The microstructure and shape-memory properties of norbornyl±POSS hybrid copolymers having either cyclohexyl corner groups (CyPOSS) or cyclopentyl corner groups (CpPOSS) were investigated by transmission electron microscopy and thermomechanical analysis. Here, POSS refers to the polyhedral oligomeric silsesquioxane macromer. Samples containing 50 wt% of POSS macromer have been mechanically drawn at temperatures above their glass transition temperatures, followed by rapid quenching in LN 2 . Shape-memory properties of such drawn samples were explored by measuring recovered strain while heating above the T g using thermomechanical analysis. Incorporation of POSS comonomers within PN is found to slightly reduce the percentage recovery, while improving thermal stability signi®cantly. Interestingly, the types of corner groups in the POSS macromer affect the shape-memory behaviour, with the CyPOSS copolymer showing lower percentage recovery than the CpPOSS copolymer due to enhanced aggregation of CyPOSS macromers. # 2000 Society of Chemical Industry Keywords: shape-memory polymer; POSS; polynorbornene; nanocomposite. INTRODUCTIONShape memory refers to the ability of certain materials to remember a shape, on demand, even after rather severe deformations. The most common material exhibiting such a property is nitanol, a nickel±titanium alloy the shape-memory effect of which is produced by a solidstate phase transformation.1 In recent years, shapememory polymers have received increasing attention because of their low cost, low density, high shape recoverability and easy processability, compared to conventional shape-memory alloys.2±4 Basic principles of the shape-memory effect in polymeric materials can be well described by their elastic modulus±temperature behaviour. At temperatures above the glass transition temperature (T g ), the polymer achieves a rubbery elastic state where it can be easily deformed without stress relaxation by applying external forces over a time-frame t ( t, where t is a characteristic relaxation time. When the material is cooled below its T g , the deformation is ®xed and the deformed shape remains stable. The predeformation shape can be easily recovered by reheating the material to a temperature higher than the T g . Therefore, admirable shape-memory behaviour requires a sharp transition from glassy state to rubbery state, a long relaxation time, and a high ratio of glassy modulus to rubbery modulus.
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