Rubbery carboxylated acrylate polymer, latex, and preparation thereof

Abstract

A novel latex is derived from a crosslinked carboxylate latex containing from 1-20 phr of itaconic acid (IA) and at least 70 phr of one or more copolymerizable monomers one of which is an acrylate having the structure ##STR1## wherein R.sub.1 is hydrogen or methyl; R.sub.2 represents C.sub.1 -C.sub.20 alkyl, C.sub.2 -C.sub.7 alkoxyalkyl, C.sub.2 -C.sub.7 alkylthioalkyl, or C.sub.2 -C.sub.7 cyanoalkyl; and at least 40 phr of said acrylate in said film is present as an alkyl acrylate in which alkyl is C.sub.4 -C.sub.8. The latex can only be formed in an aqueous medium by an emulsion polymerization process in which at least one-half of the IA is initially charged into a reactor, and the remaining ingredients of the recipe then added gradually. This unique order of addition produces a highly stable latex of polymer particles having a glass transition temperature (T.sub.g) in the range from about -20.degree. C. to about -60.degree. C., and having on their surfaces, a concentration of carboxyl (COOH) groups which is at least twice that of COOH groups on particles of a latex formed by conventionally proportioning the monomer ingredients after initiation. The unique distribution of COOH groups permits the latex to be sprayed, for example on a non-woven fabric, without plugging the nozzle of a commercial spray gun, and imparts unexpectedly high blocking resistance to the non-woven. The unique characteristic concentration of carboxyl groups persists in an elastomeric film obtained by removing volatiles from the coalesced polymer particles. A self-supporting film is soft, but tough, with a raw tensile strength of at least 300 psi, at elongation of at least 350%, and exhibits less than 20% hysteresis loss.