Product Development Department, N.V. Organon, P.O. Box 20, 5340 BH Oss, The Netherlands.
Biomacromolecules. 2010 Apr 12;11(4):1118-24. doi: 10.1021/bm100125b.
The autocatalytic equation derived in this study describes and even predicts the evolution of the number average molecular weight of aliphatic polyesters upon hydrolytic degradation. The main reaction in the degradation of aliphatic polyesters is autocatalytic hydrolysis of ester bonds, which causes the molecular weight to decrease. During hydrolysis of the ester bonds in the main chain of the polyester, the chains are cleaved and the end group concentrations will rise. The fundamentals of this equation are based on that principle. To validate the derived equation, the hydrolytic degradation of poly(4-methylcaprolactone), poly(epsilon-caprolactone), poly(d,l-lactide), and two different poly(d,l-lactide-co-glycolide) copolymers was monitored after immersion in a PBS buffer (pH = 7.4) at 37 degrees C. The number average molecular weight, mass loss, and crystallinity were determined after different time intervals. The experimental results confirm that hydrolytic degradation of aliphatic polyesters is a bulk erosion process. When comparing the M(n), calculated with the new autocatalytic equation, with the experimental results, it was found that the new model can predict the decrease of the M(n) upon hydrolytic degradation for semicrystalline and amorphous polymers, as well as for copolymers, without the need for complicated mathematics and excessive input parameters. This is a major improvement with respect to earlier proposed models in literature.
本研究推导出的自动催化方程描述并预测了脂肪族聚酯在水解降解过程中数均分子量的演变。脂肪族聚酯降解的主要反应是酯键的自动催化水解，导致分子量下降。在聚酯主链中酯键的水解过程中，链被切断，端基浓度会上升。该方程的基础原理基于这一原则。为了验证推导的方程，将聚(4-甲基己内酯)、聚(ε-己内酯)、聚(D,L-丙交酯)和两种不同的聚(D,L-丙交酯-共-乙交酯)共聚物在 37°C 的 PBS 缓冲液(pH = 7.4)中浸泡后监测其水解降解。在不同的时间间隔后，测定数均分子量、质量损失和结晶度。实验结果证实，脂肪族聚酯的水解降解是一个整体侵蚀过程。将新的自动催化方程计算得到的 M(n)与实验结果进行比较，发现新模型可以预测半结晶和无定形聚合物以及共聚物在水解降解过程中 M(n)的下降，而无需复杂的数学和过多的输入参数。与文献中提出的早期模型相比，这是一个重大改进。
