Toshio Yoshikawa

Structural change of a polymeric hindered amine light stabilizer in polypropylene during UV-irradiation studied by reactive thermal desorption-gas chromatography

Abstract The structural changes of a polymeric hindered amine light stabilizer (HALS), Adekastab LA-68LD (MW=1900) added in PP materials during UV-irradiation were investigated by reactive thermal desorption-gas chromatography (RTD-GC) in the presence of tetramethylammonium hydroxide [(CH3)4NOH, TMAH]. Not only the products formed from the residual intact HALS, but also those from its oxidized moiety (nitroxyl radical) were observed on the resulting chromatograms without the use of any troublesome sample pretreatment such as solvent extraction. The changes in the yields of these key products were then examined as a function of UV-exposure time. As a result, it was revealed that the amount of the nitroxyl radical increased in the initial stage of UV-irradiation but then slightly decreased mainly because of further decomposition into the smaller compounds, whereas that of the intact HALS monotonously decreased during exposure.

Highly sensitive determination of a polymeric hindered amine light stabilizer in polypropylene by reactive thermal desorption–gas chromatography using nitrogen-specific detection

Highly sensitive and specific determination of trace amounts of a polymeric hindered amine light stabilizer (HALS) in polypropylene (PP) materials could be established by improving reactive thermal desorption-gas chromatography (RTD-GC) in the presence of an organic alkali, tetramethylammonium hydroxide. By using nitrogen-phosphorus detection, highly selective detection of the HALS-related components was attained. In addition, the use of a polar poly(ethylene glycol) separation column alleviated the adsorption of minor specific pyrolysis products. This modified RTD-GC method allowed the determination of the polymeric HALS (Mr 1900) in PP even for trace concentrations between 100 and 500 ppm, through observing selectively the characteristic products containing a tetramethylpiperidine moiety, which had been impossible to detect under the previous RTD-GC conditions using a non-polar separation column and conventional flame ionization detection.

Molecular Organization of Nonlinear Organic Films Laminated by Langmuir-Blodgett Method

In the 21st century, the optical computation is likely to be the basic technology for processing lots of information at high speed. The aim of the present research work is to develop optical logic gates or memory chips. For this purpose, we have examined the suitability of organic nonlinear optical dye material Vanadyl-phthalocyanine (VOPc). Large single crystals of this material have been fabricated by using Molecular Beam Epitaxy (MBE) technique. The epitaxial films were formed on the substrate under optimum operating conditions. However, the epitixial growth is observed only up to a limited thickness. Above this thickness, the films become non-epitaxial, which can be improved by annealing. The reformation of the epitaxial films has been confirmed. We have also reported the effects of the environment of high temperature on the multilayered tetra-tert-butyl-Vanadyl-phthalocyanine ((t-bu)4VOPc) films, formed by Langmuir-Blodgett (LB) method. The solvent used to dissolve ((t-bu)4VOPc) was 1,2-dichloroethane. The monolayer on the surface of the water was transferred to a glass substrate by the vertical dipping method. If the multilayered stack is too thick, the molecular arrangement of the film may get disturbed. The improvement in the molecular arrangement of the LB films was examined and confirmed by measuring it’s nonlinear optical susceptibility, using Maker Fringe Method. Monolayer formation on water surface depends on the surface pressure-area isotherm. If this monolayer formation is not perfect, multiplayer stacks cannot be formed. The molecular films were aligned almost perpendicular to the substrate, as estimated from the limiting molecular area of surface pressure-area isotherm. The molecular organization of the monolayer on the substrate and the molecular structure of the multilayered ((t-bu)4VOPc) films are discussed.

Effects of corona charging on nonlinear optical property and morphology of VOPc thin film prepared on polyimide substrate by molecular beam epitaxy

One important factor for a nonlinear optical thin film having high second and third nonlinear optical susceptibilities is a high packing density. Vanadyl-phthalocyanine (VOPc) thin films were prepared on non-charged and corona-charged polyimide substrates by the molecular beam epitaxy (MBE). The Vis/UV spectrum of Sample 1on a non-charged substrate had a maximum absorption peak at 835 nm. According to Griffiths et al., the VOPc thin film has a maximum absorption peak at 830 nm, after prepared on a glass at room temperature and heated at 325/spl deg/C for 2 hours. He called the morphology of Phase III. The maximum absorption peak of Sample 1 shifted longer by 5 nm than that reported by Griffiths. This means that the packing density of Sample 1 is higher than that of the VOPc thin film reported by Griffiths. A maximum absorption peak in Q band region of Sample 4 on a corona charged substrate appeared at 845 nm, which is longer by 10 nm than that of Sample 1. This suggests that a strong interaction between VOPc molecule and electric charge on polyimide substrate makes a high molecular packing of Sample 4. The third harmonic (TH) generations of Samples 1 and 4 were measured by Maker fringe with P polarized laser light. The peak value of TH intensity of Sample 4 was larger by 2 times than that of Sample 1. This means that the nonlinear optical property of VOPc thin film is improved by corona charging.

Nonlinear optical properties and morphologies of vanadyl-phthalocyanine crystal prepared on KCl substrate

Vanadyl-phthalaocyanine (VOPc) films were prepared on KCI substrate by a molecular beam epitaxy (MBE) method. The SEM image revealed that a VOPc single crystal of 120)mumX120)mum grew on the KCI substrate after annealiing for 360 minutes. Its average film thickness was about 110 nm. The growth of single crystal was assisted by the surface diffusion of VOPc molecules and the difference in chemical potential between single crystals. Therefore, the single crystal grows merging neighboring grains and/or VOPc molecules surrounding. The VIS/UV spectrum of single crystal had the absorption peaks at 700nm and 860nm and also the absorption shoulder at 640nm. The maximum absorption peak is at 860nm. According to Griffiths et al., the phase having peaks at 680nm and 740nm is called Phase I and the phases having a main absorption peaks at 820nm and 830nm are called Phase II and Phase III, respectively. Phases having a main absorption peaks at 780nm and 810nm are called Pseudomorphic layer and epitaxial growth, respectively. As mentioned above, the phase having a main absorption peak at 860nm has not been reported so far. We call it Phase IV. The VOPc film having Phase IV shows a third harmonic (TH) generation. The TH susceptibility is larger by about 103 times than that of quartz glass. This indicates that Phase IV has high molecular packing density and good nonlinear optical properties. Therefore the single crystal on KCI substrate prepared by MBE is expected to apply to optical switching, modulation and memory (RAM and ROM).

Orientation of vanadyl-phthalocyanine film prepared by molecular beam epitaxy and treated in organic gas

In this paper, the VOPc film was prepared on KBr substrate by OMBD. After that, it was treated in organic gas. The thickness of VOPc film was 96 nm. The morphologies of VOPc film before and after the gas treatment were characterized with optical absorption spectra and SEM image. The third- harmonic generation of VOPc film before and after the gas treatment were also measured by Maker fringe method using a Nd:YAG laser.

Third harmonic generation of soluble vanadyl-phthalocyanine doped in polymer film

The third-order optical susceptibilities of PMMA thin films doped with soluble vanadyl-phthalocyanine derivatives ((t-Bu)/sub n/VOPc) were studied by Maker fringe method. We intended to control the molecular packing of VOPc in PMMA in order to improve third-order optical susceptibility (/spl chi//sup (3)/). For this purpose we selected soluble /sub n/VOPc derivatives and obtained a packing structure similar to the phase II of VOPc thin film. Packing control of the phthalocyanine molecules was carried out by exposing PMMA films to organic solvent vapour. PMMA thin films doped with (t-Bu)/sub 4/VOPc, (t-Bu)/sub 1.45/VOPc and (t-Bu)/sub 1.44/VOPc were treated with dichloroethane vapour in a desiccator at room temperature. The intensity of THG are in the order of (t-Bu)/sub 1.45/VOfc/PMMA>(t-Bu)/sub 1.44/VOPc/PMMA>VOPc(t-Bu)/sub 4/VOPc/PMMA. This means that the hyperpolarisability of (t-Bu)/sub n/VOPc molecule depends upon a number of tert-butyl radicals. The third-order optical susceptibility (/spl chi//sup (3)/) was estimated for (t-Bu)/sub 1.45/VOPc/PMMA. Its value was about 7/spl times/10/sup -12/ esu. This technique is useful to make optical waveguide.

Second- and third-harmonic generations of soluble vanadyl phthalocyanine doped in polymer films

PMMA and PET thin films doped with (t-Bu)4VOPc {(t- Bu)4VOPc PMMA and (t-Bu)4VOPc PET} and PMMA thin film doped with (t-bu)1. 4VOPc {(t-Bu)1. 4 VOPc PMMA} were prepared on glass substrate by coating (t-Bu)4VOPc PMMA and (t-Bu)4VOPcPET were treated with dichloroethane vapor in a desiccator at room temperature. On the other hand, (t-Bu)1. 4VOPc PMMA was treated with dichloroethane and chloroform vapor in the desiccator at room temperature. The (t-Bu)1. 4VOPc PMMA and (t-Bu)4VOPc PMMA thin films showed SHG and THG after vapor treatment but (t-Bu)4VOPc PET thin film did not. These suggest that the degree of swelling by dichloroethane vapor are different between PMMA and PET. In other words, the aggregation of (t-Bu4) VOPc occurs more easily in PMMA than in PET. The THG of (t-Bu)1. 4VOPc PMMA thin film is larger than that of a (t-Bu)4VOPc PMMA thin film. This means that the molecular size of (t-Bu)1. 4VOPc is smaller than that of the size of (t-Bu)4VOPc.

TSC study of phase transition of vanadyl phthalocyanine thin film produced on glass by molecular beam epitaxy technique

Vanadyl phthalocyanine (VOPc) films were produced on glass substrates by the MBE technique. Films produced at a substrate temperature of room temperature have a phase I, which displays absorption peaks at 680 nm and 740 nm in UV-visible spectroscopy. The red-shifted phase introduced by heating at 100/spl deg/C for one hour is called phase II. We investigated the phase transition process from phase I to phase II with the TSC method. The TSCs of VOPc/glass measured under a poling temperature of 100/spl deg/C and poling voltage of 600 V have three peaks. Two peaks are related to the glass substrates. The remaining peak near -30/spl deg/C is related to the VOPc film. A polarization of the film is suggested to occur in the phase I to II transition region. The force between molecules is a Van der Waals force so that the depolarization in the phase transition is suggested to be below room temperature. Therefore, the peak is concluded to be due to the phase transition process of VOPc thin film.