Characterization of the cross-linked structure of fumarate-based degradable polymer networks

A new method was developed to examine networks formed with linear macromers of fumaric acid and diacrylate cross-linking agents in order to analyze their cross-linked structure. This method involved the accelerated degradation of the networks and the analysis of the degradation products. Two model networks of poly(propylene fumarate) (PPF) cross-linked with poly(propylene fumarate)-diacrylate (PPF-DA) and oligo(poly(ethylene glycol) fumarate) (OPF) cross-linked with poly(ethylene glycol)-diacrylate (PEG-DA) were evaluated with this method to determine the macromer and cross-linking agent conversions, the network cross-linking density, and an estimate of the molecular weight between cross-links. The validity of the method was confirmed by the analysis of the composition of the un-cross-linked macromers and the correlation of the mechanical properties of the cross-linked polymers with the macromer/cross-linking agent double bond ratio. The results showed that acrylate species had participated more than fumarates in network formation. Furthermore, the structure of PPF/PPF-DA networks was influenced by the amount of cross-linking agent in the polymer formulation, and the OPF/PEG-DA network structure was controlled by the number of repeating fumarate units in the macromer. This method provides a new means to characterize the macromolecular structure of fumarate-based networks.