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Crystallization studies at quiescent and shear states in isotactic polypropylene (iPP) containing nanostructured polyhedral oligomeric silsesquioxane (POSS) molecules were performed with in situ small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC). DSC was used to characterize the quiescent crystallization behavior. It was observed that the addition of POSS molecules increased the crystallization rate of iPP under both isothermal and nonisothermal conditions, which suggests that POSS crystals act as nucleating agents. Furthermore, the crystallization rate was significantly reduced at a POSS concentration of 30 wt %, which suggests a retarded growth mechanism due to the molecular dispersion of POSS in the matrix. In situ SAXS was used to study the behavior of shear-induced crystallization at temperatures of 140, 145, and 150°C in samples with POSS concentrations of 10, 20, and 30 wt %. The SAXS patterns showed scattering maxima along the shear direction, which corresponded to a lamellar structure developed perpendicularly to the flow direction. The crystallization half-time was calculated from the total scattered intensity of the SAXS image. The oriented fraction, defined as the fraction of scattered intensity from the oriented component to the total scattered intensity, was also calculated. The addition of POSS significantly increased the crystallization rate during shear compared with the rate for the neat polymer without POSS. We postulate that although POSS crystals have a limited role in shear-induced crystallization, molecularly dispersed POSS molecules behave as weak crosslinkers in polymer melts and increase the relaxation time of iPP chains after shear. Therefore, the overall orientation of the polymer chains is improved and a faster crystallization rate is obtained with the addition of POSS. Moreover, higher POSS concentrations resulted in faster crystallization rates during shear. The addition of POSS decreased the average long-period value of crystallized iPP after shear, which indicates that iPP nuclei are probably initiated in large numbers near molecularly dispersed POSS molecules.

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A unique class of polyurethane (PU) elastomer containing inorganic molecules (polyhedral oligomeric silsesquioxane, POSS) as molecular reinforcement in the hard segment was investigated by means of wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) techniques. WAXD results indicate that POSS molecules form nanoscale crystals showing distinct re¯ection peaks. The formation of POSS crystals is probably prompted by the microphase separation between solid-like hard segments and rubbery soft segments in PU. The microphase separation of hard and soft segments was observed by SAXS, which shows a long period of 111 A Ê for 34 wt% POSS-PU and 162 A Ê for 21 wt% POSS-PU, and hard segment domains with sizes of about 34 A Ê for both of them. WAXD results from a series of POSS compounds with a corner substituted by a functional group of varying length were compared with POSS-PU, which also con®rms the presence of nanoscale POSS crystals in the polymer matrix.

Segmented polyurethanes based on diphenylmethane-4,4 -diisocyanate and polytetramethylene glycol were synthesized using a mixture of polyhedral oligomeric silsesquioxane (POSS)-diol and 1,4-butanediol as chain extenders. The polymers were characterized by differential scanning calorimetry, wide-angle x-ray diffraction (WAXD), small-angle x-ray scattering (SAXS) and tensile property tests. Microphase separation between the hard and soft segment domains was observed in all the samples by SAXS. The increase of the POSS concentration was found to weaken the microphase separation between the domains and increase the T g of the soft segments. The WAXD results showed that when the POSS concentration was greater than 10 wt%, the 101 diffraction peak from the POSS crystals could be observed, which suggested the formation of POSS nanocrystals in the hard domain. The tensile property tests showed that polyurethanes containing the nanostructured POSS molecules had higher moduli, but lower maximum elongation ratios.

A novel hybrid organic/inorganic triblock copolymer of polystyrene-butadiene-polystyrene (SBS) containing grafted polyhedral oligomeric silsesquioxane (POSS) molecules was synthesized by a hydrosilation method. The POSS molecules were designed to contain a single silane functional group, which was used to graft onto the dangling 1,2-butadienes in the polybutadiene soft block. Unlike typical free radical copolymerizations commonly used for many other POSS incorporations investigated, this synthesis method allows us to make a series of polymers with varying amounts of POSS without any change to the overall degree of polymerization or structure of the main SBS backbone. This gives us a unique opportunity to study the POSS behavior in the matrix and know that all differences are solely due to the POSS grafted to the soft continuous butadiene phase. X-ray diffraction revealed that the grafted POSS are very well dispersed in the matrix of the hybrid polymer, which is compared to the strong phase segregation observed in a POSS physical blend. Small-angle X-ray scattering indicates that although the cylindrical morphology attributed to the styrene component was not altered by the presence of POSS, attachment of POSS to the continuous phase (polybutadiene block) causes the packing of discrete phase (polystyrene blocks) to lack long-range features. Results of dynamic mechanical analysis showed that the POSS has sterically hindered the motion of the polybutadiene blocks. More interestingly, the presence of POSS in the soft segments also resulted in a tapered tan δ peak associated with the glass transition of polystyrene and a higher tensile strength when deformed at temperature near T g of polystyrene without affecting the elongational behavior of SBS at temperatures above Tg of polybutadiene.