Tailoring chain structures in Ethylene/Propylene copolymers through controlled monomer feeding strategies

Abstract

Polyolefins with desired properties can be achieved through precise control of chain structure. This study emphasizes the critical role of monomer feeding strategies in determining chain sequence distribution and topology to enhance the performance of ethylene/propylene rubbers (EPMs). Linear EPMs were synthesized via continuously feeding a fixed composition ethylene/ propylene mixture or through sequential monomer feeding. In contract, long-chain branched (LCB) EPMs (B-EPs) were produced via a tandem catalytic polymerization process, in which macromonomers were first synthesized and subsequently copolymerized with a continuous feed of ethylene/ propylene mixture with fixed composition. The impact of these feeding strategies on the resulting polymer chain structures, as well as their mechanical, thermal, and rheological properties, were systematically investigated. Incorporating 0.7 isotactic polypropylene (iPP) LCBs into the EPM backbone significantly improved the B-EP properties, yielding a high melting point of 141 °C and a low-temperature tensile strength of 52.1 MPa, while having a tensile strength of 8.0 MPa and an elastic recovery of 71.5 %. Furthermore, the B-EP with iPP LCBs demonstrated excellent compatibility with isotactic polypropylene, enhancing the impact resistance of a 30 wt% B-EP/ commercial isotactic polypropylene blend by 23.5 % compared to a similar compound with commercial EPDM. The study provides valuable insights into optimizing EPM performance by tailoring chain structures through controlled monomer feeding strategies.