Faster and greater moisture curing ethylene‐silane copolymers with good shelf stabilities

Abstract Vinyltrimethoxysilane (VTMS) functionalized ethylenic polymers, in the form of reactor‐made ethylene‐silane copolymers as well as post‐reactor made silane‐grafted ethylene polymers, were evaluated for the purpose of moisture‐induced crosslinking through hydrolysis and condensation reactions. The copolymers were of 1.6 wt% or 4.2 wt% VTMS contents, and the silane‐grafted resins ranged in VTMS contents from 1.1 to 3.7 wt%. The silane‐grafted materials were very reactive under humid conditions at room temperature, resulting in very poor shelf stabilities manifested in sharp drops in their melt indices over time (changes that in the early stages were dominated mostly by resin molecular weight distribution and/or branching, and in the later stages much more by silane content). In sharp contrast, the ethylene‐silane copolymers exhibited outstanding shelf stabilities over time even at relatively high silane content, indicating desirably low reactivities in the absence of moisture‐cure catalyst. When formulated with catalyst, and exposed to humid conditions, the cure characteristics of the silane functionalized ethylene polymers varied significantly, with the fastest and greatest crosslinking observed using the ethylene‐silane copolymer of 4.2 wt% VTMS content and remarkably excellent shelf stability. Analyses of reaction rates revealed very interesting trends, depending on type of catalyst (tin or sulfonic acid) and resin. Highlights Ethylene‐silane copolymers and silane‐grafted ethylene polymers were studied. Copolymers exhibited vastly superior shelf stabilities than grafted materials. Catalyst type and loading affected moisture‐induced crosslinkability. Increased silane content in copolymer led to faster and greater crosslinking. Best balance of crosslinkability and shelf stability obtained with copolymers.