Novel poly(ester-urethane)s based on polylactide: From reactive extrusion to crystallization and thermal properties

The synthesis of novel poly(ester-urethane)s (PEUs) based on polylactide was carried out. It was performed by a catalysed two-step reaction process, i.e., ring-opening polymerization (ROP) and chain extension reaction in bulk. For this purpose, α,ω-dihydroxyl PLA macrodiols were synthesized by catalysed ROP and employed as precursors that reacted in the melt with 4,4′-diisophenylmethane diisocyanate (MDI) and 4,4′-diaminodiphenylmethane (MDA) as coupling agent and chain extender, respectively. The PEUs were characterized by DSC, Polarized Light Optical Microscopy and X-ray techniques. The PEUs were generally characterized by higher cold crystallization temperature, lower melting temperature and slower cold crystallization kinetics as compared to the PLA precursors. The Avrami equation modelled the entire isothermal cold crystallization process. The synthesis variables that had the largest impact on the crystallization and thermal properties of the PEUs were the molecular weight of the PLA precursors and the [NCO]/[OHPLA + NH2] ratio, which could be readily tailored by the investigated reactive melt-processing.