Abstract
We report here the Zn(II)-catalyzed convergence of two metastable and isostructural polyesters to an isomeric polymer having a hyperbranched architecture. Ring-opening transesterification polymerization (ROTEP) of 4-carbomethoxyvalerolactone (CMVL) under Bronsted catalysis is known to give the linear polyester PCMVL. We show here that this can be isomerized to the equilibrated (and highly branched) polyester EQPCMVL. Analysis of the fragments obtained from eliminative degradation of EQ-PCMVL were critical in the formulation of its structure. The isomerization of PCMVL to EQPCMVL is a direct consequence of the presence of the second ester functional group in the CMVL ester-lactone, a rarely studied class of monomer. Zn(II)-catalysis of the ROTEP of the isomeric beta-lactone, 2-(2-carbomethoxyethyl)propiolactone (isoCMVL), as well as isomerization of the isostructural linear homopolymer derived from that isomeric monomer, led to the same EQPCMVL. These results suggest a new strategy for the introduction of branching into various polyesters.