Two-step copolymerization process by controlling the temperature to prepare copolymer latex containing hard and soft monomer components

Claim 1

An improved process for the preparation of an aqueous emulsion of a copolymer which copolymer comprises from 99 to 30 parts by weight of at least one main monomer selected from the group consisting of styrene, α-methyl styrene, acrylonitrile, alkyl acrylates, alkyl methacrylates, alkyl fumarates, alkyl maleates, wherein the alkyl radical includes radicals of 1 to 12 carbon atoms, vinyl esters and ethers of organic and inorganic acids, vinyl pyridine, chloro allyl carbamate, butadiene and ethylene, from 1 to 30 parts by weight of at least one functional monomer selected from N-methylol derivatives of the formula Y--NR.sub.1 --R.sub.2 wherein R 1 is R 2 or H; R 2 is CH 2 OR 3 ; R 3 is H or C 1 -C 4 alkyl; and Y a 4-benzyl-6-amino triazinyl radical or a R 4 CO-- radical wherein R 4 is CH 2 ═CH--, CH 2 ═C (CH 3 )--, or CH 2 ═CH--CH 2 --; from 0 to 25 parts by weight of an hydroxyl group-containing monomer; and from 0 to 15 parts by weight of an unsaturated aliphatic carboxylic acid wherein the aliphatic group includes radicals of C 2 to C 6 , with the total parts by weight of monomers being 100, which process comprises carrying out the polymerization in aqueous medium, in two stages; the first stage consisting of polymerizing a portion of the above monomers, which does not include the functional monomer when a polymerization temperature above 60° C. is used in the presence of a sufficient amount of an initiator selected from salts of persulphates and peroxyacids; the second stage consisting of continuing the polymerization at a temperature not exceeding 60° C. and at a pH in the range of from 1 to 7, with the addition of the remaining portion of the monomers being made in the presence of an initiator redox system comprising a reducing agent and a peroxide component selected from hydrogen peroxide, ammonium persulphate, organic peroxides and hydro-peroxides, and alkyl percarbonates.