Biodegradable Shape-Memory Polymer Networks: Characterization with Solid-State NMR

Abstract

Polymer networks made from oligo[(L-lactide-ran-glycolide)]dimethacrylates by UV curing are characterized by solid-state NMR. These polymer networks show a shape-memory effect and could be used as temporary implant materials for medical applications. The 13C spectra enable the direct determination of the cross-link density by a signal at 44 ppm. This is used to correlate its intensity with the chain segment length as well as to study the kinetics of photo-cross-linking. The latter is compared with the gel content, and it is found that the NMR method detects the real amount of covalent cross-links whereas the gel content also depends on influences from constraints such as physical entanglements. The shape-memory effect of the polymer networks can be followed as well by 1H double quantum buildup curves of samples that are programmed by stretching. Results indicate the reversibility of the shape-memory process.