Copolymer latex and paper coating composition thereof

A copolymer latex comprising 25 to 45 percent by weight of a conjugated diolefinic monomer, 3 to 40 percent by weight of an alkyl ester of an unsaturated carboxylic acid, selected from the group consisting of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, cyclohexyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate and mixtures thereof, 1 to 5 percent by weight of a hydroxyalkyl-containing unsaturated monomer selected from the group consisting of .beta.-hydroxyethyl acrylate, .beta.-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, di(ethylene glylcol) itaconate, di(propylene glycol) itaconate, bis(2-hydroxypropyl) itaconate, bis(2-hydroxyethyl itaconate, bis(2-hydroxyethyl) fumarate, bis(2-hydroxyethyl) maleate, 2-hydroxyethyl methylfumarate, 2-hydroxyethyl vinyl ether, hydroxymethyl vinyl ketone, allyl alcohol and mixtures thereof, 0.5 to 4 percent of an unsaturated carboxylic acid monomer and the remaining percent of an alkenyl aromatic monomer.