Toward all stereocomplex-type polylactide with outstanding melt stability and crystallizability via solid-state transesterification between enantiomeric poly(L-lactide) and poly(D-lactide)
Toward all stereocomplex-type polylactide with outstanding melt stability and crystallizability via solid-state transesterification between enantiomeric poly(L-lactide) and poly(D-lactide)
复制标题
通过对映体聚(L-丙交酯)和聚(D-丙交酯)之间的固态酯交换反应，获得具有优异熔融稳定性和结晶性的全立体络合物型聚丙交酯
DOI：
10.1016/j.polymer.2020.122850
复制
发表时间：
2020-09-28
期刊：
影响因子：
4.6
通讯作者：
Fu, Qiang
中科院分区：
文献类型：
--
作者：
Li, Xiangli;Yang, Dongsheng;Fu, Qiang
立体嵌段共聚被认为是大幅度提高高相对分子质量立体复合型聚乳酸熔体稳定性(即聚L-丙交酯(PLLA)和聚D-丙交酯(PDLA)熔融时分子间协作的生存能力)的一种有吸引力的策略，但它通常存在合成过程复杂甚至影响可持续性的问题。因此，固态酯交换反应(SST)被设计为一种简便而稳健的方法，可以从市售的线性高相对分子质量PLLA/PDLA(50/50)共混物中制备独特的多立体嵌段聚乳酸共聚物，具有优异的熔体稳定性和出人意料的强结晶性能。在微量(0.03-0.035%)催化剂存在下，聚乳酸和聚乳酸通过低温(即180℃)熔融共混，聚乳酸对映体链熔融后可以迅速共晶成固态SC微晶，随后Hetem链的酯交换反应只在预制得SC微晶的可移动无定形相中进行。结果，原位生成了具有长可结晶PLLA和PDLA嵌段的多嵌段PLLA-b-PDLLA-b-PDLA共聚物。结果表明，即使在较高的冷却速度(例如，40℃/分钟)和较低的温度(例如，140℃)下，共聚物的熔融结晶过程中也可以完全形成高含量的Sc微晶。更有趣的是，不可结晶的PDLLA嵌段的存在不仅不会干扰对映体聚乳酸嵌段的SC结晶能力，如PLLA/PDLA共混物的高结晶度和熔融温度所证明的那样，而且还通过稳定共聚熔体中有序的PLLA/PDLA链段簇来提高结晶速度。总体而言，这些发现可能为开发可熔融加工的全SC-聚乳酸工程应用开辟一条新的途径。
Stereoblock copolymerization is regarded an appealing strategy to substantially enhance the melt stability (i.e., the survival ability of the intermolecular collaboration between poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) upon melting) of high-molecular-weight (high-MW) stereocomplex-type polylactide (SC-PLA), however it usually suffers from complicated synthetic procedures and even impaired sustainability. Herein, solid-state transesterification (SST) has been devised as a facile and robust route to prepare unique multi-stereoblock PLA copolymers with outstanding melt stability and unexpectedly strong crystallizability from commercial available linear high-MW PLLA/PDLA (50/50) blends. The SST was performed through low-temperature (i.e., 180 degrees C) melt-blending of PLLA and PDLA in the presence of trace amounts (0.03-0.035 wt%) of catalysts, where the enantiomeric PLA chains could rapidly co-crystallize into solid-state SC crystallites upon melting and subsequently the hetem-chain transesterification reaction occurs exclusively in the mobile amorphous phase of the pre-formed SC crystallites. As a result, multiblock-like PLLA-b-PDLLA-b-PDLA copolymers with long crystallizable PLLA and PDLA blocks are in-situ generated. The results show that high-content SC crystallites can be exclusively formed in the melt-crystallization of the copolymers even at high cooling rates (e.g., 40 degrees C/min) and low temperatures (e.g., 140 degrees C). More interestingly, the presence of the non-crystallizable PDLLA blocks not only does not disturb the SC crystallizability of the enantiomeric PLA blocks, as evidenced by the same high crystallinity and melting temperature as those of starting PLLA/PDLA blends, but also increase the crystallization rate by stabilizing the clusters of ordered PLLA/PDLA segments in the copolymer melt. Overall, these findings could open a new pathway to develop melt-processible all SC-PLA for engineering applications.