Selective branch formation in ethylene polymerization to access precise ethylene-propylene copolymers

Yuxing Zhang,Zhongbao Jian,Xiaohui Kang

doi:10.1038/s41467-022-28282-z

Abstract

Polyolefins with branches produced by ethylene alone via chain walking are highly desired in industry. Selective branch formation from uncontrolled chain walking is a long-standing challenge to generate exclusively branched polyolefins, however. Here we report such desirable microstructures in ethylene polymerization by using sterically constrained α-diimine nickel(II)/palladium(II) catalysts at 30 °C–90 °C that fall into industrial conditions. Branched polyethylenes with exclusive branch pattern of methyl branches (99%) and notably selective branch distribution of 1,4-Me2 unit (86%) can be generated. The ultrahigh degree of branching (>200 Me/1000 C) enables the well-defined product to mimic ethylene-propylene copolymers. More interestingly, branch distribution is predictable and computable by using a simple statistical model of p(1-p)n (p: the probability of branch formation). Mechanistic insights into the branch formation including branch pattern and branch distribution by an in-depth density functional theory (DFT) calculation are elucidated.

Highlights

Polyolefins with branches produced by ethylene alone via chain walking are highly desired in industry
In the ethylene/propylene (EP) copolymer, linear low-density polyethylene (LLDPE), and polyolefin elastomer (POE) products, branch on the backbone of PEs is originated from C3, C4, C6, or C8 α-olefins
We report that the low-cost nickel(II) catalyst shows a superior control on selective branch formation in ethylene polymerization, enabling the production of an exclusive methyl branch pattern with an ultrahigh number in a broad temperature range of 30–90 °C that meets the industrial process

Summary

Introduction

Polyolefins with branches produced by ethylene alone via chain walking are highly desired in industry. We report that the low-cost nickel(II) catalyst shows a superior control on selective branch formation in ethylene polymerization, enabling the production of an exclusive methyl branch pattern with an ultrahigh number in a broad temperature range of 30–90 °C that meets the industrial process.

Results

Conclusion