 相比，蛋白酶 L 优先降解 (L)-PLA。 PLA-92 的薄膜失重和初始表面降解均达到最佳速率。此外，相对于 PLA-85 和 PLA-94，PLA-92 的薄膜失重率大幅增加，表明 8% D 重复单元的引入导致了结晶顺序的严重破坏。比较结晶度百分比为 57% 和 27% 的 PLA-100 的降解率表明，较低结晶度样品的薄膜重量损失和初始表面降解率均大幅增加。相对于 PLA-92，PLA-75 和 PLA-50 的初始表面降解率出乎意料地高。相比之下，发现 PLA 立体化学组合物的薄膜失重率值从 92% L 快速下降到 50% L。然而，从定性上来说，初始表面降解率和薄膜失重测量值是一致的。膜失重超过 25% 的酶孵育中残留的 PLA-100 显示出分子量几乎没有变化，并且 Delta H-f 值增加，正如对膜表面的酶催化膜降解过程所预期的那样，该降解过程优先发生在无定形区域。
Polylactide (PLG) with % L repeat unit contents of 100 (PLA-100), 99, 96, 94, 92, 85, 80, 75, 70, 50, and 0 were prepared from mixtures of (D)- and (L)-lactide using stannous octanoate as catalyst. PLA films of these samples were prepared,by solution casting and then annealing at 75 degrees C for 36 h to crystallize. Large changes in the crystalline order for PLA with % L compositions between 85 and 100% were observed by differential scanning calorimetry and wide-angle X-ray scattering measurements. The PLA films were incubated with proteinase K (from Tritirachium album) to determine enzyme-catalyzed rates of both film weight loss and initial surface degradation. The latter rate values were obtained by monitoring pH changes. Proteinase L preferentially degraded (L)-PLA as opposed to (D)-PLA. Optimal rates for both film weight loss and initial surface degradation were found for PLA-92. In addition, a large increase in the film weight loss rate for PLA-92 relative to both PLA-85 and PLA-94 indicates that a critical disruption of the crystalline order resulted from the introduction of 8% D repeat units. Comparison of degradation rates for PLA-100 at percent crystallinities of 57 and 27% showed large increases in both film weight loss and initial surface degradation rates for the lower crystallinity sample. Initial surface degradation rates were unexpectedly high for PLA-75 and PLA-50 relative to PLA-92. In contrast, a rapid decline in film weight loss rate values was found for PLA stereochemical compositions from 92 to 50% L. However, qualitatively, the rates of initial surface degradation and film weight loss measurements are in agreement. Residual PLA-100 from enzyme incubations where film weight loss exceeded 25% showed little change in molecular weight and increased Delta H-f values as was expected for an enzyme-catalyzed film degradation process at the: film surface which occurs preferentially at amorphous domains.