Simple and efficient synthesis and functionalization of well-defined, linear telechelic polycarbonates by reversible polycondensation through alkoxide exchange reaction

Abstract

We investigated the synthesis of telechelic polycarbonates free from cyclic polymers by means of reversible polycondensation of diol formate 1 and dipropyl carbonate (2) under reduced pressure, using an excess of either reagent in the presence of 5 mol% potassium tert-butoxide (^tBuOK) as an alkoxide exchange catalyst. In the polycondensation of dodecane-1,12-diol diformate (1a) with excess 2 in diglyme, linear polycarbonates with a propyl carbonate moiety at both ends were obtained free from cyclic polymer. The M_n value of the obtained polymer was increased to 6510 when the amount of 2 was decreased to 1.10 equivalents, while the propyl carbonate ends remained. However, the polycondensation using 1.05 equivalents of 2 afforded polycarbonate with a hydroxyl end and cyclic polymer, although the molecular weight was higher than 13000. This result can be explained in terms of the evaporation of 2, which has a low boiling point, during the polymerization under reduced pressure. On the other hand, the polycondensation of excess 1a with 2 in bulk yielded linear polycarbonates with a hydroxyl group at both ends. The M_n value increased to 10,100 as the amount of 1a was decreased to 1.04 equivalents, while the hydroxyl ends remained. Furthermore, the polycondensation of equimolar 1a with 2 in the presence of functional carbonate 3 or functional diol ester 4 afforded telechelic polycarbonates with functional groups derived from 3 or 4 at both ends.