Abstract: A retro Diels Alder assisted polymer grafting process in which a Diels Alder adduct is mixed with a polyolefin or polyvinyl polymer substrate and thermally decomposed to form an ethylenically unsaturated monomer which grafts onto the polymer substrate. The monomer conforms generally to the formula R.sub.1 R.sub.2 C.dbd.CHR.sub.3 in which R.sub.1 is hydrogen, methyl or ethyl, R.sub.2 is hydrogen, methyl, ethyl or vinyl and R.sub.3 is a hydroxyl, carboxyl, cyano, formyl, acetyl or propanoyl. The Diels Alder adduct substantially decomposes at a temperature of about 120.degree.-300.degree. C., but does not substantially decompose below about 120.degree. C. The polymer substrate is preferably high-density polyethylene, low density polyethylene, linear low density polyethylene, ethylene-propylene rubber, polypropylene, polystyrene or styrene-butadiene block copolymers. The grafting is induced by, for example, heat, catalyst and/or high shear conditions.