Photocrosslinking of functionalized rubbers. X. Butadiene-acrylonitrile copolymers

The photocrosslinking of polyacrylonitrile-block-polybutadiene-block-polyac rylonitrile (ABA) was shown to proceed within seconds at ambient temperatur e upon UV exposure in the presence of an acylphosphine oxide photoinitiator . The curing process was followed by infrared spectroscopy, insolubilizatio n, and hardness measurements. Complete insolubilization could not be achiev ed with the neat ABA rubber because of the poor reactivity of the 2-butene double bond and the low vinyl content of the polybutadiene chain. The addit ion of multifunctional acrylate monomers (20 wt %) causes a substantial inc rease of both the reaction rate and the crosslink density of the polymer, w hich becomes completely insoluble in toluene in less than 1 s upon UV irrad iation. An even greater effect was observed by using small amounts (1 wt %) of a trifunctional thiol crosslinker. Both the thiol and the photoinitiato r concentrations were shown to affect the kinetics of the thiol-ene polymer ization and the polymer network crosslink density. A direct relationship wa s found to exist between the swelling degree of the UV-cured rubber and the interchain molecular weight of the network. (C) 2001 John Wiley & Sons, In c.