Tri-n-butylphosphine-catalyzed polyadditions of activated internal diynes (bifunctional beta-substituted propiolate, 1B and 1C) with diols are described. Although a terminal bispropiolate (1A) could not produce soluble polymers, with secondary diols, the polyaddition of 1B or 1C with primary as well as secondary diols gave corresponding polymers (3, only composed of E isomeric units) in high yield. The rate of the present polyaddition was estimated by a model reaction of benzyl alcohol with methyl 2-heptynoate (4), from which the introduction of alkyl groups at the beta-position of propiolate moieties was found to decrease the rate of the reaction by 80 times. Furthermore, the rate-determining step on this polymerization system was speculated to be a protonation step of zwitterionic intermediates with protons from diols.