简介：为探究氢键在聚合物成核和结晶中的作用，本文设计了一系列具有不同数量末端草酰胺链段(OXA，-NHCOCONH-)的聚(L-丙交酯)(PLLA)作为模型氢键聚合物(PLLAnOXA，n是-NHCO-的数目)，然后通过实验和分子动力学模拟相结合的方法研究了氢键对聚合物成核和结晶的影响。本工作不仅提供了一种通过杂化氢键片段快速结晶PLLA的新方法，而且提供了一种在分子水平上研究氢键辅助半结晶聚合物成核的方法。
摘要：The role of hydrogen bonding (H-bonding) in polymer nucleation and crystallization is not yet so clear. To understand this physical issue, a series of poly (L-lactide) (PLLA) with different amount of terminal oxamide segments (OXA, -NHCOCONH-) were tailor-made as model H-bonding polymers (PLLAnOXA, n is the number of -NHCO-), and then the influence of H-bonding on the polymer nucleation and crystallization were investigated by a combination of experiments and molecular dynamics (MD) simulations. Compared with PLLA, much more types of H-bonds are created between the OXA segments and either the PLLA chains or the other OXA segments in the PLLAnOXA systems. A segment can be immobilized in the melt by H-bonding induced topological constraint and/or steric hindrance leading to a certain extent of reduction in entropy. Thus, the pair of H-bonded segments acting as a precursor of the “first stems” is expected to inducing local ordered structures (LOS) at elevated temperatures, which further facilitates the formation of both primary and secondary nuclei. As a consequence, the nOXA segments induced H-bonds not only significantly enhanced the crystallization temperature (Tc, from 100 ℃ to 112 ℃) and the crystallinity (Xc, from 10 % to 52 %) of PLLA, but also increases the crystal growth rate (G) by nearly 10 times (from 0.25 to 2.66 μm·min-1 at 150 ℃). Moreover, a HI-MS (H-bond induced multi-stage) nucleation phenomenon in the melt of the PLLAnOXA was revealed by in-situ small-angle X-ray scattering (SAXS) under both non-isothermal (1 ℃/min) and isothermal (135 ℃) conditions. The HI-MS nucleation mechanism is well correlated to the nOXA induced multi-types of H-bonds which possess different thermodynamical stability at a certain high temperature. Therefore, this work not only provides a new route to make rapid crystallizing PLLA via hybridizing H-bonding segments, but also provides a molecular-level insight in the H-bonding assisted nucleation of semi-crystalline polymers in general.
相关成果以标题为“Nucleation and Crystallization of Poly(L-lactide) Assisted by Terminal Hydrogen-Bonding Segments”发表于国际期刊Polymer上。
文章链接：https://doi.org/10.1016/j.polymer.2022.125031
