Grafting acrylic acid onto starch and poly(vinyl alcohol) by photolysis

Grafting Acrylic Acid onto Starch and Poly( vinyl Alcohol) by Pho tolysisAcrylic acid graft polymerizes onto starch with low add-on in chemically initiated free radical systems such as ceric ion or ferrous iron-hydrogen peroxide.'Higher add-on is obtained using y radiation or electron beam preirradiation.2Irradiation of an aqueous monomer solution in a thin layer has been shown to be effective in maximizing conversion of monomer to p ~l y m e r .~We find that we can graft acrylic acid onto granular starches and poly(viny1 alcohol) by photolysis in a novel cyclic process whereby a slurry of the material in water is pumped continuously past a quartz cell and irradiated while adding acrylic acid.The cell is wrapped with a polyethylene sheet transmitting light a t wavelengths longer than 250 nm.This sheet prevents homopolymer from sticking to the quartz element and facilitates good recovery of product.Acrylic acid is added dropwise to minimize homopolyber formation by providing a maximum initial starchmonomer ratio.The method is applicable to ordinary, high-amylose, thin-boiling, oxidized, acid-modified, and hydroxyethylated starches as well as granular poly(viny1 alcohol).Graft copolymers with up to 20% add-on of poly(acry1ic acid) are obtainable.Monomer goes 40-66% to graft copolymer and 19-36% to homopolymer.The graft copolymers give clear, thick pastes when heated in aqueous alkali.