Photocrosslinkable copolymers of 4-vinylbenzyl selenocyanate, 4-vinylbenzyl thiocyanate and 4-vinylbenzyl bromide: Experiments with low-molecular-weight model compounds

The photocrosslinking mechanism of copolymers of styrene (ST) with 4-vinylbenzyl selenocyanate (VBSe), 4-vinylbenzyl thiocyanate (VBT) or 4-vinylbenzyl bromide (VBBr) was investigated using low-molecular-weight model compounds. The photochemistry of benzyl selenocyanate was studied by means of H-1 NMR spectroscopy and gas chromatography/mass spectrometry (GC/MS) analysis. It was found that a cleavage in benzyl and selenocyanato radicals and - to a minor extent - in benzylseleno and cyano radicals occurs. A comparative study of the products which are formed during the photolysis of benzyl selenocyanate, benzyl thiocyanate and benzyl bromide in cumene shows that selenocyanato and thiocyanato radicals have far less hydrogen abstraction efficiency than bromine radicals. The results are discussed in regard to the reactions of the corresponding copolymers. A comparison with a crosslinking mechanism, proposed for chloromethylated polystyrene under irradiation, is carried out.