Block copolymers containing segments of poly(dimethylsiloxane) (PDMS) and polystyrene were synthesized. Dihydroxy terminated PDMS M(n) 2500 g/mol, was reacted with an aliphatic diisocyanate (isophorone diisocyanate) and an aliphatic hydroperoxide (t-butyl hydroperoxide). The resulting polymeric peroxycarbamate having siloxane units (a new macroinitiator) was used as free radical initiator for vinyl polymerization of styrene. Formation of block copolymers was illustrated by several characterization methods such as chemical and spectroscopic analysis, fractionation, and GPC. Mechanical and thermal characterization of the copolymers were made by stress-strain tests and DSC. The surface properties and the morphology of the block copolymers were investigated by contact angle measurements and SEM. (C) 1996 John Wiley & Sons, Inc.