AB block copolymers of methyl vinyl ether (MVE) and styrene were synthesized by the sequential living cationic polymerization. The first-stage polymerization was with MVE and was initiated in methylene chloride solvent at -78-degrees-C with the adduct [1; CH3CH(OiBu)Cl] of hydrogen chloride and isobutyl vinyl ether (IBVE) as an initiator in conjunction with tin tetrachloride (SnCl4; a Lewis acid activator) and tetra-n-butylammonium chloride (nBu4NCl; an added salt). To the solutions of the resultant living poly(MVE) at -78-degrees-C (conversion approximately 100%) were sequentially added styrene and a mixture of SnCl4 and the salt. Under these conditions, the added styrene remained virtually intact, but upon warming the solution to -15-degrees-C a smooth and quantitative second-stage polymerization ensued to give the target MVE-styrene block copolymers with narrow molecular weight distributions in high yield (>80 wt %). When solution-cast from toluene, the isolated block copolymers (typically, MVE/styrene = 21/33 in DP(n) by H-1 NMR) gave nonsticky, transparent, homogeneous films that completely differed from the corresponding cast products from homopolymers of MVE and styrene as well as from their blends. Similar AB block copolymers were also prepared from 2-chloroethyl vinyl ether and styrene. The key to these successful block copolymerizations is the development of an initiating system (1/SnCl4 with added nBu4NCl) that induces living cationic polymerizations of both styrene and MVE and the other vinyl ethers, along with the judicious adjustment of the polymerization conditions for each of the comonomers.