Aqueous polymer dispersions

摘要

An aqueous polymer composition is described comprising a homogeneous acrylic polymer dispersion produced by emulsion polymerization of a monomer mixture comprising: (A) from 85 to 99.9 wt % of one or more main monomers selected from C1-C12-alkyl esters of acrylic acid or C5-C12-alkyl esters of methacrylic acid, styrene, and vinyl toluene in such a ratio as to produce a polymer having a Tg in the range of −20 to +65° C.; and (B) from 0.1 to 5 wt % of at least one stabilizing monomer selected from ethylenically unsaturated monocarboxylic acids or amides thereof, ethylenically unsaturated dicarboxylic acids or anhydrides or amides thereof, ethylenically unsaturated sulfonic acids, ethylenically unsaturated phosphoric acids, and ethylenically unsaturated phosphonic acids. The emulsion polymerization is conducted in the presence of 0.05 to 3 wt %, based on the total weight of monomers in the monomer mixture, of a chain transfer agent (C).

主权项

1. An aqueous polymer composition comprising a heterogeneous polymer dispersion prepared by a stepwise emulsion polymerization process comprising polymerizing in a first stage a first monomer composition comprising:
(A1) from 50 to 80% by weight of at least one main monomer whose homopolymer has a glass transition temperature below about 0° C.; (A2) from 19.3 to 50% by weight of at least one main monomer whose homopolymer has a glass transition temperature above about 65° C.; and (B) from 0.5 to 5% by weight of at least one stabilising monomer selected from ethylenically unsaturated monocarboxylic acids or amides thereof, ethylenically unsaturated dicarboxylic acids or anhydrides or amides thereof, ethylenically unsaturated sulfonic acids, ethylenically unsaturated phosphoric acids, and ethylenically unsaturated phosphonic acids; and wherein the first polymerization stage is conducted in the presence of 0.05 to 3 wt %, based on the total weight of monomers in the first monomer composition, of a chain transfer agent (C) to produce a first polymer phase having a Tg less than or equal to 20° C.; and polymerizing in a second stage, and in the presence of the first polymer phase, a second monomer composition comprising: (A1) from 5 to 45% by weight at least one monomer whose homopolymer has a glass transition temperature below about 0° C.; and (A2) from 65 to 90% by weight at least one monomer whose homopolymer has a glass transition temperature above about 65° C. to produce a second polymer phase having a Tg of at least 40° C.