Hiroko Kyotani

Synthesis of polyacetylene films with high density and high mechanical strength

Abstract We report for the first time synthesis of high density and high mechanical strength polyacetylene films. Youngs modulus and tensile strength of trans films stretched by 7 to 8 times are 100 and 0.9 GPa, respectively, comparable to those of well-known engineering plastics such as Kevlar (132 and 3.9 GPa, respectively). The films have been synthesized by using a refined non-solvent polymerization method linked with thermal treatment of catalyst solution at higher temperature. The catalyst solution was prepared by adding Ti(OBu)4 and AlEt3 into cumene solvent and subsequently it was aged at 150 °C for 3 to 5 hours. Polymerization was carried out at −78 °C under the condition where solvent was evaporated completely through dynamic pumping just before introduction of acetylene gas. The films thus prepared have not only high density of more than 1.0 g/cm3 but also high mechanical strengths. Profound potentiality of the present films was also exemplified in their electrical properties to give high conductivities of more than 2.0 × 104 S/cm upon iodine doping. Discussions have been made in terms of polymerization behavior and morphological structure essentially affecting density, drawability and mechanical strengths.

Oriented thin films of conjugated polymers : polysilanes and polyphenylenes

Abstract In this paper, preparation of uniaxially oriented films of conjugated polymers, polysilanes and poly(p-phenylenes) (PPP) is investigated. Highly oriented thin films of poly(dimethylsilane) (PDMS) were prepared by the friction transfer method. The properties of PDMS films strongly depend on the preparation temperature. At a temperature higher than 210°C, uniform ultrathin films with extremely high orientation were obtained. It is considered that the friction transfer is related to the disorder (hexagonal) phase of PDMS. Other polysilanes, such as poly(diethylsilane) (PDES), poly(di-n-hexylsilane) (PDHS), poly(di-n-butylsilane) and poly(methylphenylsilane) also afforded oriented films by the same method. Oriented films of PPP were prepared by the friction transfer method. The thin films of the polymers were characterized mainly by ultraviolet absorption spectroscopy. The friction-transferred PDMS and PPP had abilities of orienting other materials. The films of polysilanes, such as PDHS, which were cast on the oriented PDMS from solution, were oriented along the PDMS chain direction. Oriented films of some oligophenylenes were obtained by vapor deposition or cast on the friction-transferred PPP. When the friction-transferred PPP film was immersed into the reaction mixture, a newly oriented PPP film were polymerized on the friction-transferred PPP films.

Higher-order structure and thermal transition behaviour of poly(di-–hexylsilane)

Abstract Poly(di-–hexylsilane)(PDHS) films cast at various conditions from toluene solutions were studied by X-ray diffraction, d.s.c., u.v.-vis. spectroscopy and fluorescence spectroscopy. The higher-order structure of cast films is discussed in relation to their phase transitions. Films dried slowly at 2°C (film a), quickly at room temperature (film b) and slowly at 36°C (films c and d) have low, moderate and highly crystalline structures, respectively. In thin film c, the (110) plane of the orthorhombic unit cell is oriented parallel to the film surface. The u.v. absorption maxima due to the ordered phase were observed around 357 nm (film a), 370 nm (film b) and 375 nm (film c). The peaks in the fluorescence spectra were observed between 350 nm and 389 nm. The d.s.c. peak temperature for phase transition was observed at 36–49°C.

Epitaxial Growth of Polysilanes on Friction-Transferred Poly(Dimethylsilylene) Film

Abstract Highly oriented poly(dimethylsilylene) films, which were prepared by friction-transfer technique, have an ability of orienting soluble polysilanes. Solution-cast films of polysilanes on the friction-transferred film were oriented. The oriented films were characterized by polarized ultraviolet absorption spectroscopy. Several soluble polysilanes were examined and then poly(di-n-hexylsilylene) and poly(methyl-n-propylsilylene) had higher orientation. Their main chains were arranged along the main chains of the poly(dimethylsilylene).

Polyacetylene films prepared by intrinsic non-solvent polymerization method - mechanical properties and electrical conductivities

Summary form only given. We have synthesized highly stretchable and highly conducting polyacetylene films by Intrinsic Non-Solvent (INS) polymerization method and investigated the mechanical and electrical properties of the films, in order to examine the feasibility of the INS method as an advanced solvent-free polymerization method. The mechanical strengths of the films are 40 GPa in Youngs modulus and 2.1 GPa in tensile strength. The electrical conductivities upon iodine doping are 2.2 - 4.3 x 10/sub 4/ S/cm, which are enhanced by 6 - 9 fold mechanical stretching. The results imply that the present films are more easily stretchable but less breakable than the films prepared by the solvent evacuation method (Youngs modulus of 100 GPa and tensile strength of 0.9 GPa), leading to a remark that the INS method produces high quality polyacetylene films whose, mechanical and electrical properties are comparable and/or superior to those by the solvent evacuation method.

Solid state properties and thermal isomerization behavior in polyacetylene films

Summary form only given. Characterization of highly stretchable and highly conducting polyacetylene films synthesized by two kinds of solvent-free polymerization procedures, called Solvent Evacuation and Intrinsic Non-Solvent methods, have been performed with respect to the solid state properties and thermal isomerization behavior, by means of X-ray diffraction (XRD), scanning electron micrograph (SEM), and differential scanning calorimetry (DSC). We present here a deeper insight into the overall relationships between stretchability, crystallinity, and film thickness, and also a new aspect on the stepwise cis-trans isomerization mechanism. Morphological comparison has also been made by addressing traditional S-type polyacetylene films.

Dynamic Mechanical Properties of Extruded Rods of Poly(dimethylsilylene) and Polysilane Copolymers having Methyl and Ethyl Substituents

The oriented rods of poly(dimethylsilylene) (PDMS), poly(dimethylsilylene-co-methylethylsilylene) (PMMME) and poly(diethylsilylene-co-methylethylsilylene (PEEME) were prepared by extruding the polymers through a circular tube die in the temperature range where the hexagonal mesophase forms. In general PDMS cannot be processed into materials below its decomposition temperature, but it was found that PDMS could be compression molded at 250°C under nitrogen atmosphere prior to the extrusion. The extruded polysilanes were characterized in detail by dynamic viscoelasticity and wide-angle X-ray diffraction showed that the crystalline phases of PDMS, PMMME, and PEEME were transformed into the hexagonal mesophase at elevated temperatures. The dynamic storage modulus of PDMS amounts to 7.6 GPa at room temperature and 11.2 GPa at liquid nitrogen temperature. The dynamic storage modulus increases with increasing extrusion ratio, and the increase of modulus with extrusion ratio, and the increase of modulus with extrusion ratio is well correlated with the change of the crystal orientation function. The dynamic storage moduli of the extruded polysilanes were lowered with the rise in temperature owing to the structure relaxation processes, which lie in the lower temperature range. The decrease of modulus with temperature was more marked in PEEME than in PDMS, suggesting that the molecular motion of the ethyl substituents lowered the modulus at room temperature.

Polysilane Photoluminescence Specific to Oriented Thin Films

Abstract Highly oriented ultrathin films of poly (dimethylsilylene) and poly (diethylsilylene) were prepared by friction-transfer technique. Photoluminescence spectra of the films were different from those of powder sample. The luminescence peak of thin film was observed at 10nm shorter wavelength than that of powder. The difference remained from −200° C to 250° C.

Isothermal CIS-trans isomerization of polyacetylene

Summary form only given. Isothermal cis-trans isomerization behavior of polyacetylene films was carefully observed by DSC and it was found that the isomerization ratio y changes with time t by the stretched (fractional) exponential function, 1 - y = exp [ - (k/sub 0/t)/sup /spl alpha/] where k/sub 0/ and /spl alpha/ are constant and 0 < /spl alpha/ < 1. In the cis-trans isomerization, intramolecular cooperative motions of bonds and also the intermolecular cooperative motions among neighboring chains are needed in order to avoid the steric hindrance in the solid state. Intermolecular-diffusion model is proposed to simply describe the intermolecular cooperative motions of neighboring chains. Using the continuous time random walk model, the decay of survival probability of cis unit 1-y can be approximated by the stretched exponential function under the assumption of the distribution of activation energy.

Photochromic Property of Triphenylformazan Films Prepared by Vacuum Evaporation

Morphology and the photochromic property were studied comparatively for triphenylformazan (TPF) films prepared by vacuum deposition on glass substrates at -150°C (S-LT) and room temperature (S-RT). The S-LT sample showed photochromic change from violet to pale blue whereas the S-RT sample was insensitive to the irradiation of visible light. Microscopic observation indicated that rapid cooling would impede the crystallization of TPF molecules on the substrate and thereby yield amorphous films with conformational change of the molecules.