Ring-opening polymerization of a five-membered lactone trans-fused to a cyclohexane ring

The ring-opening polymerization behavior of five-membered lactones fused to a cyclohexane ring (that is, the trans- and cis-hexahydro-2(3H)-benzofuranone denoted T6L and C6L, respectively) was investigated under various conditions. The potassium tert-butoxide (tBuOK)-initiated anionic polymerization of T6L yields polymers with number-average molecular weight (Mn) values of 5000. However, no polymeric products were obtained via cationic and coordination polymerization. Among the anionic initiators, a base stronger than an alkoxide initiated the polymerization of T6L. In contrast, cis-isomer C6L did not polymerize regardless of the initiator species used, which implied an increase in the ring strain of the lactone ring by the transfused cyclohexane. The anionic polymerization of T6L was reversible, and the thermodynamic parameters characterizing the polymerization of T6L were estimated to be Delta H-p degrees = -18 kJ . mol(-1) and Delta S-p degrees = -65 J . K(-1)mol(-1) on the basis of the measurement of the equilibrium monomer concentration.