Data for Crystallinity-independent toughness in renewable poly(L-lactide) triblock plastics

Poly(L-lactide) (PLLA)’s broad applicability is hindered by its brittleness and slow crystallization kinetics. Among the strategies for developing tough, thermally resilient PLLA-based materials, the utilization of neat PLLA block polymers has received comparatively little attention despite its attractive technological merits. In this work, we comprehensively describe the microstructural, thermal, and mechanical properties of two compositional libraries of PLLA-rich PLLA-b-poly(γ-methyl-ε-caprolactone) (PγMCL)-b-PLLA (“LML”) triblock copolymers. The rubbery PγMCL domains microphase separate from the matrix in the melt and intercalate between PLLA crystal lamellae on cooling. Despite the mobility constraints associated with mid-block tethering, the PLLA end-blocks crystallize as rapidly as a PLLA homopolymer control of similar molar mass. Independent of their degree of crystallinity, LML triblocks exhibit vastly improved tensile toughnesses (63-113 MJ m-3) over that of PLLA homopolymer (1.3-2 MJ m-3), with crystallinities of up to 55% and heat distortion temperatures (HDTs) as high as 148 °C. We investigated the microstructural origins of this appealing performance using X-ray scattering and microscopy. In the case of a largely amorphous PLLA matrix, the PγMCL domains cavitate to enable concurrent PLLA shear yielding and strain-induced crystallization. In highly crystalline PLLA matrices, PγMCL facilitates a lamellar-to-fibrillar transition during tensile deformation, the first such transition reported for PLLA drawn at room temperature. These results highlight the unique attributes of PLLA block polymers and prompt future architectural and processing optimizations to achieve ultratough, high-HDT PLLA block polymer plastics after a simple thermal history on economical timescales.

聚左旋乳酸(Poly(L-lactide))因其脆性与缓慢的结晶动力学特性，应用范围受到显著限制。在开发高韧性、耐热形变的PLLA基材料的诸多策略中，纯PLLA嵌段聚合物的应用虽具备诱人的技术优势，却未得到足够关注。本研究全面表征了两类组成库的富PLLA型PLLA-b-聚(γ-甲基-ε-己内酯)(PγMCL)-b-PLLA（简称LML）三嵌段共聚物的微观结构、热学与力学性能。弹性PγMCL畴区在熔融态下会与基体发生微相分离，并在降温过程中插层进入PLLA晶体片晶之间。尽管中间嵌段锚定作用会带来分子链迁移限制，PLLA端嵌段的结晶速率仍可与摩尔质量相近的纯PLLA均聚物对照样相当。无论结晶度高低，LML三嵌段共聚物的拉伸韧性（63~113 MJ·m⁻³）均远优于纯PLLA均聚物（1.3~2 MJ·m⁻³），其最高结晶度可达55%，热变形温度(HDT)最高可达148 ℃。本研究通过X射线散射与显微成像技术，探究了该优异性能的微观结构起源。在基体基本为无定形结构的样品中，PγMCL畴区发生空化作用，可同步实现PLLA的剪切屈服与应变诱导结晶；在高结晶度PLLA基体中，PγMCL可促进拉伸变形过程中片晶-原纤转变——这是室温拉伸PLLA时首次报道的此类转变。本研究结果凸显了PLLA嵌段聚合物的独特优势，并为后续通过优化分子结构与加工工艺，在经济可行的时间尺度内经过简单热历史处理即可制备超韧、高HDT的PLLA嵌段聚合物塑料提供了指引。