界面动力学加速聚（l-丙交酯）嵌段聚合物塑料的老化，同时保持韧性

摘要(中文译文)

聚乳酸（PLA）均聚物在熔融加工后两天内会因物理老化而在环境条件下变脆，这限制了其作为石油基不可降解塑料的可持续替代品的发展。含有PLA和不相容橡胶态链段的嵌段聚合物已显示出良好的机械耐久性，但仅在总摩尔质量非常高的情况下才能实现。为阐明此类抗老化材料的基本结构特征和形态特征，我们采用简便的两步合成路线制备了一系列n臂嵌段聚合物塑料（n=1-4），以聚（γ-甲基-ε-己内酯）（PγMCL）为橡胶态核心，以聚（L-丙交酯）（PLLA）为外层嵌段，并将PLLA含量固定为80 wt%。三嵌段和星形嵌段（即n≥2）表现出高拉伸韧性，且即使在PLLA基体缠结不良的样品中，这种韧性也能在长时间老化后得以保持。结晶度和结构纯度也有助于提高机械耐久性。量热分析表明，n<35 kg mol的最具机械耐久性的样品表现出最快的物理老化，我们将其归因于分离的PγMCL域界面附近嵌段动力学的耦合作用。我们的结果将PLLA机械耐久性的可行嵌段聚合物结构范围拓展至更易合成的大分子，这些大分子在可扩展性和熔融加工方面具有实际优势。

Abstract

Poly-(lactide) (PLA) homopolymer embrittles under ambient conditions within two days after melt processing through physical aging, which restricts its growth as a sustainable alternative to petroleum-derived, nondegradable plastics. Block polymers containing PLA and immiscible rubbery segments have shown promising mechanical longevity, though only at very high total molar masses. To elucidate the basic architectural and morphological features of such aging-resistant materials, we used a straightforward two-step synthetic route to generate a library of -arm block polymer plastics ( = 1-4) with poly-(γ-methyl-ε-caprolactone) (PγMCL) as the rubbery core and poly-(l-lactide) (PLLA) as the outer block, fixing PLLA content at 80 wt %. Triblocks and star-blocks (i.e., ≥ 2) exhibited high tensile toughness that persisted over long aging times even in samples with poorly entangled PLLA matrices. Crystallinity and architectural purity also promoted mechanical longevity. Calorimetry revealed that the most mechanically long-lived specimens, with < 35 kg mol, exhibited the fastest physical aging, which we ascribed to a coupling of block dynamics near the segregated PγMCL domain interfaces. Our results broaden the scope of viable block polymer architectures for PLLA mechanical longevity to more synthetically accessible macromolecules that are practically advantageous for scalability and melt processing.

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