acrylic acids such as acrylic acid methacrylic acid methyl methacrylic acid and ethacrylic acid and esters thereof may also be stabilized such polymers include polymethylmethacrylate and abs type graft copolymers wherein all or part of the acrylonitrile type monomer has been replaced by an acrylic acid ester or an acrylic acid amide polymers including other acrylic type monomers such as acrolein methacrolein acrylamide and methacrylamide may also be used halogen containing polymers may also be stabilized these include resins such as polychloroprene epichlorohydrin homo and copolymers polyvinyl chloride polyvinyl bromide polyvinyl fluoride polyvinylidene chloride chlorinated polyethylene chlorinated polypropylene fluorinated polyvinylidene brominated polyethylene chlorinated rubber vinyl chloride vinyl acetate copolymers vinyl chloride ethylene copolymer vinyl chloride propylene copolymer vinyl chloride styrene copolymer vinyl chloride isobutylene copolymer vinyl chloride vinylidene chloride copolymer vinyl chloride styrene maleic anhydride terpolymer vinyl chloride styrene acrylonitrile copolymer vinyl chloride butadiene copolymer vinyl chloride isoprene copolymer vinyl chloride chlorinated propylene copolymer vinyl chloride vinylidene chloride vinyl acetate terpolymer vinyl chloride acrylic acid ester copolymers vinyl chloride maleic acid ester copolymers vinyl chloride methacrylic acid ester copolymers vinyl chloride acrylonitrile copolymer and internally plasticized polyvinyl chloride other polymers with which the present improved phosphites and phosphonites are useful include homopolymers and copolymers of cyclic ethers such as polyalkylene glycols polyethylene oxide polypropylene oxide or copolymers thereof with bis glycidyl ethers polyacetals such as polyoxymethylene and those polyoxymethylenes which contain ethylene oxide as a comonomer polyacetals modified with thermoplastic polyurethanes acrylates or.