Dynamic Mechanical Behavior of Photo-Cross-linked Shape-Memory Elastomers
(5336–5343) Macromolecules 44 #13 (2011)
Li et al of the University of Rochester, New York, incorporated photo-cross-linkable benzophenone side groups were incorporated into linear macromers containing reversible (2-ureido-4-pyrimidinone, UPy) side groups.  This method enables melt-processing of shape-memory elastomers into complex permanent shapes, and samples can be prepared with much higher UPy-content. UV–vis spectroscopy was applied to study the efficacy of the cross-linking process.  Resulting elastomer networks with variable densities of covalent cross-links and reversibly associating side groups were systematically prepared and studied.  Dynamic mechanical analysis revealed the presence of two storage modulus plateaus: a high-temperature plateau attributed to covalent cross-links, and a lower temperature plateau attributed to both reversible and covalent cross-links.  Results also show that dynamic cross-links behave nearly as effectively as permanent cross-links below the UPy hydrogen bond transition and that the presence of a covalent network supports cooperative binding of UPy side groups.  (RDC 7/6/2011)