MACROMOLECULAR ENGINEERING OF POLYLACTONES AND POLYLACTIDES .13. SYNTHESIS OF TELECHELIC POLYESTERS BY COUPLING REACTIONS

Aromatic diisocyanates, such as phenylene-1,4-diisocyanate have proved to be very effective coupling agents of alpha-X functional omega-hydroxy poly-epsilon-caprolactone (PCL). Very high yields (>98%) have been observed in the presence of triethylamine, in tetrahydrofuran. Accordingly alpha,omega-X functional PCL of a two-fold molecular weight have been obtained and characterized by size exclusion chromatography and nuclear magnetic resonance spectroscopy. More interestingly, the same coupling reactions have been successfully carried out when applied to the precursor living polyester (X-CH2-O-PCL-O-AlEt(2)) rather than to the chains recovered after hydrolysis of the living propagating sites. Terephthalic acid chloride has been the most efficient coupling agent and, in the presence of pyridine, has yielded quantitatively the expected alpha,omega-functional polyesters.