高分子体系聚合诱导自组装结构及其形成机理

Self-assembly of block copolymers is an important route for preparing nanomaterials. However, conventional self-assembly technology of block copolymers is technically complicated and encounters difficulties in the preparation of large amount of materials in scale-up industry production. In recent years, a new design strategy, as called polymerization-induced self-assembly (PISA), is proposed to cover the shortage of conventional self-assembly technology. In PISA process, polymerization and self-assembly of block copolymer take place simultaneously. The polymerization is the driving force of self-assembly. Limited by the characterization measurements in experiment, now it is far from well understanding of the PISA process. In this project, we mean to use multiscale computer simulation method to study the controlling factors in PISA. Firstly, based on the coarse-grained stochastic polymerization method developed by the applicant, we plan to construct the PISA simulation model to study the cooperation/competition mechanism between the polymerization and self-assembly. As the driving force of self-assembly, the contribution of polymerization on PISA process will be clarified. The influence of monomer feed ratio and the fraction of macromolecular initiator on the morphology of aggregations will also be discovered. Furthermore, experimental studies will be carried out on specific PISA systems, to validate the systematic results obtained from computer simulations. The experimental conditions and designing rules, which are beneficial to the preparation of self-assembly structures with large size and low defect, will be proposed. This project will provide reliable guideline for the design of optimized polymer self-assembly materials in laboratories as well as in industry.

嵌段共聚物的自组装是制备纳米材料的重要手段，然而传统的自组装工艺流程复杂且不容易工业化生产。近年来提出的聚合诱导自组装（PISA）的设计思路可弥补传统自组装工艺的不足。在PISA中聚合反应与嵌段共聚物的自组装协同发生，而聚合反应则是自组装的驱动力。受实验表征手段的限制，目前对PISA过程的认识很不完善。本项目拟发展并利用多尺度计算机模拟方法，研究PISA中影响自组装结构的主控因素。首先基于申请人已开发的粗粒化随机聚合反应方法构建PISA体系的模型，研究聚合反应与自组装的协同/竞争机制，明晰聚合反应驱动力对自组装的贡献，以及单体投料比、链引发剂的比例等因素对自组装结构的影响规律。进一步针对典型的PISA体系开展实验研究，对模拟所得到的规律性结果进行实验验证，从而总结有利于制备大尺寸、少缺陷的自组装结构的实验条件和规律。为实验室和工业上定向设计优异的聚合物自组装材料提供指导。

本项目通过多尺度计算机模拟方法，研究了聚合诱导自组装PISA过程中影响产物结构的主控因素。成功开发了聚合诱导自组装的粗粒化动力学模型，并对其形貌及自组装的热力学和动力学机理进行了深入探讨。模拟研究发现通过调控亲溶剂嵌段和疏溶剂嵌段的比例，可以有效地调控PISA过程所产生的自组装形貌。计算机模拟研究发现，在快速链增长的PISA自组装过程中，疏溶剂嵌段和亲溶剂嵌段经历了一个特殊的结构翻转，从而形成最终的囊泡结构。. 聚合诱导协同组装PICA是上述PISA体系的一个典型应用。PICA通过在PISA中加入小分子链转移剂，实现疏溶剂均聚物的链增长反应来调控体系的高级形貌。模拟研究发现，疏溶剂均聚物的存在会产生“阻链生长效应”，从而有效地减缓聚合反应动力学过程。模拟结果验证了均聚物首先达到溶解度极限形成疏溶剂核，从而诱导嵌段共聚物吸附的动力学机制。除了在实验中已观察到的低阶形貌向高阶形貌的转变外，模拟研究还发现了特殊的高阶形貌向低阶形貌的转变，这是系统自适应行为的结果。通过扫描参数空间，模拟进一步构建了PICA体系的形貌相图。. 基于前期关于PISA和PICA的研究基础，进一步探究了实验工艺手段所带来的聚合物分子量分布的影响。模拟研究分别探究了匀速和分步滴加大分子链转移剂对聚合物的分子量分布、尺寸以及动力学转变路径的影响。模拟结果表明，使用分步滴加大分子链转移剂的方法可以实现对聚集体尺寸的精确调控，初始加入的大分子链转移剂与疏水单体聚合形成较长的嵌段并充当骨架，使形成的囊泡空腔变大，聚集体的尺寸随之增大。此外模拟研究发现了形成囊泡的新路径，即体系在早期先形成一个小囊泡，接下来形成的嵌段在自组装的过程中不断使小囊泡变大。. 该模型的开发和研究方法的构建为理解聚合诱导自组装过程形貌调控的因素提供了理论帮助，同时对改进实验工艺有一定的指导作用。该项目的系统研究对实验上制备更加丰富的PISA形貌具有指导意义。