AbstractThe biological degradation of acrylonitrile–dimethylaminoethyl methacrylate and acrylonitrile–acrylic acid copolymers has been studied by evaluating copolymer films in a continuous in vitro rumen system. The copolymer films were examined before and after modification by reaction with ethylene oxide gas. The degradation of the acrylonitrile–dimethylaminoethyl methacrylate copolymer followed a pattern similar to that occurring on thermal degradation. Modification by reaction with ethylene oxide gas, which induces CN conjugation, did not improve the resistance to degradation. The acrylonitrile–acrylic acid copolymer films disintegrated, but on prior modification by reaction with ethylene oxide they remained virtually unaltered. Modification of the acrylonitrile–acrylic acid copolymer results in crosslinking with an absence of CN conjugation, leading to improved resistance to biological degradation.