Nucleation and crystallization of poly(L-lactide) assisted by terminal hydrogen-bonding segments
Nucleation and crystallization of poly(L-lactide) assisted by terminal hydrogen-bonding segments
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末端氢键链段辅助聚(L-丙交酯)的成核和结晶
DOI：
10.1016/j.polymer.2022.125031
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发表时间：
2022-06
期刊：
影响因子：
4.6
通讯作者：
Piming Ma
中科院分区：
文献类型：
--
作者：
Manman Yu;Youpei Du;Pengwu Xu;Weijun Yang;Pingxia Zhang;Tianxi Liu;Pieter Jan Lemstra;Piming Ma
氢键（H-键）在聚合物成核和结晶中的作用尚不清楚。为了理解这一物理问题，我们设计了一系列末端含有不同数量草酰胺链段（OXA，-NHCOCONH-）的聚L-丙交酯（PLLA）作为模型氢键聚合物（PLLAnOXA，n为-NHCO-的数目），并结合实验和分子动力学（MD）模拟研究了氢键对聚合物成核和结晶的影响.与PLLA相比，在PLLAnOXA体系中，OXA链段与PLLA链或其他OXA链段之间形成了更多类型的氢键。链段可以通过氢键诱导的拓扑约束和/或空间位阻固定在熔体中，导致一定程度的熵降低。因此，作为“第一茎”的前体的一对H键合的片段预期在升高的温度下诱导局部有序结构（LOS），这进一步促进初级核和次级核的形成。因此，nOXA链段诱导的氢键不仅显著提高了PLLA的结晶温度（Tc，从100 °C到112 °C）和结晶度（Xc，从10%到52%），而且还将晶体生长速率（G）提高了近10倍（在150 °C下从0.25到2.66 μm min− 1）。此外，在非等温（1 °C/min）和等温（135 °C）条件下，通过原位小角X射线散射（SAXS）揭示了PLLAnOX A熔体中的HI-MS（氢键诱导的多阶段）成核现象。HI-MS的成核机理与nOXA诱导的多种氢键在一定的高温下具有不同的结晶稳定性有关。因此，本工作不仅提供了一种新的路线，使快速结晶PLLA通过杂化氢键链段，但也提供了一个分子水平的洞察力，在氢键辅助成核的半结晶聚合物一般。
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 PLLAnOXAsystems. 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 °C to 112 °C) 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−1at 150 °C). Moreover, a HI-MS (H-bond induced multi-stage) nucleation phenomenon in the melt of the PLLAnOXAwas revealed by in-situ small-angle X-ray scattering (SAXS) under both non-isothermal (1 °C/min) and isothermal (135 °C) 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.
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