Well-defined polymethylene-block-polystyrene (PM-b-PS) diblock copolymers were synthesized via a combination of living polymerization of ylides and atom transfer radical polymerization (ATRP) of styrene. A series of hydroxyl-terminated polymethylenes (PM-OHs) with different molecular weight and narrow molecular weight distribution were prepared using living polymerization of ylides following efficient oxidation in a quantitive functionality. Then, the macroinitiators (PM-MIs ((M) over bar (n) =1900-15 000; PDI =1.12-1.23)) transformed from PM-OHs in approximate to 100% conversion initiated ATRPs of styrene to construct PM-b-PS copolymers. The GPC traces indicated the successful extension of PS segment ((M) over bar (n) of PM-b-PS = 5 000-41 800; PDI = 1.08-1.23). Such copolymers were characterized by H-1 NMR and DSC.