Core-shell composite polymers having high amounts of carboxylic acid units in the shell

Claim 1

A core-shell composite polymer having a soft polymer core and a two layered shell having up to about 40 mole percent of methacrylic acid units therein, said core-shell composite polymer being produced by a process comprising the steps of: (a) providing, as the core polymer, an emulsion comprising discrete particles of a soft polymer of butadiene or copolymer of ethylene and vinyl acetate in an aqueous vehicle, (b) adding to the emulsion, as a monomer to form an inner layer of the shell, methylmethacrylate in an amount sufficient to form, upon polymerization, a substantially complete enclosure around the particles of the core polymer, (c) reacting the emulsion under conditions effective to polymerize the methylmethacrylate to form discrete soft polymer core particles which are completely encased by an integral enclosure of poly(methylmethacrylate), but are free of methylmethacrylate at least in the center thereof, (d) further adding to the emulsion, as monomers to form an outer layer of the shell, a mixture of methylmethacrylate and methacrylic acid in molar ratio of from 1:3 to 3:1, in an amount sufficient to form, upon polymerization, a substantially complete enclosure around the encased particles of the core polymer, and (e) reacting the emulsion, under conditions effective to copolymerize the methylmethacrylate and methacrylate acid, thereby forming around the encased polymer particles produced in step (c) an integral outer shell layer of a copolymer of methylmethacrylte and methacrylate acid.