A Systematic Study of the Temperature-Induced Performance Decline of ansa-Metallocenes for iPP

Highly accurate high-throughput experimentation (HTE) data for a set of 21 silicon-bridged C2-symmetric ansa-zirconocenes in propene homopolymerization were collected and were used to develop quantitative structure – activity relationship (QSAR) models for several performance indicators at high polymerization temperature (Tp = 100 °C) by using chemically meaningful descriptors. Most notably, stereoselectivity is well described by a two-descriptor model linking the quadrant model for stereoselectivity (sterics) with the chain epimerization model (electronics). The catalysts show widely varying temperature responses, most notably on stereoselectivity and molar mass capability, while the regioselectivity response is uniformly weak. Soft conformational locks lose their performance rapidly while hard conformational locks offer enhanced performance even at high temperatures. The quest for high-temperature stable, well-performing ansa-zirconocenes will unquestionably lead to systems with enhanced rigidity.本研究采集了21种硅桥联C₂对称ansa-锆茂金属（ansa-zirconocenes）在丙烯均聚反应中的高精度高通量实验（high-throughput experimentation, HTE）数据，并基于具有化学意义的描述符，针对高温聚合条件（Tp=100℃）下的多项性能指标构建了定量构效关系（quantitative structure-activity relationship, QSAR）模型。尤为关键的是，立体选择性可通过双描述符模型得到良好拟合，该模型将立体选择性的象限模型（空间位阻因素）与链异构化模型（电子效应因素）相结合。此类催化剂展现出差异显著的温度响应特性，尤以立体选择性与摩尔质量调控能力最为突出，而区域选择性的温度响应则普遍较弱。柔性构象锁的催化性能会随温度升高快速衰减，而刚性构象锁即便在高温条件下仍可保持优异的催化性能。开发高温稳定且性能优异的ansa-锆茂金属催化剂，无疑将指向具有更高刚性的分子体系。