An NMR study of chain transfer to diols containing both primary and secondary hydroxy groups in the polymerization of epsilon-caprolactone

epsilon-Caprolactone has been polymerized in the presence of various diols, vir propane-1,2-diol (PD), butane-1,3-diol (BD) and hexane-1,5-diol (HD). H-1 and C-13 NMR spectroscopy were used to evaluate the structures. The fin al products were found to be a function of the diol used. It was shown that reactions incorporating PD gave low conversions and/or low degrees of poly merizations when compared with those involving ED or HD. In polymerizations involving ED two C-13 resonances could be seen in the carbonyl region, ass ignable to the ester carbonyls adjacent to the oxymethine and oxymethylene groups derived from the residues of the diol units. Thus, both primary and secondary hydroxy groups were shown to be active in the transfer reaction. Selective decoupling was used to assign the down-field resonance to the car bonyl adjacent to oxymethylene and the up-field resonance to the carbonyl a djacent to oxymethine. However, in the case of the polymerization incorpora ting ED, approximately 10% of end groups were shown to be secondary alcohol s, which are derived from the secondary hydroxy group of ED that does not t ransfer. In polymerizations involving HD only one carbonyl resonance, which could be assigned to an ester adjacent to the diol residue, was observed. From COSY spectra it was possible to assign a peak due to the ester of the secondary hydroxy. The fraction of secondary chain ends was thus observed t o be greater, at cn. 13%, than in the ED polymerizations.