Degradation mechanism and kinetics of thermosensitive polyacrylamides containing lactic acid side chains
Degradation mechanism and kinetics of thermosensitive polyacrylamides containing lactic acid side chains
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DOI：
10.1021/ma034381n
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发表时间：
2003-10-07
期刊：
影响因子：
5.5
通讯作者：
Hennink, WE
中科院分区：
文献类型：
--
作者：
Neradovic, D;van Steenbergen, MJ;Hennink, WE
聚（N-异丙基丙烯酰胺-共-N-（2-羟丙基）甲基丙烯酰胺乳酸酯）（聚（NIPAAm-共-HPMAm-乳酸酯））作为热敏嵌段和聚（乙二醇）（PEG）作为亲水嵌段的二嵌段共聚物在温度敏感嵌段的浊点（CP）以上形成聚合物胶束。这些胶束的不稳定发生在乳酸侧链水解时。在这里，我们报告的HPMAm-单（二）乳酸酯单体及其共聚物与NIPAAm的降解动力学。单体和聚合物在其可溶状态下（因此低于其CP）的降解遵循正常的酯水解行为：降解速率随温度、pH值（从pH 7.5至11）和介质的介电常数而增加。在CP以上，其中聚合物处于沉淀状态，由于沉淀聚合物的局部环境的介电常数的降低而发生聚合物降解的显著延迟。该研究表明，可以预测NIPAAm-共-HPAIAm-乳酸酯共聚物中HPMAm的形成速率，这导致聚合物的总体亲水性增加和基于聚（NIPAAm-共-HPMAm-乳酸酯）的聚合物胶束的不稳定。
Diblock copolymers of poly(N-isopropylacrylamide-co-N-(2-hydroxypropyl)methacrylamide lactate) (poly(NIPAAm-co-HPMAm-lactate)) as a thermosensitive block and poly(ethylene glycol) (PEG) as a hydrophilic block form polymeric micelles above the cloud point (CP) of the temperature-sensitive block. Destabilization of these micelles occurs upon hydrolysis of the lactate side chains. Here we report on the degradation kinetics of the HPMAm-mono(di)lactate monomers and their copolymers with NIPAAm. The degradation of the monomers and polymers in their soluble state (thus below their CP) followed normal ester hydrolysis behavior: the degradation rate increased with temperature, pH (from pH 7.5 to 11), and dielectric constant of the medium. Above the CP, where the polymers are in a precipitated state, a significant retardation of the polymer degradation occurred due to a decrease of dielectric constant of the local environment of the precipitated polymer. This study shows that it is possible to predict the rate of formation of HPMAm in NIPAAm-co-HPAIAm-lactate copolymers which results in an increase of the overall hydrophilicity of the polymers and destabilization of polymeric micelles based on poly(NIPAAm-co-HPMAm-lactate).