A comb copolymer consisting of a methacrylic macromonomer as a branch ingredient and acrylic ester as a backbone ingredient and being suitable for an acrylic elastomer material which is excellent in transparency, weatherability and mechanical strength; an impact resistant acrylic resin composition obtained by blending the above comb copolymer with a PMMA (co)polymer; and a comb copolymer similarly consisting of a methacrylic macromonomer as a branch component and acrylic ester as a backbone component and being an acrylic resin which is excellent in transparency, weatherability, gloss and light resistance, are disclosed in this invention.Preparation methods of the high molecular weight comb copolymers useful for molding materials comprising the above mentioned comb copolymers are disclosed. The disclosed preparation methods comprise, in the copolymerization of the macromonomer having a vinyl group at one end of the main chain with a vinyl monomer, conducting aqueous suspension polymerization of the monomer mixture in the presence of an initiator in a solvent which is a good solvent for the macromonomer and has a solubility of 10% by weight or more in water at 30.degree. C., or conducting aqueous suspension polymerization of the monomer mixture in the presence of an initiator in a halogenated hydrocarbon solvent which is a good solvent for the macromonomer and has an azeotropic point with water ranging from 30.degree. to 90.degree. C. at a temperature above said azeotropic point.