负载型催化剂活性点位设计与超高分子量聚乙烯微观结构的调控

Active-site position regulation is a difficult topic for the design of supported catalysts used in olefin polymerization and is one of the key factors that influence catalyst performance and product properties. In this application, polyhedral oligomeric silsesquioxanes (POSS), which has a molecular size of 1-3 nm, is to be used as a space isolator to occupy the immobilization points on the surface of catalyst carrier (silica). As a result, the POSS becomes the new combination point for active sites and a new supported catalyst with nano-particle isolators will be prepared, which can be used to prepare ultrahigh molecular weight polyethylene (UHMWPE). By changing the geometry, size and chemical composition of the POSS molecule, the distance between active sites can be adjusted, thus the suitable environment for chain growing built-up. In this way, the entanglement degree of the macromolecule chains can be modulated, so as to produce UHMWPE with super-high modulus and strength effectively during the gas-phase polymerization. In addition, high attention will be paid to the construction mechanism of the immobilization micro-environments on supported catalyst with nano-isolators, the coupling mechanism of chain growing and chain crystallizing processes, and chain entanglement formation mechanism during the gas-phase polymerization process, so as to reveal the relationship between UHMWPE chain generative character and catalyst micro-environments. Finally, a comprehensive model about process-structure- performance of UHMWPE will be established in order to quantitative regulation of the entanglement state in nascent UHMWPE particle. The success of this active-site position design theory on supported catalyst will contribute to the development of polymer reaction engineering in micro-scale field.

活性点位调控是负载型烯烃聚合催化剂设计的难点，也是决定催化剂特性和产品性质的关键因素之一。本申请拟采用尺寸为1-3 nm的多面齐聚倍半硅氧烷（POSS）为空间隔离物预先与"骨架"载体（硅胶）结合，占据硅胶的表面负载位，使其成为活性中心新的锚钉点，制备带纳米分子隔离的负载型超高分子量聚乙烯（UHMWPE）催化剂。通过改变POSS分子空间结构和化学组成，调节活性位间距，进而构建与活性中心特性相宜的链段生长环境，在气相聚合中调节UHMWPE链缠绕程度，高效地制备超强高模UHMWPE。重点研究带纳米分子隔离的负载微环境的构建机理、气相聚合中链增长和链段结晶过程的耦合机制及链缠绕形成机理，揭示纳微尺度下UHMWPE链段衍生特征与微观环境的关系，建立聚集态结构与产品性质构效关系模型，实现对UHMWPE链缠绕结构的有效控制。负载型催化剂活性点位设计理论的成功，将推动聚合反应工程在微尺度方面的更深入研究。

本项目以带纳米POSS分子隔离的负载型UHMWPE催化剂催化乙烯聚合为研究对象，利用POSS分子物理化学结构可调的性质，构建与活性中心特性相宜的链段生长环境，获得高度解缠绕结构的UHMWPE初生颗粒。并在保持催化剂具有高活性的前提下，研究了聚合中链增长过程和结晶过程的耦合作用、链缠绕的形成机理和微观环境下催化剂聚合机理，聚合物聚集态结构与产品性质构效关系。围绕无（低）缠结UHMWPE的制备工艺主要开展了以下工作：(1) POSS物理化学环境对催化剂负载方式、聚合机理的影响；（2）带POSS分子隔离的非均相催化剂的构建及其乙烯聚合行为；（3）聚合过程中聚合物链增长行为和结晶行为的耦合作用；（4）非均相聚合中聚乙烯链缠绕结构衍生机理；（5）无（低）缠结UHMWPE聚集态结构与性能表征。