Kenichi Hayashida

Flame retardant mechanism of polydimethylsiloxane material containing platinum compound studied by analytical pyrolysis techniques and alkaline hydrolysis gas chromatography

Abstract The flame retardant mechanism for silicone rubber induced by adding ppm order of a platinum compound, platinum (0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex was studied by analytical pyrolysis techniques and alkaline hydrolysis gas chromatography. The thermal degradation measurement of the flame retardant silicone rubber sample (FR-SR) indicated that a considerable amount of methane was evolved from the FR-SR sample at around 400–800 °C while formations of cyclic siloxanes were fairly suppressed in comparison with that from the control SR sample. On the other hand, on the gas chromatogram of the hydrolysis products from the FR-SR residue samples thermally treated over 400 °C, significant amounts of characteristic products reflecting the cross-linking structures generating from methylene-bridge and trifunctional siloxane structures in the polymer chains were observed. These results suggest that the thermal decomposition of the FR-SR material is strongly suppressed by the formation of the cross-linking structures induced by the platinum compound during combustion, which leads to its flame retardancy.

Jewelry Box of Morphologies with Mesoscopic Length Scales – ABC Star-shaped Terpolymers

Among several star molecules studied so far, the results for two similar but slightly different systems composed of all hydrophobic components, i.e. one low T(g) arm and two high T(g) arms were compared and discussed mainly. They are polyisoprene-arm-polystyrene-arm-poly(2-vinylpyridine) stars and polystyrene-arm-polybutadiene-arm-poly(2-vinylpyridine) ones, and are abbreviated as ISP and SBV, respectively, in the original literatures. Several periodic Archimedean tiling patterns can be naturally formed when the relative lengths of three chains are similar one another in both series. Core-shell type morphologies and actually three-phase four layer lamellar structures were also commonly observed for two series. A quasicrystalline tiling with dodecagonal symmetry can also be conformed at the targeted composition of ISP/homopolymer blend and a zinc-blende type structure was created at just a little outside of tiling region for the same blend. Furthermore, the several interesting structures from amphiphilic molecules, composed of a hydrophilic component, poly(ethylene oxide), a hydrophobic component, polymethylmethacrylate and a highly water-repellent polymer poly(perfluoropropyleneoxide) are described and introduced.

Dielectric properties of polymethacrylate-grafted carbon nanotube composites

The dielectric properties of a series of multi-walled carbon nanotubes on which poly(cyclohexyl methacrylate)s were densely grafted (PCHMA-CNTs) were systematically characterized over the broad frequency range of 10−2–108 Hz. PCHMA-CNT was used as an ideal polymer/CNT nanocomposite system in which the CNT is homogeneously dispersed and the polymer/CNT interface is strong. When the volume fraction of the CNT ΦCNT 0.1 a very large e′r was observed at low frequencies. The Cole–Cole relaxation model was applied to the impedance spectra of PCHMA-CNT in order to investigate the correlation between the tunneling conduction and the very large e′r. Also, from thus-obtained relaxation frequencies, the inter-nanotube distance in the PCHMA-CNT system was estimated. As a result, a new mechanism was proposed for the very large e′r: the locally enhanced electric field by the tunneling conduction results in the very large e′r at the low frequencies along with the increase in e′′r. Furthermore, the CNT was demonstrated to be five times more effective than barium titanate (BT) for the enhancement in e′r of polymer materials because of the higher electric field enhancement effect of the CNT than that of the BT.

Kaleidoscopic morphologies from ABC star-shaped terpolymers

Star-shaped terpolymers of the ABC type composed of incompatible polymer components give a variety of ordered structures with mesoscopic length scales depending on their composition ratio. Their peculiar features are summarized in this report. Polymer components adopted are polyisoprene (I), polystyrene (S) and poly(2-vinylpyridine) (P), and many monodisperse samples of the I(X)S(Y)P(Z) type were anionically prepared. Firstly our focus is on molecules of the I(1.0)S(1.0)P(x(1)) type, where x(1) is only a variable. The complex but systematic morphology change was displayed within the range 0.2 ≤ x(1) ≤ 10, that is, their structures change from spherical plus lamellae structure for I(1.0)S(1.0)P(0.2) to periodic tilings (0.4 ≤ x(1) ≤ 1.9), then to lamellae-in-lamella (3.0 ≤ x(1) ≤ 4.9) and lamellae-in-cylinder (7.9 ≤ x(1) ≤ 10) structures with increasing x(1). Here if we pay attention to the structural variation of the P domain inclusively, it transforms from sphere to cylinder, lamella and then to matrix, which is the same as that for linear polymers. Among them, several periodic Archimedean tiling patterns can be naturally formed when the relative lengths of the three chains are close to one another. Moreover, it has been found that the tiling zone is spread out widely. For example, the series I(1.0)S(1.8)P(x(2)) (with 0.8 ≤ x(2) ≤ 2.9) and the other series I(1.0)S(y)P(2.0) (with 1.1 ≤ y ≤ 2.7) show mostly Archimedean tilings. Additionally, block copolymer/homopolymer blends with a composition of I(1.0)S(2.7)P(2.5) reveal a quasicrystalline tiling with dodecagonal symmetry. Furthermore, a zinc-blende-type four-branched network structure was created just a little outside of the tiling region for a block copolymer/homopolymer blend of I(1.0)S(2.3)P(0.8). When some more asymmetry in chain length is introduced, hyperbolic tiling on a gyroid membrane has successfully been constructed for the sample I(1.0)S(1.8)P(3.2) and it transforms into a hierarchical cylinders-in-lamella structure with further increase in P content to I(1.0)S(1.8)P(6.4). Thus, kaleidoscopic morphologies have been generated from ABC star-shaped terpolymers and their structural change has turned out to be very sensitive to relative compositions.

An ideal nanostructure of polymer/BaTiO3 dielectric materials with high reliability for breakdown strength: isolated and uniformly dispersed BaTiO3 nanoparticles by thick polymer shells

Poly(methyl methacrylate)s (PMMAs) with various chain lengths were grafted onto barium titanate (BT) particles using surface-initiated polymerization. The obtained core–shell particles were blended with additional PMMA to yield nanocomposites where the BT particles could not approach each other due to the PMMA shells (PMMA-BT). It was confirmed that the BT particles were uniformly dispersed in PMMA-BT by SEM observation. Reliability of the dielectric properties of PMMA-BT was evaluated under an alternating current electric field at 50 Hz using 16 specimens, and compared to that of conventional nanocomposites prepared by blending PMMA with the unmodified BT nanoparticles. The homogeneous distribution of the BT particles for PMMA-BT had no great influence on the reliability of complex relative permittivity while it improved the reliability for the dielectric breakdown strength EDB. The superior reliability for the EDB of PMMA-BT would result from the absence of percolation of the BT particles in the PMMA-BT system. This finding demonstrates that the nanostructure where the BT particles are isolated and uniformly dispersed by polymer shells is ideal for high EDB reliability.

Poly(methyl methacrylate)-grafted ZnO nanocomposites with variable dielectric constants by UV light irradiation

A series of poly(methyl methacrylate)-grafted ZnO nanoparticles (PMMA–ZnO) were synthesized using a surface-initiated polymerization technique and the optical and dielectric properties of PMMA–ZnO were studied. The dielectric constant er′ of PMMA–ZnO thin films was highly increased by irradiation of UV light. It is indicated that electrons in the ZnO nanoparticles are excited from a valence band to a conductive band by absorption of UV light, resulting in a large increase in er′ owing to Maxwell–Wagner polarization of the resultant free electrons. On the other hand, the dissipation factor (tanδ) of PMMA–ZnO is very low and almost constant during UV irradiation because PMMA–ZnO is electrically insulated by the grafted PMMA chains on the ZnO nanoparticles. Also, it was confirmed that due to the grafted PMMA chains, PMMA–ZnO nanocomposites exhibited low light scattering in addition to strong absorption of UV light. The low light scattering of PMMA–ZnO would enhance the absorption efficiency of UV light and therefore contribute to the large increase in er′ for PMMA–ZnO. Thus, PMMA–ZnO is a promising material for high sensitivity and low loss UV light sensors using the change in er′.

Highly improved dielectric properties of polymer/α-Fe2O3 composites at elevated temperatures

α-Fe2O3 particles were incorporated into ten kinds of polymer matrices, and the dielectric properties of the resultant polymer/α-Fe2O3 composites were investigated between 40 °C and 160 °C. We found that the dielectric properties strongly depended not only on the temperatures but also on the kind of polymer matrices. For engineering plastics such as polyetherimide (PEI), the dielectric constant e′r was highly enhanced at around 1 kHz by incorporation of the α-Fe2O3 particles owing to Maxwell–Wagner polarization of free electrons in the α-Fe2O3 particles. This is probably because the π electrons in the aromatic structures of the engineering plastics strongly interact with the electrons in the α-Fe2O3 particles. Furthermore, the dielectric loss factor e′′r for the engineering plastics became small at elevated temperatures because the conductivity of the α-Fe2O3 particle was enhanced and therefore the relaxation frequency of Maxwell–Wagner polarization was shifted to higher frequency. PEI/α-Fe2O3 composites exhibited highly improved dielectric properties at around 1 kHz, the high e′r and very low e′′r at the elevated temperatures above 120 °C. It was demonstrated that the PEI/α-Fe2O3 composite was comparable to the PEI/BaTiO3 composite in dielectric performance at 160 °C. Because the cost of α-Fe2O3 is much lower than that of BaTiO3, the PEI/α-Fe2O3 composite might be promising as a low-cost dielectric material for high-temperature applications.