Castable particulate-filled epoxy resins exhibiting excellent thermal conductivity have been prepared using hexagonal boron nitride (hBN) and cubic boron nitride (cBN) as fillers. The thermal conductivity of boron nitride filled epoxy matrix composites was enhanced up to 217% through silane surface treatment of fillers and multi-modal particle size mixing (two different hBN particle sizes and one cBN particle size) prior to fabricating the composite. The measurements and interpretation of the curing kinetics of anhydride cured epoxies as continuous matrix, loaded with BN having multi-modal particle size distribution, as heat conductive fillers, are highlighted. This study evidences the importance of surface engineering and multi-modal mixing distribution applied in inorganic fillered epoxy-matrix composite.

Understanding the molecular alignment of conjugated polymers within thin‐film samples is essential for a complete picture of their optical and transport properties, and hence for the continued development of optoelectronic device applications. We report here on the efficacy of Raman anisotropy measurements as a probe of molecular orientation, presenting results for aligned polyfluorene nematic glass films. Comparison is made with the results of optical dichroism measurements performed on the same samples. We show that in many cases molecular orientation can be more directly characterized by Raman anisotropy, and that it can have a greater sensitivity to the degree of molecular orientation than conventional optical dichroism. The fact that the Raman measurements can be readily performed on the same thin films (∼ 100 nm thickness) that are required for optical dichroism means that there is no ambiguity in a direct comparison of results. This situation differs from that for standard X‐ray diffraction measurements (these require film thicknesses of several μm) and electron diffraction or electron energy loss spectroscopy measurements (these require film thicknesses of 10 nm or less). The Raman data allow the angle (relative to the chain axis) for the optical dipole transition moment to be deduced from the dichroic ratio, and confirm the role that its off‐axis component plays in limiting this ratio. The added fact that Raman anisotropy data can be collected in situ, in reflection geometry for standard device structures, and with microscopic resolution and chemical specificity makes the technique even more attractive as a non‐invasive device probe.

We report measurements of the glass transition temperature (T g ) in thin freestanding polymer films of polystyrene (PS) by means of confocal Raman spectroscopy. The paper introduces Raman spectroscopy as a novel method for the determination of T g in polymer thin films. We find excellent agreement between Raman scattering and previously reported values of T g obtained from either Brillouin scattering or ellipsometry. Further possible applications of the method to more complex conjugated polymers are briefly discussed.

Searching new shape memory polymer and the associating synthesis technology are critical on the development of smart materials. In this paper, a comprehensive study on Poly(hexylene adipate) PHA being the soft segment of shape memory polyurethane (SMPU) was presented. Bulk polymerization method was employed to synthesize the SMPU with different soft segment length (SSL) and hard segment content (HSC). The influences of SSL and HSC on its morphology and thermomechanical property using DSC, DMA, POM, and shape memory behavior were presented here. The results indicate that the thermal properties, dynamic mechanic properties, and crystal morphology of SMPU are influenced significantly by SSL and HSC. And it is found that the shape fixity increases with SSL but decreases with HSC. On the other hand, the shape recovery decreases with both SSL and HSC, and the associated recovery temperature increases either with the increasing SSL or with decreasing HSC. Lastly, it is concluded that in the PHA‐based‐SMPU, the lower limiting value of SSL for polyurethane having shape memory effect is 2000; their response temperature varied with SSL and HSC, changing from 41.0 to 51.9 °C. Stable hard segment crystal are formed at above 30% HSC sample in bulk polymerization, but shape memory behavior can also be observed when its physical crosslink point are formed in the lower HSC PHA‐based‐SMPU. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 444–454, 2007

Understanding the relationship between the number-average molecular weight (M n ) and the shape memory behavior of polymers is crucial for a complete picture of their thermomechanical properties, and hence for the development of smart materials, and, in particular, in textile technology. We report here on the study of shape memory properties as a function of M n of polymers. Shape memory polyurethanes (SMPUs) of different M n were synthesized, with various catalyst contents or molar ratio(r = NCO/OH) in the composition. In particular, two types of SMPU, namely T m and T g types according to their switch temperature type, were synthesized to compare the influence of M n on their shape memory behavior. X-ray diffraction, differential scanning calorimetry, dynamic mechanical analysis, and shape memory behavior results for the SMPUs are presented. The results indicate that the melting temperature (T m ), the glass transition temperature (T g ), the crystallinity, and the crystallizability of the soft segment in SMPUs are influenced significantly by M n , before reaching a critical limit around 200 000 g mol −1 . Characterization of the shape memory effect in PU films suggests that the T m -type films generally show higher shape fixities than the T g -type films. In addition, this shape fixity decreases with increasing M n in the T g -type SMPU, but the shape recovery increases with M n in both types of SMPU. The shape recovery temperature, in contrast, decreases with M n as suggested by the result of their thermal strain recovery. It is concluded that a higher molecular weight (M n > 200 000 g mol −1 ) is a prerequisite for SMPUs to exhibit higher shape recovery at a particular temperature.