Physical properties and biodegradation of poly(butylene adipate)ionomers

Abstract

Rapidly biodegradable and feasible poly(butylene adipate) ionomers (PBAi) were synthesized using dimethyl 5-sulfoisophthalate sodium salt (DMSI) up to 5 mol% of diacid monomer. Spectroscopically determined ionic contents of the polymers corresponded well to the feed compositions. Melt rheology experiments displayed the relaxation of ion clusters in PBA ionomers containing 3–5 mol% DMSI over the temperature range of 150–200 °C. The melting point depression in the ionomers was less than 1 K per mol% of DMSI, comparable to the most aliphatic co-polyesters. On the other hand, substantial decrease in enthalpy of fusion was observed at 3–5 mol% of ion content, indicating that crystallization is seriously retarded by the ionic interaction. It was found that PBA ionomers, despite the low molecular weight, exhibited acceptable tensile properties ascribable to chain extension effect due to the ionic interactions. Most importantly, the hydrolytic degradation of the ionomers was drastically accelerated compared to PBA homopolymer because the presence of ionic moieties reduced the crystallinity and allowed easier moisture penetration, and thus improved hydrolytic susceptibility.