Photocrosslinking of functionalized rubbers, 8. The thiol-polybutadiene system

Abstract

The light-induced crosslinking of polystyrene-block-polybutadiene-block-polystyrene (SBS) was carried out in the presence of a trifunctional thiol and a phosphine oxide photoinitiator. The curing process was followed by infrared spectroscopy, insolubilization and hardness measurements, and was shown to proceed extensively within less than 1 s under intense illumination in air at ambient temperature. The relative reactivity of the thiyl radicals toward the polybutadiene vinyl and butene double bonds was determined, as well as the competition between homo- and copolymerization for the propagating alkyl radical. An increase of the SBS vinyl content from 8 to 59% has little effect on the crosslinking process, because it enhances mainly intramolecular reactions. The thiol/ene polymerization is much more effective to crosslink thermoplastic SBS elastomers than the copolymerization of the polybutadiene double bonds with a diacrylate monomer.