Preparation and characterization of silicone rubber with high modulus via tension spring-type crosslinking

High-molecular-weight poly[(aminopropyl)methylsiloxane-co-dimethylsiloxane] (P2) and poly[(aminoethylaminopropyl)-methylsiloxane-co-dimethylsiloxane] (P3) were synthesized through base equilibration of 3-aminopropylheptamethylcyclo-tetrasiloxane or N-β-aminoethyl-γ-aminopropylheptamethylcyclotetrasiloxane with octamethylcyclotetrasiloxane. These materials were crosslinked with oligo[(acryloxypropyl)methylsiloxane-co-dimethylsiloxane] (AP-PDMS) via an aza-Michael reaction to produce novel silicone rubbers. Diaddition and triaddition reactions occurred between the aminopropyl groups of P2 and the aminoethylaminopropyl groups of P3 with the acyl groups of AP-PDMS. This led to the higher modulus of novel silicone rubbers prepared via “tension spring-type crosslinking” compared with that of the silicone rubber prepared from poly[(piperazinylpropyl)methylsiloxane-co-dimethylsiloxane] (P1) via monoaddition reaction. Crosslinking mechanism was proven by solid-state 13C NMR and Fourier transform infrared spectroscopy. Curing characteristics were measured through cure curves conducted on rheometry. The postcure conditions and the ratio of crosslinkers used were investigated in detail. Analysis of mechanical properties showed that tension spring-type crosslinking improved the modulus of silicone rubber based on P2 or P3.