In situ copolymerization behaviour of zinc dimethacrylate and 2-(N-ethylperfluoro-octanesulphonamido)ethyl acrylate in hydrogenated nitrile-butadiene rubber during peroxide crosslinking

The in situ copolymerization behaviour of zinc dimethacrylate (ZMA) and 2-(N-ethylperfluoro-octanesulphonamido)ethyl acrylate (RfSA) in hydrogenated nitrile–butadiene rubber (HNBR) initiated with di-tert-butyl peroxy di-isopropylbenzene (PO) was studied by transmission electron microscopy, dynamic mechanical analysis, surface tension and surface composition. About 80% of the monomers were copolymerized within the half-lifetime of PO at 140 °C. The compositions of the copolymers were almost the same as the co-monomer compositions at high conversions. The crosslinking of the HNBR proceeded within the press time of 300 min. At the initial stage of the copolymerization, ZMA seemed to form cluster domains in the HNBR matrix, followed by a decrease in the domain size to become too small to exhibit a tanδ peak of the clusters on phase separation between the matrix and the copolymer. The surface compositions were different from the average compositions. The RfSA unit in the copolymer was segregated at the surface of the vulcanizates with an increase in the press time. During phase separation and migration of the copolymer towards the surface, Zn and N were oxidized and ionized. Finally, the in situ copolymerizations formed a continuous network structure of which the domain size was 30–60 nm.