Polydiorganosiloxane/thiuram disulfide block copolymers and radical polymerization of vinyl monomers therewith

A polydiorganosiloxane/thiuram disulfide block copolymer having the formula:

• ##STR19## in which the symbols R.sub.1, which may be identical or different, are each a linear or branched C.sub.1 -C.sub.2 alkyl radical optionally interrupted by an oxygen or nitrogen heteroatom and optionally substituted by a tertiary amine group, a C.sub.3 -C.sub.8 cycloalkyl radical, or an aryl, aralkyl or alkylaryl radical;
• the symbols Y, which may be identical or different, are each a divalent organic radical bonded to the silicon atom via an Si--C bond;
• the symbols R.sub.2, which may be identical or different, are each a linear or branched C.sub.1 -C.sub.12 alkyl radical, a 3,3,3-trifluoropropyl radical, or a phenyl radical;
• the symbols R.sub.3, which may be identical or different, are each a radical R.sub.2 or an alkoxy radical having from 1 to 8 carbon atoms;
• m is an integer ranging from 0 to 500;
• and n is an integer ranging from 2 to 100.