Effects of crosslinker role reversal on the properties of hydrosilylation-cured silicone elastomers

This study investigates the role of microstructure and functionality of crosslinkers in governing network formation and mechanics in hydrosilylation-cured silicone elastomers. Two end-linked polysiloxane systems were examined, employing silicon-hydride (Si-H) and vinyl (C=C) crosslinking. High-resolution 29Si NMR revealed that the Si-H crosslinker displays a block-like sequence distribution, while the vinyl crosslinker exhibits a more alternating structure. These differences, combined with the high reactivity of Si-H bonds, strongly influenced curing kinetics and network topology. Isothermal rheology at 80 °C showed that the Si-H crosslinking system cured rapidly in a single step (gelation within 50–120 s), forming a dense, heterogeneous network through additional hydride self-condensation. In contrast, the vinyl crosslinking system exhibited a two-step curing process with a prolonged induction period (~400 s) resulting from transient Pt-vinyl complexation, which produced a more homogeneous, loosely cross-linked network. Mechanical testing confirmed the structural influence: Si-H crosslinked elastomers exhibited higher modulus and strength, whereas the vinyl crosslinked systems were softer and more extensible, establishing clear structure-property correlations.