Microstructure and Phase Behavior of POSS/PCL Shape Memory Nanocomposites
(5682–5692) Macromolecules 44 #14 (2011)
Alvarado-Tenorio, Romo-Uribe, and Mather of the Universidad Nacional Autnoma de Mxico, Mexico, and Syracuse University, New York, showed that the microstructure of POSS-based networks previously reported for their shape memory properties consists of highly ordered nanoscale structures in polyhedral silsesquioxane–poly(ε-caprolactone) (POSS-PCL) semicrystalline cross-linked nanocomposites.  The oligomers used for network formation resemble a highly asymmetrical triblock copolymer featuring a single POSS moiety centered between two PCL chains, yielding two short tethers for a total molecular weight of 2600 g/mol.  Surprisingly, end-capping of the PCL alcohol groups with acrylate groups (needed for cross-linking) greatly reduced the crystalline order of POSS nanocages, whereas the orthorhombic phase of PCL remained unchanged.  Macromolecular end-linked networks showing shape memory behavior were obtained by photocuring the acrylate-terminated nanocomposites utilizing a tetrathiol cross-linker. A superstructure is present in the cross-linked networks, and the cubic superstructure is attributed to crystalline clusters formed by POSS molecules. (RDC 7/20/2011)