Formation of extended ionomeric network by bulk polymerization of l,d-lactide with layered-double-hydroxide

We report the formation of an ionomeric network in a poly(l,d-lactide) hybrid nanocomposite, (PLDLA-HYB) during in-situ melt polymerization of l,d-lactide in the presence of magnesium/aluminum layered-double-hydroxide (LDH) without added catalyst.The effect of LDH mass loading and reaction time on molecular mass and yield of soluble poly(l,d-lactide) (PLDLA-SOL) present in the hybrid was investigated for a better understanding of the conflicting roles of LDH in polymerization and degradation of PLDLA-SOL. High molecular mass PLDLA-SOL is obtained through initiation of polymerization by LDH. However an additional insoluble organic-inorganic fraction, INSOL, is also observed within the product when PLDLA-SOL is extracted using methylene chloride as solvent. It is proposed that INSOL is an ionomeric network comprising hydrogen-bonded, or otherwise co-ordinated, lactic acid monomer salts of magnesium, together with PLDLA in a 24%-76% mass ratio.