A cationic ring-opening polymerization of a cyclic ether ("CE") in conjunction with an unsaturated alcohol (propagator) having an allyl double bond, produces a polyether macromer having an allylic group near one end and a hydroxyl group at the other. The polymerization proceeds by polyaddition of the CE to the OH group which is the propagating species. The CE is an alkylene oxide or an aliphatic or aromatic glycidyl ether; the propagator is a primary or secondary alcohol which, if cyclic may have a single internal double bond in one ring. The catalyst is a Friedel-Crafts acid, strong protic organic or inorganic acid, oxonium salt, or the like. The macromer formed may be homopolymerized to yield a polyvinyl homomacromer with pendant chains of polymerized CE; or the CE may be copolymerized with a wide variety of olefinically unsaturated monomers to form a macromer copolymer; or, plural cyclic ethers may be (a) sequentially polymerized to form macromer block copolyethers, or, (b) polymerized randomly to form macromer copolyether copolymers. The cationically ring-opened macromer formed always contains a trace of a cyclic oligomer of the CE.