N.m.r. spectroscopy of polyesters from bridged bicyclic lactones

Abstract The 13 C n.m.r. spectra of some polyesters produced by anionic ring-opening polymerization of 2-oxabicyclo[2,2,2] octan-3-one are reported and discussed. From a comparison with the spectrum of the monomer and by hydrolysis of the polymer, it was possible to assign to the polymer, obtained using n-butyllithium as a catalyst, a microstructure in which the ester groups on the 1 and 4 positions of the cyclohexane unit are cis to each other. The polymers obtained both by sodium tert-butoxide and sodium-potassium alloy as initiators, showed spectral differences associated with the presence of another isomeric structural unit. Decreasing of the relaxation times ( T 1 ) of cis unit by increasing the concentration of this new unit was reasonably explained by assuming for this latter a trans structure linked with the cis unit to form a stereocopolymer.