Block copolymers of polyethylene and ethylene-propylene-diene elastomer. Synthesis, characterization, and properties

PE-EP and PE-EP-EPDM block polymers have been made in yields exceeding 70% with Ziegler-Natta catalysts by matching the polymerization time for each b lock to chain growth time and catalyst decay rates. A short residence time tubular flow reactor with multiple side stream feeds was used to accomplish this result. The amount of block polymer and chain fragments in the produc t was quantified by various techniques including DSC, solvent fractionation , and GPC/FTIR. PE-EP diblocks have low strength, as expected, and are not suitable for most TPE applications. However, PE-EP-EPDM triblocks with opti mized EPDM block length could be coupled via olefinic unsaturation in the E PDM to form multiarm starlike structures consisting of a central elastomeri c core with the PE blocks extending outward. The coupled triblocks gave pro cessible polymers with tensile strengths of 12-18 MPa and tension sets less than 10%.