Characterization of chemical structure and morphology of eroding polyanhydride copolymers by liquid-state and solid-state 1 H n.m.r.

An n.m.r. investigation of the chemical and morphological changes occurring during erosion in pH 7.4 phosphate buffer at 37°C of melt-fabricated polyanhydride devices formed from copolymers of 1,3-bis(p-carboxyphenoxy)propane (CPP) and sebacic acid (SA) is reported. From sequence distributions determined using solution-state Full-size image (<1 K) n.m.r. spectroscopy, the following order of anhydride bond lability was determined: SA–SA≈SA–CPP≫CPP–CPP, leading to preferential hydrolysis of aliphatic blocks within the copolymer chain. Solid-state Full-size image (<1 K) and Full-size image (<1 K) n.m.r. spectroscopy were used to investigate morphological changes occurring during erosion. Both indicated significant absorption of mobile water after ca. 10 h. Subtle variations in the symmetry of the narrow signals confirmed the changes in chemical composition apparent from high resolution Full-size image (<1 K) n.m.r. analysis. In the initial stages, there was an increase in crystallinity attributed to preferential erosion of amorphous regions.