Anionic copolymerization of ethylphenylketene (EPK) with 4-(tert-butyldimethylsilyloxy)benzaldehyde (SiO-BA) was carried out using butyllithium as an initiator in THF at -40 degreesC. The copolymerization proceeded via 1:1 alternation, generating the corresponding polyester having silyl protected phenol moiety in the side chain quantitatively. By addition of lithium chloride to the polymerization system, the polymerization proceeded in a living fashion to afford the corresponding polyester having narrow molecular weight distribution (M-w/M-n < 1.2). Treatment of the obtained polymer with tetrabutylammonium fluoride in the presence of acetic acid resulted in complete removal of the silyl group without main chain degradation to afford polyester having phenol moiety, which was soluble in methanol. Thermal degradability of the polyester with phenol moiety Was considerably higher than that of the silyl-protected polymer, suggesting that the acidity of the phenol moiety would promote thermal dissociation of the polyester main chain.