Tsuji Hideto, Eto Takehiko, Sakamoto Yuzuru
Department of Environmental and Life Sciences, Graduate School of Technology, Toyohashi University of Technology, Tempaku-cho, Toyohashi, Aichi 441-8580, Japan.
Materials (Basel). 2011 Aug 10;4(8):1384-1398. doi: 10.3390/ma4081384.
Non-substituted racemic poly(DL-lactic acid) (PLA) and substituted racemic poly(DL-lactic acid)s or poly(DL-2-hydroxyalkanoic acid)s with different side-chain lengths, i.e., poly(DL-2-hydroxybutanoic acid) (PBA), poly(DL-2-hydroxyhexanoic acid) (PHA), and poly(DL-2-hydroxydecanoic acid) (PDA) were synthesized by acid-catalyzed polycondensation of DL-lactic acid (LA), DL-2-hydroxybutanoic acid (BA), DL-2-hydroxyhexanoic acid (HA), and DL-2-hydroxydecanoic acid (DA), respectively. The hydrolytic degradation behavior was investigated in phosphate-buffered solution at 80 and 37 °C by gravimetry and gel permeation chromatography. It was found that the reactivity of monomers during polycondensation as monitored by the degree of polymerization (DP) decreased in the following order: LA > DA > BA > HA. The hydrolytic degradation rate traced by DP and weight loss at 80 °C decreased in the following order: PLA > PDA > PHA > PBA and that monitored by DP at 37 °C decreased in the following order: PLA > PDA > PBA > PHA. LA and PLA had the highest reactivity during polymerization and hydrolytic degradation rate, respectively, and were followed by DA and PDA. BA, HA, PBA, and PHA had the lowest reactivity during polymerization and hydrolytic degradation rate. The findings of the present study strongly suggest that inter-chain interactions play a major role in the reactivity of non-substituted and substituted LA monomers and degradation rate of the non-substituted and substituted PLA, along with steric hindrance of the side chains as can be expected.
通过分别对DL-乳酸（LA）、DL-2-羟基丁酸（BA）、DL-2-羟基己酸（HA）和DL-2-羟基癸酸（DA）进行酸催化缩聚反应，合成了未取代的外消旋聚（DL-乳酸）（PLA）以及具有不同侧链长度的取代外消旋聚（DL-乳酸）或聚（DL-2-羟基链烷酸），即聚（DL-2-羟基丁酸）（PBA）、聚（DL-2-羟基己酸）（PHA）和聚（DL-2-羟基癸酸）（PDA）。通过重量法和凝胶渗透色谱法研究了在80℃和37℃的磷酸盐缓冲溶液中的水解降解行为。结果发现，以聚合度（DP）监测的缩聚反应过程中单体的反应活性按以下顺序降低：LA＞DA＞BA＞HA。以DP和80℃下的重量损失追踪的水解降解速率按以下顺序降低：PLA＞PDA＞PHA＞PBA，而在37℃下以DP监测的水解降解速率按以下顺序降低：PLA＞PDA＞PBA＞PHA。LA和PLA分别在聚合反应和水解降解速率方面具有最高的反应活性，其次是DA和PDA。BA、HA、PBA和PHA在聚合反应和水解降解速率方面具有最低的反应活性。本研究结果强烈表明，链间相互作用在未取代和取代的LA单体的反应活性以及未取代和取代的PLA的降解速率中起主要作用，同时正如预期的那样，侧链的空间位阻也起作用。
