Synthesis, characterization and biodegradability of poly(ethylene succinate)/poly(ε-caprolactone) block copolymers

In the present study, a series of poly(ethylene succinate)/poly(ε-caprolactone) block copolymers were prepared by using a two step process. In the first step, poly(ethylene succinate) (PESu) was synthesized by the melt polycondensation process while in the second, block copolymers were prepared by ring opening polymerization of ε-caprolactone (ε-CL) in the presence of stannous octoate. The copolymers were analysed with 1H NMR spectroscopy and were confirmed to possess final compositions very similar to the initial feed compositions. An increase in the ε-CL content led to an increase in the molecular weights of the copolymer, while polydispersity was narrowed. In the DSC thermographs, two melting points were recorded for copolymers containing 75 and 50 mol% PESu, confirming that block copolymers were prepared. The incorporation of ε-CL content in macromolecular chains resulted in a substantial decrease of the crystallization rates of the copolymers. PESu is a brittle material due to its low molecular weight, while the copolymer containing 75 mol% ε-CL possesses sufficient tensile strength and elongation at break. Enzymatic degradation was performed using Rhizopus delemar lipase in a buffer solution at 37 °C. Biodegradation rates were mainly affected by the crystallinity of copolymers, rather than from their molecular weight. PESu and copolymer films were degraded into very small fragments after six months soil burial while polycaprolactone remained almost unaffected.