SYNTHESIS AND CHARACTERIZATION OF BIODEGRADABLE HOMOPOLYMERS AND BLOCK-COPOLYMERS BASED ON 1,5-DIOXEPAN-2-ONE

Homopolymers of 1,5-dioxepan-2-one (DXO) and block copolymers of DXO a nd epsilon-caprolactone (epsilon-CL) have been synthesized with alumin um isopropoxide as an initiator in toluene and tetrahydrofuran (THF). The homopolymerization is first order with respect to both monomer and initiator, and the end-group analysis agrees with a coordination inse rtion mechanism based on the acyl-oxygen cleavage of the DXO ring. Liv ing poly(epsilon-caprolactone) (PCL) and poly(1,5-dioxepan-2-one) (PDX O) chains are very efficient macroinitiators for the polymerization of DXO and epsilon-CL, respectively, with formation of block copolymers of a narrow molecular weight distribution. Size-exclusion chromatograp hy (SEC) and C-13 NMR confirm the blocky structure of the copolymers, in agreement with DSC that show a melting endotherm for the PCL block and two glass transitions characteristic of the amorphous phases of PD XO and PCL. Because of the crystallinity of the PCL block (T(m) = 60-d egrees-C) and the low glass transition temperature of the amorphous PD XO block (T(g) = -39-degrees-C), poly(epsilon-CL-b-DXO-b-epsilon-CL) t riblocks have the potential of thermoplastic elastomers. Block copolym ers of epsilon-CL and DXO are also sensitive to hydrolysis which makes them possible candidates for biomedical applications. Initiation of t he DXO polymerization with functional diethylaluminum alkoxides is als o discussed.