PLA-乙二酰胺杂化大分子自成核及分子链结晶的协同诱导机制

Crystallization rate, physical properties and application range of poly (lactic acid) (PLA) are seriously restricted due to the large size and low efficiency of its nuclei. To solve these issues, PLA-based hybrid macromolecules with oxalamide segments in main chain are going to be designed and synthesized, and nano-sized nucleator is expected by molecular structure design and H-bonds assembly of oxalamide segments, then a novel idea on self-nucleation of macromolecules is raised. The effect of the amount, position and segmental structure of the H-bond units and the length of the PLA segments on the construction rate, size and lattice parameter of the nuclei will be systematically investigated. As a consequence, the method, theory and optimal hybrid structure for construction of the intramolecular nano-nucleator will be set up, and the corresponding construction mechanism will be illuminated based on the experimental data and dynamic model. The new packaging phenomena of the PLA chains induced by the nano-crystal nucleus and interfacial covalent bonds will be studied, and the synergetic effect of the interfacial covalent bonds on the crystallization behavior of the PLA chains will be analyzed as well. Finally, taking film as an example, biodegradable materials with transparency, heat-resistance and gas barrier properties will be made via crystallization and microstructure control. This work will not only enrich the traditional nucleation and crystallization theory, but also provide platform approach to super-thin crystal nuclei. Moreover, it would provide theoretical support for the preparation and property control of high-quality biodegradable materials.

聚乳酸（PLA）现有成核剂尺寸大、成核效率低，严重制约了其结晶速率、物理性能和应用领域。鉴于此，本研究拟从分子水平设计合成系列主链含有乙二酰胺链段的PLA杂化大分子，通过分子设计和氢键链段定向组装构筑纳米晶核，提出大分子自身异相成核的新思想。系统研究杂化大分子中氢键基团的数目、位置、链段结构和PLA链段长度等对晶核构筑的速度、尺度以及晶格参数的影响规律，建立杂化大分子诱导纳米晶核构筑的方法、理论及最佳杂化结构，结合实验数据与动力学模型阐明纳米晶核可控构筑的机理；深入研究纳米晶核与界面共价键协同诱导PLA分子链堆砌生长的新规律，剖析界面共价键对PLA分子链结晶行为的特殊作用机制；最后，通过成核与晶体结构调控制备透明、耐热且气体阻隔性能优异的可降解膜材料。本研究不仅将丰富传统成核与结晶理论，还将为超细晶核的可控构筑提供普适性技术路线、为高性能生物可降解材料的制备与性能调控提供重要的理论支撑。

聚乳酸是一种生物基与生物降解聚酯材料，但成核效率低、结晶速率慢、耐热性差等科学技术问题严重制约了其应用。针对该问题，本研究在小分子成核剂的研究基础上，设计合成了系列主链含有乙二酰胺链段的PLA杂化大分子，提出了大分子自身异相成核的新概念。系统研究了杂化大分子中氢键基团的数目、位置、结构、分子链柔顺性、氢键单元与PLA链段之间链接等因素对PLA成核及结晶行为的影响规律，确定了最佳杂化结构；显著提高了PLA的结晶度、结晶速率和耐热性，同时赋予PLA更优异的透明性，建立了氢键辅助的聚乳酸快速成核结晶的新方法、新理论和新模型；通过分子动力学模拟揭示了分子内与分子间氢键作用对聚乳酸成核诱导期、二次成核及晶体生长过程的影响规律，以及氢键促进成核的作用机制。本研究不仅丰富了传统成核与结晶理论，而且为自身快速成核结晶的聚合物可控构筑提供了理论指导、为高品质生物可降解材料的制备与性能调控提供重要的技术支撑。