Octavinyl-POSS as a Modifier of Thermoplastic Polyolefin Elastomers Based on Ethylene-Propylene-Diene and Ethylene-1-Octene EPDM/POEs Blends

Abstract

Thermoplastic polyolefin elastomers (TPOs) were developed from ethylene-propylene-diene (EPDM) rubber and ethylene-1-octene copolymers (POEs) differing in melt viscosity and crystallinity. EPDM/POE blends were prepared at a fixed composition by a melt-mixing process readily applicable to industrial manufacturing. To enhance interfacial interactions and network formation, the blends were modified with octavinyl-polyhedral oligomeric silsesquioxane (POSS) and subsequently crosslinked using dicumyl peroxide (DCP). The rheological behavior of the uncured blends was strongly influenced by the viscosity of the POE phase. POSS incorporation, together with peroxide curing, improved viscoelastic response, as evidenced by Cole–Cole analysis, and promoted curing, resulting in higher cure rate index CRI values and shorter optimum cure times τ90. The introduction of the POE phase increased the storage modulus G′ of the blends, indicating a reinforcing effect. Furthermore, curing and POSS modification enhanced the tensile properties, leading to a pronounced increase in tensile strength and an approximately fourfold improvement in elongation at break. Crosslinking in the presence of POSS reduced the crystallinity of the POE phase and altered the viscoelastic response by restricting polymer chain mobility, thereby reducing stress relaxation and improving creep-recovery performance. Enhanced interfacial interactions were further confirmed by glass transition behavior. As a result, the EPDM/POE/POSS systems exhibited thermo-responsive shape-memory performance, characterized by higher shape fixity F and shape recovery RR ratios.