On the cyclo-depolymerization of alkyl aromatic polyesters and the in situ polymerization of the cyclic oligomers produced

Macrocyclic oligomers (MCOs) of some commercial alkyl aromatic polyesters (PET, PTT, PBT) were prepared by cyclo-depolymerization (CDP) of the polymers in refluxing 1,2-dichlorobenzene with di-n-butyltin oxide as a transesterification catalyst. The mixtures of MCOs and residual polymer obtained at varying polymer/solvent ratios were separated and characterized by thorough GPC and DSC analyses. The higher the initial polymer concentration the lower was the yield of MCOs, and vice versa. Rheological measurements carried out on polymer/MCO mixtures showed a decrease in the melt viscosity with increasing amount of MCOs. Moreover, the MCOs present in these systems easily underwent entropically-driven ring-opening polymerizations (ED-ROPs) to reform the parent polyesters.