Improved understanding on the reinforcement of low-temperature hydrogenated nitrile butadiene rubber composites by in situ polymerization of unsaturated metal methacrylate: influences of salt cation
In situ reaction of unsaturated metal methacrylate (UMM) has captured scientists’ attention due to its importance in reinforcing low-temperature-grade hydrogenated acrylonitrile butadiene rubber (LTG-HNBR). In this article, LTG-HNBR composites with in situ polymerized sodium (Na+), magnesium (Mg2+) and aluminum (Al3+) methacrylates were successfully fabricated for the purpose of investigating the roles of their salt cations on the reinforcement of the rubber. When the cation valence rose, UMM self-polymerized to produce poly(UMM) and then converted to hybrid structures including poly(UMM) and grafting components to the rubber chains; even unreacted aggregations of UMM during the vulcanization of the matrix. Low solubility of UMM with trivalent cation (Al3+) complicated the composite system, decreasing its conversion of poly(UMM) and growing polymethylacrylic acid. Once UMM was fully dissolved, the poly(UMM) developed into fine, dispersed nanoparticles. Monovalent cation (Na+) drove these dispersed particles to arrange as band-like nano-topographies. Reinforcement of the rubber matrix was greatly affected by the generation of poly(UMM) where a tiny amount of aluminum polymethacrylate (i.e. poly(AlMMA)) gave rise to poor reinforcements. So the morphology and chemical structure of poly(UMM) and the solubility of UMM induced by its cations have a remarkable impact on reinforcement of rubber matrices. We believe that choosing the cation species of UMM may be a simple method to control the reinforcement of rubber composites.