Dimethyl 5-hydroxyisophthalate undergoes a base-catalyzed nucleophilic oxirane ring-opening addition reaction with allyl glycidyl ether, to afford 5-substituted derivatives of isophthalic acid. Influence of third component, i. e. a series of 1,ω-alkanediols on the copolymerization reaction of dimethyl 5-hydroxyisophthalate with poly(ethylene glycol) has been studied. Lipase-catalyzed condensation polymerization of dimethyl 5-hydroxyisophthalate with polyethylene glycol is reported.