Nanoscale anisotropic Orientation in Shape Memory Random POSS/Polycaprolactone Nanocomposites

Abstract

ABSTRACTShape memory nanocomposites were produced following a simple one-step synthesis route initiated by a series of molar mixtures of POSS thiol nanocages and pentaerythritol tetrakis (3mercaptopropionate), and a diacrylate polycaprolactone (PCL) with Mn=3,000 g/mol. Simultaneous wide- and small- angle X ray scattering (WAXS/SAXS), differential scanning calorimetry (DSC) and atomic force microscopy (AFM) experiments were carried out and results were correlated on microstructure. Molecular identification was performed by Fourier transformed infrared (FTIR-ATR). Thermomechanical shape memory cycles revealed that the nanocomposites achieved excellent shape recovery (99%) and shape fixity (100%) parameters. Dynamic mechanical analysis showed that elastomeric modulus decrease in function of the POSS thiol molar concentration and this result is correlated with the decrease in average crosslink density (ν). WAXS studies revealed orthorhombic crystallites for PCL combined with an amorphous POSS phase when the molar concentration of POSS was low (2.5%, 5%, 10%). However, increasing the molar concentration of POSS thiol until 20%, a broad and weak reflection centered around 2θ =7.9° which corresponded to imperfect POSS crystals. At the nanoscale, SAXS analysis showed lamellar nanostructure formation for all POSS/polycaprolactone crosslinked networks. Strikingly, induced anisotropic orientation of polycaprolactone lamellar nanostructure was observed when the concentration of POSS increased to 10 and 20 mol%.