SYNTHESIS AND CHARACTERIZATION OF A NEW DEGRADABLE THERMOPLASTIC ELASTOMER BASED ON 1,5-DIOXEPAN-2-ONE AND EPSILON-CAPROLACTONE

A new, highly elastomeric ABA triblock copolymer made from epsilon-cap rolactone (epsilon-CL) and 1,5-dioxepan-2-one (DXO) has been synthesiz ed by sequential addition of the comonomers in THF or toluene solution initiated by aluminum isopropoxide. Careful purification of the comon omers was essential to obtain high conversion of the final amount of t he added monomer. The optimal conditions were found to be polymerizati on in toluene solution at 25 degrees C with the addition of 1 molar eq uivalent (with respect to initiator) of pyridine, which gives a slight increase in the rate of polymerization. Under these conditions, poly( epsilon-CL-b-DXO-b-epsilon-CL) triblock copolymers of high molecular w eight (M(n) > 10(5) g/mol) with a relatively narrow molecular weight d istribution were obtained. Thermal analysis shows a melting peak at 51 degrees C and a glass transition at ca. -38 degrees C, corresponding to the PCL block crystalline phase and the PDXO amorphous region, resp ectively. The mechanical properties of these materials are highly elas tic and can be varied by tailoring the block lengths of the correspond ing comonomers. Tensile modulus, tensile strength at break, and elonga tion at break were found to be 20-30 MPa, 50 MPa, and ca. 1000%, respe ctively. (C) 1995 John Wiley & Sons, Inc.