Osamu Haba

Head‐to‐tail regioregularity of poly(3‐hexylthiophene) in oxidative coupling polymerization with FeCl3

We investigated a head-to-tail regioregularity of poly(3-alkylthiophenes) from 3-alkylthiophene by an oxidative coupling polymerization, which is the simplest and easiest way for the synthesis of polythiophenes. The polymerizations were conducted using ferric chloride (III) as an oxidant in chloroform. Investigating the polymerization conditions, a lower temperature and a lower concentration were effective for increasing the head-to-tail (HT) content. The best HT content of 88% was obtained when the temperature was -45°C and the initial monomer concentration was 0.02 mol L -1 . Washing the resulting polymer by n-hexane further increased the content to 91%. Thus, it was found that the high regioselectivity can be achieved by the simple polymerization and the simple operation such as washing. The polymerization mechanism causing the regularity is also discussed.

Photosensitive polyimide-precursor based on polyisoimide: dimensionally stable polyimide with a low dielectric constant

Abstract A positive-working photosensitive polyimide (PI) precursor based on fluorinated polyisoimide (FPII) and 2,3,4-tris(1-oxo-2-diazonaphthoquinone-5-sulfonyloxy) benzophenone (D5SB) as a photosensitive compound has been developed. FPII was prepared by ring-opening polyaddition of dianhydrides, pyromellitic dianhydride and biphenyltetracarboxylic dianhydride, with diamine, 2,2′-bis(trifluoromethyl benzidine and followed by treatment with trifluoroacetic anhydride-triethylamine in N-methyl-2-pytrolidinone. The FPII film showed a good solubility in a wide range of organic solvents. The dissolution behaviour of FPII containing 30 wt% of D5SB after exposure was studied and it was found that the difference of dissolution rate between the exposed and the unexposed parts was enough to get a positive pattern due to photochemical reaction of D5SB in the polymer film. The photosensitive fluorinated polyimide (FPI) precursor containing 30 wt% of D5SB showed a sensitivity of 250 mJ cm−2 and a contrast of 1.5 with 436 nm light, when it was developed with a mixture of 2.38% aqueous tetramethylammonium hydroxide solution and 2-propanol at room temperature. The FPI film cured up to 360°C had a low coefficient of thermal expansion of 10.8 ppm °C−1 and a low dielectric constant of 2.89.

Synthesis of polycarbonate from dimethyl carbonate and bisphenol‐a through a non‐phosgene process

A novel nonphosgene process for producing bisphenol-A polycarbonate (PC) was developed through a transesterification between bisphenol-A (BPA) and dimethyl carbonate (DMC) and a melt-polycondensation of the resulting bisphenol-A bismethylcarbonate (1). The transesterification was carried out by heating bisphenol A in dimethylcarbonate in the presence of Lewis acid catalysts, removing the by-producing methanol using molecular shieves 4A. Among various catalysts, a combination of (Bu2SnCl)2O and dimethylaminopyridine gave the best results to produce 1 in 22% yield for 48 h. Using a larger amount of the molecular sieves further improved the yield to 80% in 120 h. The resulting 1 was heated under reduced pressure in the presence of titanium catalysts to produce PC in good yields. The resulting PC had high weight average molecular weight (Mw) of 75,000.

Measurement of nonlinear refractive index by time-resolved z-scan technique

Abstract A time-resolved z -scan technique using 100 fs laser pulses for measurement of nonlinear refractive indexes is reported. This technique allows us to measure the relaxation times of the nonlinear refractive indexes. Both the magnitude and the relaxation of nonlinear refractive indexes in CS 2 and head-to-tail poly(3-alkylthiophene) were measured. We found that there are two decay components. The slow and the fast components come from thermal effects and dielectric effects, respectively.

Synthesis of a regioregular head-to-tail poly(3-alkylphenylthiophene) by oxidative coupling using VO(acac)2

Abstract Regiocontrolled poly(3-(4-dodecylphenyl)thiophene) was prepared by oxidative coupling polymerization of 3-(4-dodecylphenyl)thiophene using an oxovanadium complex as an oxidation catalyst. Polymerizations were conducted in the presence of vanadium acetylacetonate, trifluoromethanesulfonic acid and trifluoroacetic anhydride under oxygen atmosphere in 1,2-dichloroethane at room temperature. The structure of the resulting polymer was characterized by means of 1 H- and 13 C-NMR spectroscopies, and consisted of head-to-tail linkage. Degenerate four-wave mixing (DFWM) measurements of this polymer yielded the third-order susceptibility as high as 5.1 × 10 −10 esu.

The Curing Reaction of 3-Aryl Substituted Benzoxazine

The reaction pathways on the curing reaction of 3-aryl substituted benzoxazine was investigated from the model reaction of 3, 4-dihydro-6, 8-dimethyl-3-phenyl-2H-1, 3-benzoxazine (1) with 2, 4-xylenol (2). The reaction was carried out at 140 °C for 5 h. N, N-Bis(2-hydroxy-3, 5-dimethylbenzyl)phenylamine (3) and N-(2-hydroxy-3, 5-dimethylbenzyl)phenylamine (4) were isolated as main products at an early stage. The reaction of 3 by the thermal treatment was studied by 1H-NMR spectroscopy. This result indicates that compound 3 produces several inter- and intramolecular rearrangement products. Based on these data, some possible reaction pathways were proposed. In the presence of p-toluenesulfonic acid monohydride, 3,3′-[4,4′-methylenediphenyl]bis(3,4-dihydro-6,8-dimethyl-2H-1,3-benzoxazine) (9) was isolated as one of the intermediates.

Homeotropic orientation of nematic liquid crystals induced by dissolving polypropyleneimine dendrimer having peripheral mesogens

A mixture of nematic liquid crystals (NLCs) with a small amount of a polypropyleneimine-based liquid crystalline dendrimer (D-6PC5 and D-6PPCN) exhibited spontaneous homeotropic alignment between the native glass substrates. This dendrimer-induced homeotropic alignment required two conditions; 1) the dendrimer completely dissolves in the NLC, and 2) a substrate surface is hydrophilic with the surface free energy above approximately 65 mN·m−1. The interdigitated-electrode cells without any surface treatment of the substrates were fabricated by filling with the LC dendrimer (D-6PC5)/nematic LC mixtures. They exhibited an electro-optical behavior when applying AC, vertical-alignment drive occurred in the cells. Based on these results, we speculated that the dendrimer adsorbs on the substrate surface and acts as a vertical alignment layer.

Optically driven translational and rotational motions of microrod particles in a nematic liquid crystal

Significance This paper addresses light-driven dynamic motions of microrods suspended in a liquid crystal (LC) host. The results presented in this paper advance molecular-assisted manipulations of colloidal particles and their assemblies, which is a key concept for smart microdevices, using their interplay with the topology of the nematic director field. Almost all previous studies on colloids in LC (except some work by Yamamoto et al.) have dealt with the observation and analysis of defect structures around colloid particle(s) with fixed anchoring conditions. Herein we use a photoactive surfactant, which enables control of the LC anchoring by light irradiation. The induced reversible anchoring transition is accompanied by a reorientation of the rods and/or their translational motion. A small amount of azo-dendrimer molecules dissolved in a liquid crystal enables translational and rotational motions of microrods in a liquid crystal matrix under unpolarized UV light irradiation. This motion is initiated by a light-induced trans-to-cis conformational change of the dendrimer adsorbed at the rod surface and the associated director reorientation. The bending direction of the cis conformers is not random but is selectively chosen due to the curved local director field in the vicinity of the dendrimer-coated surface. Different types of director distortions occur around the rods, depending on their orientations with respect to the nematic director field. This leads to different types of motions driven by the torques exerted on the particles by the director reorientations.

Preparation and Properties of Polyisoimides as a Highly Dimensionally Stable Polyimide Precursor with Low Dielectric Constant

Fluorinated polyimides (PIs) with low dielectric constant and high dimensional stability have been developed using polyisoimides (PIIs) as a polyimide precursor. The PIIs were prepared by the ring-opening polyaddition of the dianhydrides pyromellitic dianhydride, biphenyltetracarboxylic dianhydride and 4, 4′-hexafluoropropylidenedi(phthalic anhydride) with the diamines 2, 2′-dimethylbenzidine and 2, 2′-bis(trifluoromethyl)benzidine, followed by treatment with trifluoroacetic anhydride/triethylamine or dicyclohexylcarbodiimide in N;N-dimethylacetamide. The PIIs were soluble in a wide range of solvents including dipolar aprotic solvents, cyclohexanone and tetrahydrofuran at room temperature, and easy to convert to corresponding PIs by high thermal treatment. The resulting PIs showed low dielectric constants of less than 3 at 1 MHz as well as low CTEs. Furthermore, during the isomerization reaction, migration of copper in the PI film was hardly observed.

Optical manipulation of the nematic director field around microspheres covered with an azo-dendrimer monolayer.

We report here the optical manipulation of the director and topological defect structures of nematic liquid crystals around a silica microparticle with azobenzene-containing dendrimers (azo-dendrimers) on its surface. We successfully demonstrate the successive switching processes from hedgehog, to boojum, and further to Saturn ring configurations by ultraviolet (UV) light irradiation and termination. The switching time between these defect structures depends on the UV light intensity and attains about 50 ms. Since the pretreatment of microparticles is not necessary and the surface modification is spontaneously performed just by dissolving the azo-dendrimers in liquid crystals, this dendrimer supplies us with a variety of possible applications.