PURPOSE: A chlorine resin of a specific chlorine content is made to react with an unsaturated compound to effect the modification of the resin, whereby the titled composition is produced, which is suitably used as a vehicle for coating and adhesive, because of its high weathering resistance, corrosion resistance and high stability.

CONSTITUTION: A chlorine resin of less than 50wt% chlorine content such as chlorinated polypropylene is modified by effecting the reaction with an unsaturated compound, for example, in a solvent such as xylene in the presence of a catalyst of nickel oxide, preferably at 60W80°C for 1W6 hr to produce the objective composition. The preferable unsaturated compound is, e.g., vinyl compound, vinylidene compound, unsaturated carboxylic acid, allylic compound or conjugated double bond compound such as polybutadiene homopolymer.