Efficient stabilization of thiol‐ene formulations in radical photopolymerization

INTRODUCTION The thiol-ene reaction was first suggested by Posner in 1905, but academic interest in this potential polymerization reaction remained fairly limited until the last two decades. Interest in the thiol-ene reaction mechanism increased as distinct advantages over acrylate homopolymerization were discovered. The thiol-ene polymerization is unique in that it proceeds in general by a step growth radical polymerization. The simplified reaction mechanism of a photo-initiated thiol-ene step growth polymerization for an ene that cannot homopolymerize is well known and is presented in the Supporting Information. Various researchers have shown that unlike (meth)acrylates, thiol-ene reactions have reduced oxygen inhibition with significant lower shrinkage providing materials with often better mechanical properties. In particular, addition of thiols to (meth)acrlyate polymerizations contributes to significant improvement in impact resistance. The thiol-ene step growth radical polymerization leads to a homogeneous crosslinked network with low volume shrinkage and delayed gelation, explaining the reduced brittleness. Because of the wide availability of monomers with different terminal ene groups, it is possible to tailor the physical and mechanical properties of the network structures to meet a diversity of applications.