Enhanced mechanical properties of acrylate and 5-vinyl-2-norbornene-based ethylene terpolymers: rational design and synthesis using remotely modulated phosphine–sulfonate palladium complexes

Abstract

From a practical perspective, it is important to maintain or increase the mechanical properties of functional ethylene copolymers to those of nonpolar polyethylene (PE). In this contribution, we report the enhanced mechanical properties of acrylate- and 5-vinyl-2-norbornene (VNB)-based ethylene terpolymers. Originally, phosphine-sulfonate Pd1 and Pd2 with methyl and phenyl installed para to the sulfonic group were synthesized and characterized. Subsequently, long-chain (but more challenging) polar monomers in which the polar groups combined linearly with double bonds (butyl acrylate (BA) and ethylene glycol monomethyl ether acrylate (EGMA)) were chosen to obtain more flexible chain structures. Crosslinkable and cyclic VNB were used, targeting at rapid crosslinking and enhanced material properties. Ethylene copolymerization and terpolymerization could be efficiently achieved using this strategy, and polymers exhibited improved surface and similar or enhanced mechanical properties compared with those of PE. High activity (2.9 × 10⁷ g (mol h)⁻¹) and high molecular weight (3.8 × 10⁵) were simultaneously observed in ethylene homopolymerization. E-BA(0.64) and E-EGMA(0.87) had a strain-at-break as high as 1016% and 974%, respectively, and stress-at-break up to 45 MPa compared with those of ethylene homopolymer. VNB-based terpolymers E-BA(0.68)–VNB(0.94) and E-EGMA(0.73)–VNB(1) displayed better tensile elongations (723% and 714%) than those of ENB- and DCPD-based terpolymers. Furthermore, though similar thermoplastic properties to PE (strain recovery (SR) = 10%) were observed, enhanced mechanical properties of teropolymers were obtained after sulfur vulcanization, with SR = 19–23% and Δσ (stress differences) = 3.3–10.3 MPa.