The process disclosed herein involves the bromination of copolymers of non-terminal acetylenic methacrylates and the brominated products produced thereby. Acetylenic methacrylate polymers upon dibromination of the acetylene group give ethylenic dibromo derivatives which are hydrolytically stable. In comparison the derivative obtained upon dibromination of a polymer of allyl methacrylate has dibromopropyl methacrylate repeating units which are susceptible to hydrolysis of the bromine. Thus where it is desired to impart flame resistant properties to a polymer it is possible to impart both flame resistance and hydrolytic stability by dibromination of corresponding copolymers containing repeating units of the formula
-CH2C(CH3)- COOCH(R )C=CR
wherein R’ is H or R", and R" is a hydrocarbon radical of 1-8 carbons. Where higher proportions of bromine are desired and hydrolytic stability is of less importance, tetrabromination can be effected.