Disclosed herein is a process for the production of a polysiloxane-polyorgano block copolymer. The process includes reacting a reaction mixture containing (a) an ester-functional polydiorganosiloxane and (b) a bisphenolic compound or a bisphenolic compound oligomer. This process has the advantage of yielding block copolymers with controlled block structures and avoiding the impurities that may be carried over from the conventional hydroxyaryloxy-terminated-polydiorganosiloxanes.