Polysiloxane graft copolymers, flexible coating compositions comprising same and branched polysiloxane macromers for preparing same

A solvent based flexible coating composition, useful as an automotive coating on metal and plastic substrates, comprising:

• (A) hydroxy functional polysiloxane graft copolymer of number average molecular weight between about 1,000 and about 15,000, having a hydroxyl number between about 30 and about 300, and being the reaction product of carbon-carbon double bond-reactive monoethylenically unsaturated monomer with hydroxy functional carbon-carbon double bond-bearing branched polysiloxane macromer, under free radical polymerization reaction conditions, said monomer bearing substantially no functionality which is substantially reactive with hydroxy functionality of said macromer under said reaction conditions, which macromer is the reaction product of (i) epoxy monomer having the formula:
• ##STR8## wherein R is hydrogen or C1 to about C7 alkyl, and R' is C1 to about C7 alkyl or COO(CH.sub.2).sub.n, n being 0 to about 7, with (ii) hydroxy functional polysiloxane reactant having about 0-10 urethane groups per molecule comprising oligomeric straight chain polysiloxane having a number average molecular weight between about 1,000 and about 10,000 and hydroxyl number between about 30 and about 300;
• and
• (B) polyfunctional, hydroxy-reactive crosslinking agent selected from aminoplast crosslinking agent, polyisocyanate crosslinking agent, blocked polyisocyanate crosslinking agent comprising at least two ioscyanate groups blocked by reaction with active hydrogen bearing blocking agent, (and) or (compatible) mixture of any of them, said crosslinking agent being included in an amount sufficient to provide, at a cure temperature of said composition, between about 0.5 and about 1.6 hydroxy reactive groups per hydroxy group contributed by said hydroxy functional polysiloxane graft copolymer.