Synthesis and characterization of ω-pentadecalactone-co-ε-decalactone copolymers: Evaluation of thermal, mechanical and biodegradation properties

Abstract

ε-Decalactone (ε-DL), whose homopolymer is completely amorphous owing to the racemic stereochemistry of its butyl side chain, was copolymerized with ω-pentadecalactone (ω-PDL) in order to reduce the high crystallization capability of the latter. NMR characterization showed that the poly(ω-PDL-co-ε-DL), with ω-PDL molar contents ranging from 30 to 78%, presented a blocky chain microstructure (randomness character R < 0.49). ω-PDL homopolymer (PPDL), with a Tm at 104 °C and a Tg at ∼ −36 °C, exhibited a degree of crystallinity of 54% and the incorporation of ε-DL decreased its crystalline fraction to 13–38% and the Tg to around −50 °C. As a result, these copolymers displayed high elongation at break values and lower stiffness than PPDL (with secant modulus of 7–156 MPa) while their mechanical properties remained constant at 37 °C. The poly(ω-PDL-co-ε-DL), with a melting enthalpy in the range of between 36 and 106 Jg−1, presented a melting temperature higher than 69 °C and showed great thermal stability, degrading at temperatures higher than 400 °C. However, in vitro degradation studies during 182 days demonstrated that, despite their increased amorphous character, these materials were very resistant to hydrolysis due to the steric effect of the ε-DL units, and can virtually be considered as non-biodegradable polymers.