Block copolymers containing segments of poly(ethylene oxide) and polystyrene were synthesized. Dihydroxyl-terminated polyethers (PEG-4000 and PEG-20,000) were reacted with an aliphatic diisocyanate (3-isocyanatomethyl-3,5,5-trimethyl-cyclohexyl-isocyanate) and with an aliphatic hydroperoxide (t-butyl hydroperoxide). The resulting polymeric peroxycarbamates were used as free radical initiators for vinyl polymerization. Formation of block copolymers was illustrated by several characterization methods such as chemical and UV analysis, infrared spectroscopy, and DSC thermograms. Mechanical characterization of the copolymers was made on the basis of the stress—strain curves obtained from a mechanical testing instrument (Tensilon).