ABA-type block copolymers containing segments of poly(dimethyl siloxane) and poly(vinyl pyrrolidinone) were synthesized. Dihydroxyl-terminated poly(dimethyl siloxane) was reacted with isophorone diisocyanate and then with t-butyl hydroperoxide to obtain macroinitiators having siloxane units. The peroxidic diradical macroinitiators were used to polymerize vinyl pyrrolidinone monomer to synthesize ABA-type block copolymers. By use of physicochemical methods, the structure was confirmed, and its characterization was accomplished. Mechanical and thermal characterizations of copolymers were made by stress-strain tests and differential scanning calorimetric measurements. (C) 1999 John Wiley & Sons, Inc.