LIVING PSEUDOANIONIC POLYMERIZATION OF EPSILON-CAPROLACTONE - POLY(EPSILON-CAPROLACTONE) FREE OF CYCLICS AND WITH CONTROLLED END GROUPS

In the polymerization of É-caprolactone (eCL) initiated with (CH3CH2)2A10CH3, (CH3CH2)2-A10CH2CH=CH2, or [(CH3)2CHCH2]2A10CH3 and carried out in THF solvent at 20 or 25 °C linear poly(eCL) with 1.03 < Mw/Mn < 1.13 and free of macrocyclics was obtained. Comparison of Mn, calculated and measured, indicated that each initiator molecule starts one macromolecule and that during polymerization transfer reactions, including cyclization, are practically absent. *H and13C NMR studies of the end-group structures revealed that only alkoxy groups (OR') from initiator (R2A10R') were directly involved in initiation. The described polymerization of eCL can be considered as the living process, yielding linear polyesters free from cyclics within the polymerization time required to reach 99% of monomer conversion. Cyclics are produced after much longer time from the linear polymer already formed. The ratios of propagation rate constant (&p(l)) to the rate constants of back-biting, leading to the cyclic dimer (kh(2)), have been used as a measure of kinetic enhancement in linear polymer. For eCL polymerizations carried out in THF at 20 °C and initiated with (CH3CH2)2A10CH3 and [(CH3)2CHCH2]2A10CH3 fcp(l)/feb(2) = 4.6 X 104 and 7.7 X 104 L-mol-1, respectively. These values are substantially higher than for the anionic polymerization of «CL with Na+ counterion (kp(l)/kh(2) = 1.55 X 103 L-mol-1). © 1990, American Chemical Society. All rights reserved.