Macromolecular engineering of polylactones and polylactides .19. Kinetics of ring-opening polymerization of epsilon-caprolactone initiated with functional aluminum alkoxides

End-functional aliphatic polyesters have been synthesized by ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL) and lactides (LA). Polymerization initiated with any of the functional aluminum alkoxides of the general structure Et(3-p)Al(OCH(2)X)(p), where p = 1 and 3, obeys a living ''coordination-insertion'' mechanism, under suitable conditions (temperature, concentration, and solvent), with the formation of alpha-functional chains of a predictable molecular weight. A kinetic study has emphasized the importance of the cyclic monomer (epsilon-CL or LA) and the key role of the initiator structure: the number of functional alkoxides per aluminum and the nature of the functional group (X = CH2Br, (CH2)(2)CH=CH2, (CH2)(2)NEt(2)). Activation enthalpy and entropy have been calculated for the epsilon-CL polymerization initiated by several aluminum alkoxides at various temperatures. The effects of solvent (toluene or tetrahydrofuran) and purification of the aluminum monoalkoxides by distillation under reduced pressure have also been considered.