Modification of polysiloxanes by free-radical addition of pyridylthiols tothe vinyl groups of the polymer

Polysiloxanes containing pyridyl groups were prepared by thiol-ene addition to vinyl side groups of polysiloxanes. Apart from polymethylvinylsiloxane, poly(methylvinylsiloxane-co-dimethylsiloxane)s synthesized by three differ ent methods were used: (1) equilibrium copolymerization of 1,3,5,7-tetramet hyl-1,3,5,7-tetravinylcyclotetrasiloxane (V-4) with hexamethylcyclotrisilox ane (D-3); (2) kinetically controlled homopolymerization of 1-vinyl-1,3,3,5 ,5-pentamethylcyclotrisiloxane; and (3) kinetically controlled copolymeriza tion of V-4 and D-3, which permitted us to obtain siloxane copolymers with different arrangements of the pyridyl groups along the chain. Addition of 2 -(4-pyridyl)ethanethiol (PET) to the vinyl groups of these polymers proceed ed with high yields, leading preferentially to beta-addition products, The addition of 4-pyridylthiol (PT) proceeded much less readily. Polymers were characterized by FT-IR, H-1 and C-13 NMR. and by thermal analytical methods . (C) 1999 Elsevier Science Ltd. All rights reserved.