Photocrosslinking of functionalized rubbers, 7. Styrene-butadiene block copolymers

Abstract

The photocrosslinking of polystyrene-block-polybutadiene-block-polystyrene (SBS) was studied by means of infrared spectroscopy, by monitoring the disappearance of the pendent vinyl double bonds, which was shown to proceed within a few seconds upon UV exposure in the presence of an acylphosphine oxide photoinitiator. Complete insolubilization requires the reaction of 17 double bonds per polymer chain for an SBS sample containing 8% vinyl groups. An increase of the vinyl content has little effect on the crosslinking process, because it enhances mainly intramolecular reactions. A paraffinic oil proved to be an effective plasticizer for the photocrosslinked elastomer. The addition of a telechelic acrylate oligomer causes a substantial increase of both the reaction rate and the final degree of conversion of the SBS double bonds. The light-induced copolymerization of the vinyl and butene double bonds with the acrylate double bonds leads to the formation of a hard and flexible polymer material within a fraction of a second.