Abstract: Vinyl copolymers containing glycidyl methacrylate as one component are thermal reactive．They are valuable in preparing thermosetting and graft copolymers．When glycidyl methacrylate，methyl methacrylate，and methacrylic acid were copoly-merized，a linear copolymer was formed at first，which，on further heating at higher temperatures．was transformed into a crosslinked polymer．It was shown by IR spectro-scopy that intermolecular reaction of epoxy group and carboxyl group has taken place at the higher temperatures．Crosslinking of the copolymer chains raised the glass tem-perature appreciably．By heating the、glycidyl methacrylate-methyl methacrylate copolymer with polycapro-lactam in benzyl alcohol solution，a graft copolymer was obtained．This graft copoly-met，after being dried，could not be dissolved in most solvents including benzyl alcohol and m-cresol at room temperature，except the very polar ones，such as 98％ formic acid．This abnormal behaviour was ascribed to the formation of H-bonds between molecular chains．Viscosities of both the back—bone copolymer and the graft copolymer in benzyl alcohol and in m-cresol were determined．It was shown that the Huggins constant K'increases owing to grafting in the case of m-cresol solution，but not in the case of benzyl alcohol solution．Therefore，the effect of grafting on the solution viscosity is not always the same as branching，because of the nature of the backbone and that of the graft being different，and hence the solvent effect on them is also different．