Emulsion copolymerization process

An aqueous emulsion polymerization process for preparing homogeneous, low molecular weight alkali soluble polymer from a water insoluble vinylic monomer and acrylic acid which comprises:

• (a) forming an aqueous precharge consisting essentially of sufficient acrylic acid to inhibit formation of homopolymers of said water insoluble vinylic monomer and to promote formation of a homogeneous copolymer of said water insoluble vinylic monomer and acrylic acid, said precharge being initiator free;
• (b) adding a comonomers charge of said water insoluble vinylic monomer and acrylic acid to said acrylic acid precharge in the presence of an initiator and a chain transfer agent, wherein the weight ratio of said comonomers in said charge corresponds to a preselected ratio of said comonomers in said alkali soluble polymer and wherein the addition rate of said comonomers charge is no greater than the polymerization rate for said comonomers at a steady state condition;
• and wherein (1) the polymerization reaction is starved of water insoluble monomer and (2) the initiator is added to the emulsion polymerization reaction mixture immediately preceding and/or simultaneously with the comonomers charge;
• and
• (c) maintaiing a sufficient solids concentration during said polymerization reaction to reduce the tendency of acrylic acid to partition into the aqueous phase.