Diblock Poly(ester)-Poly(ester-ether) Copolymers: I. Synthesis, Thermal Properties, and Degradation Kinetics

Abstract

The synthesis and characterization of polycaprolactone (PCL) and poly(dioxanone-methyl dioxanone) (P(DX-co-MeDX)) block copolymers in a range of compositions of the two segments and with varying methyl dioxanone units is herein reported. The thermal properties of the copolymers were studied by differential scanning calorimetry (DSC) which revealed that copolymers exhibited two melting transitions ranging between 48 and 53 °C for the PCL segment and 71–79 °C for the P(DX-co-MeDX) segment. Copolymers exhibited only one crystallization exotherm which decreased as the MeDX content of the copolymer increased, thereby increasing miscibility of PCL and P(DX-co-MeDX) segments, a result also confirmed by scanning electron micrographs (SEM). Lastly, the kinetics of thermal degradation of PCL-b-P(DX-co-MeDX) copolymers were investigated by thermogravimetric analysis (TGA). Thermal degradation was shown to proceed in three distinct steps with the P(DX-co-MeDX) segment degrading in the first stage followed by the PCL segment in the last two stages most likely via unzipping and random polymerization mechanisms. The activation energies of copolymer degradation were determined and were found to decrease with increasing MeDX content of the copolymer. Overall, increasing MeDX content influenced both thermal properties and degradation kinetics through phase mixing of segments in the copolymers.