University of the Basque Country (UPV/EHU), Department of Mining-Metallurgy Engineering and Materials Science, School of Engineering, Alameda de Urquijo s/n. 48013 Bilbao, Spain.
J Mech Behav Biomed Mater. 2012 Aug;12:29-38. doi: 10.1016/j.jmbbm.2012.03.008. Epub 2012 Mar 24.
Three statistical poly(L-lactide-co-ε-caprolactone) (PLCL) copolymers of 70% L-lactide content having different chain microstructures ranging from moderate blocky to random (R=0.47,0.69 and 0.92, respectively) were characterized by DSC, GPC and (1)H and (13)C NMR. The results demonstrate that higher randomness character (R→1) limits the capability of crystallization of LA-unit sequences shifting the melting temperature of the copolymers to lower values and reducing the crystallinity fraction substantially. The effect of different distributions of sequences of PLCL on crystallization and phase behavior was also studied for different storage times at room temperature (21±2°C) by DSC. The mechanical properties were evaluated by tensile tests during aging. The PLCL showing a random character closest to the Bernoullian distribution of sequences (l(LA)=1/CL) was found to exhibit higher strain capability and strain recovery values and is less prone to supramolecular arrangements. However, as a result of aging, L-lactide sequence blocks in the other PLCLs of smaller randomness character tend to crystallize prompting to a double T(g) behavior indicative of the existence of phase separation into two compositionally different amorphous phases. Physical aging leads also to dramatic changes in tensile behavior of the moderate blocky PLCLs that evolved from being an elastomeric to be partly a glassy semicrystalline thermoplastic, and, thus, can eventually condition its potential uses for medical devices.
三种统计聚（L-丙交酯-co-ε-己内酯）（PLCL）共聚物，其 L-丙交酯含量为 70%，具有不同的链微观结构，从中等嵌段到无规（R 分别为 0.47、0.69 和 0.92），通过 DSC、GPC 和（1）H 和（13）C NMR 进行了表征。结果表明，更高的无规性特征（R→1）限制了 LA-单元序列的结晶能力，使共聚物的熔点降低，并大大降低了结晶度分数。还通过 DSC 研究了不同序列分布的 PLCL 对结晶和相行为的影响，在室温（21±2°C）下不同的储存时间。通过拉伸试验在老化过程中评估了力学性能。发现具有最接近序列伯努利分布（l（LA）=1/CL）的无规特征的 PLCL 表现出更高的应变能力和应变恢复值，并且不易发生超分子排列。然而，由于老化，较小无规性特征的其他 PLCL 中的 L-丙交酯序列块倾向于结晶，促使出现双 T（g）行为，表明存在相分离成两个组成不同的非晶相。物理老化还导致中等嵌段 PLCL 的拉伸行为发生剧烈变化，从弹性体演变为部分玻璃态半结晶热塑性体，从而可能限制其在医疗器械中的潜在用途。
