Polyethers with the allenyl side chains were synthesized by the simultaneous acid-catalyzed reaction of dialdehydes 1, alkylene bis(trimethylsilyl) ethers 2, and 1-trimethylsilyl-2-butyne (4b). Before polymerization, Lewis acid-catalyzed three-component reactions of aldehydes, alkoxysilanes, and propargylsilanes were studied to find that 4b was effective as an allenyl reagent in this reaction. The polycondensations of 1, 2, and 4b were carried out in the presence of 10 mol % of triphenylmethyl perchlorate (TrClO4) at similar to50 degreesC to yield the desired polyethers consisting of 1, 2, and 4b with a molar ratio of 1:1:2 in good yields. This polyether was treated with a cationic catalyst such as BF3OEt2 to give a cross-linked polymer. This polymer synthesis is unusual in that it concurrently constructs both the polymer backbone and the functional side chains from three starting compounds.