Dimethyldiphenylsiloxane copolymers were obtained by hydrolysis-copolymerization of diphenyldichlorosilane with octamethylcyclotetrasiloxane in the presence of water. A sulfonic cationite VIONIT CS-34C was used as catalyst. A macroporous, strongly basic anionite or a weakly basic gel were used to neutralize the HCl formed during the reaction. The formation of the copolymer was confirmed by Si-29 n.m.r.