Polyethers with allyl side chains were synthesized by the simultaneous acid-catalyzed reaction of dialdehydes (1), alkylene bis(trimethylsilyl) ethers (2), and allyltrimethylsilane (3). The reactions of 1, 2 and 3 were carried out in the presence of 10 mol% of triphenylmethyl (trityl) perchlorate at -55 degrees C to yield polyethers having allyl groups in the side chains. When the dialdehyde having the ester moieties as 1, ethylene bis(trimethylsilyl) ether and 1,4-bis(trimethylsiloxy)cyclohexane as 2 were used, high molecular weight polymers were obtained. In the polymerizations at ambient temperature, the polymer was precipitated during the reaction because of crosslinking between the aromatic rings via a trityl perchlorate assisted Friedel-Crafts reaction. The soluble polyether with the allyl side chains reacted with 1,2-ethanedithiol in the presence of a radical initiator in benzene at 60 degrees C to yield a crosslinked polymer quantitatively within 1 h. This polymer synthesis is unusual in that it concurrently constructs both the polymer backbone and the functional side chains from three monomers.