基于高分子链限域溶胀行为的聚合微环境构建与聚乙烯链缠结调控

Ultrahigh molecular weight polyethylene with less entangled state can significantly decrease the molten viscosity, crystal defects and improve the property of final use. It is essential for synthesizing high-performance polyethylene products. In this project, polystyrene copolymers are incorporated into the pores of inorganic support through styrene in-situ free-radical copolymerization to develop hybrid support. This hybrid support will present a substantial transfer resistance to ethylene, and separate active sites into reacted micro-units based on the swelling behavior of polystyrene copolymers inside the confined pores. A suitably reacted micro-environment will be built up for hindering the chain overlap behavior during the ethylene polymerization. We aim at synthesizing the disentangled polyethylene with high activity, a stable entanglement density at a high temperature (≥ 60 ℃). The microstructure of hybrid support will be designed through the styrene in-situ free-radical copolymerization inside the confined pores. The transfer resistance to the ethylene of hybrid support, the polymerization mechanism based on the diffusion control of ethylene, and the evolution of the entangled state of nascent polymers will be studied quantitatively. Finally, synergistic effects of monomer diffusion, ethylene polymerization and chain crystallization to the polymerization behavior of catalyst, and the evolution of disentangled state will be discussed. This project will promote the development of the designation of heterogeneous catalyst for the olefin polymerization. It can support the development of polymer reaction engineering and product engineering at the micro scale.

降低初生态超高分子量聚乙烯的链缠结程度能够大幅降低熔体粘度和晶格缺陷，提升材料加工和使用性能，是聚烯烃高性能化的重要发展方向。本申请从负载型烯烃聚合催化剂聚合微环境的设计出发，通过在多孔无机载体孔道内进行的苯乙烯原位共聚，将带有负载官能团的苯乙烯共聚物植入孔道。充分利用受限孔道内苯乙烯共聚物的“限域溶胀”行为，结合乙烯传质阻力和催化剂颗粒破碎行为的调控，构建稳定的聚合微环境，抑制聚乙烯链交叠的发生。开发高温（≥ 60 ℃）、高效制备缠结程度稳定的低缠结超高分子量聚乙烯的聚合方法。重点研究负载型催化剂聚合微环境的构建机制，微环境下的催化剂聚合机理、初生态聚乙烯链缠结的表征方法和形成机制、以及熔体加工过程中链缠结的演变规律。深入理解烯烃聚合过程中单体传质-聚合反应-链段结晶的协同效应，完善非均相催化剂的设计方法，推动聚合反应工程和聚烯烃产品工程在纳微尺度上的更深入研究。

超高分子量聚乙烯（UHMWPE）初生颗粒内大量的链缠结不但使得产品熔体粘度大，加工性能差，也影响了产品力学性能的提升，始终制约着UHMWPE高性能化的发展。本申请从负载型催化剂聚合微环境的设计出发，通过在多孔无机载体孔道内进行的苯乙烯原位共聚，将聚苯乙烯植入孔道中。采用梯度场核磁共振技术和溶胀DSC方法研究了受限孔道内聚苯乙烯的限域溶胀行为，发现了良溶剂甲苯中聚苯乙烯的传质控制效应和不良溶剂庚烷中聚苯乙烯对活性中心的分隔效应与初生态UHMWPE链缠结结构的关系，提出了实现活性中心周围传质阻力和活性中心空间分布调控的负载型催化剂的制备方法。首次在60℃以上的工业聚合反应温度下，以极高的活性，平稳地制备低缠结UHMWPE。率先提出将聚乙烯初始储能模量和聚合活性组成坐标系，研究了温度、压力、时间等工艺条件对分子链结构和链缠结的影响，揭示了聚合过程中聚乙烯链缠结结构的演变规律，指导了UHMWPE产品设计。采用退火DSC、熔体流变和固体核磁共振技术研究了加工过程中链缠结的重建规律，发现低缠结UHMWPE具有更快的链段运动行为，能够在5min内烧结成型，与现有商业UHMWPE相比，成型时间缩短6倍。成型后，低缠结UHMWPE缺陷更少，能够实现刚性、韧性和强度的同步提升，尤其是冲击强度可达到110kJ/m2。基于上述认识，项目组先后完成10L、300L和6.8m3的工业放大聚合实验，聚合结果表明，催化剂活性高（20000 gPE/gCat）、活性释放稳定（6h）、产品分子量可调范围宽（120-760 万g/mol）、堆密度高、能够满足工业装置稳定生产的要求。最后，在下游生产企业成功开发了高强纤维、高流动性UHMWPE母粒等新产品，产品加工和力学性能全面超过进口产品。