少量环状结构单元对新型丁烯共聚物结晶和相转变的影响

Copolymerization is an effective approach to control the crystalline structures and properties of butene based polymers. It was recently found that the structural unit of five-carbon ring type introduced into the main chain can effectively accelerate phase transition from tetragonal form II to hexagonal form I and even induces direct formation of the thermodynamically stable hexagonal modification. This proposal will utilize highly selective catalysts to vary ring-type structural units to obtain novel butene copolymers. Based on these new macromolecular structures, we aim at elucidating the role of copolymerized structures in phase transition, quantifying dependence of acceleration effect on concentration of copolymerized units, and revealing the mechanism of phase transition. Considering the fact that the intrinsic crystallization behavior is varied in copolymers, we will further investigate the relationship between memory effect appearance and molecular structures, reveal their resulting influences on crystallization kinetics and polymorphism, explore flow-induced crystallization behaviors as well as the coupling effect of flow with memory effect. This proposal expects to establish the working strategy including tailoring of macromolecular structure by chemical copolymerization, revealing physical mechanism of phase transition and memory effect, and fundamental understanding of processing-relevant flow-induced crystallization, in order to provide theoretical support for innovation of butene copolymer.

共聚是调控等规聚丁烯材料晶态结构和性能的一个重要方法。前期研究发现，主链中引入环状结构单元可以显著加速II-I相转变动力学，甚至诱导热力学稳定相的直接形成。本项目拟利用高选择性催化剂，设计合成含有不同环状结构单元的新型大分子，确定促进相转变的共聚结构，量化转变加速效应与环状结构单元含量的关系，获得结构明确的新型丁烯共聚物，揭示相转变机理。针对共聚物本征结晶行为，阐明记忆效应对共聚结构的依赖性，明确对结晶动力学和多晶型特性的作用，探索新型共聚物的流动诱导结晶行为，以及流动场与记忆效应的耦合。本项目期望建立从大分子结构的化学合成出发，包括相转变和记忆效应的物理机理，以及加工相关流动诱导结晶的系统工作思路，为新型聚丁烯材料的开发提供理论支撑。

丁烯基聚合物是一类具有优异力学性质的聚烯烃材料，通过共聚引入少量结构单元是有效改变分子链化学结构来调控物理晶态结构及性能的重要方法。本项目从分子链设计合成出发，利用高活性、高选择性铪催化剂体系和锆催化剂体系等，成功制备多个系列共聚单元结构明确、插入率可调的新型含环状结构单元丁烯基共聚物，详细研究共聚单元结构和插入率对聚合物结晶和相转变、记忆效应以及流动诱导结晶行为的影响。共聚物中引入降冰片烯和亚甲基-1,3-环戊烷共聚单元，均可显著加速具有动力学优势的四方相form II向热力学稳定的三方相form I固态晶型转变，还可结合较高结晶温度诱导无定形熔体直接生成三方相form I′，为获得稳定相提供了直接路径。1,6-庚二烯、环己烯、乙烯基环戊烷、乙烯基环己烷和4-(3-丁烯基)甲苯等多种环状共聚单元则可稳定四方相form II，有效调节晶态结构稳定性。其次，环状结构单元可诱导共聚物产生记忆效应，利用系列含五元、六元环结构单元的共聚物模型体系，详细研究熔融记忆效应与共聚单元含量定量关系，明确了诱导共聚物平衡熔点以上记忆效应的临界无定形含量标准。设计合成了存在分子间弱相互作用的含环状结构单元共聚物，通过诱导相分离增强记忆效应强度。同时，流动场会改变不同晶型之间的动力学优势。基于含亚甲基-1,3-环戊烯单元共聚物，发现流动场能同时加速三方相form I′和四方相form II结晶，而后者具有更强应变依赖性，即增加流动场更利于四方相form II晶体生成，构建了其流动场诱导结晶相图，为共聚物分子结构设计和加工流动场参数选择提供了研究基础。