PURPOSE: To obtain the subject copolymer with a distinctive release characteristics and being useful as a release coating advantageously in cost by copolymerizing a specified free-radical polymerizable monomer and a mercapto-functional silicone compd. in the presence of an initiator.

CONSTITUTION: A free-radical polymerizable monomer (A) mixed with a solvent for obtaining a feeding material with an effective dielectric const. of at least 2.5, a mercapto-functional silicone compd. (B) of formula [wherein R1 is an alkyl, etc.; R2 and R4 are each divalent bonding value; R3 is an alkyl, an aryl, etc.; R5 and R6 are each an alkyl, an aryl and -ZSH (wherein Z is a divalent bonding group); x and q are each 0-3; y≥10] and an initiator (C) which can form a free radical by being exposed to a polymn. initiating means (pref., thermal decomposition, etc.,) are mixed to initiate free-radical polymn. and the polymn. is continued until an aimed copolymer is formed.