Poly vinyl carbazole

However, the discovery that exposure to light could increase substantially the electrical conductivity of this polymer, i.e. it is said to be photoconductive, has led to important new applications, particularly in xerography. 

Typically, the reaetion would be carried out at 140°C in white spirit with potassium carbazole as a catalyst. Davidge ° has reported problems in polymerisation of V-vinyl carbazole prepared from carbazole obtained from coal tar, attributing this to the presence of sulphur. To overcome these problems carbazole has been prepared synthetically by reactions of cyclohexanone with 

High molecular weight polymers are produced by an adiabatic bulk polymerisation process ° using di-tert-butyl peroxide (0.02%) and 2,2 -azo-bisdi-isobutyronitrile (0.01%) as initiators and pressurised with N2. Heating to 80-90°C causes an onset of polymerisation and a rapid increase in temperature. After the maximum temperature has been reached the mass is allowed to cool under pressure. A typical current commercial material (Luvican M.170) has a A -value of about 70 (as assessed in a 1% tetrahydrofuran solution). 

The polymerisation in situ of monomer impregnated into rolled and stacked condensers was at one time of commercial importance.  

The most important properties of poly(vinyl carbazole) are  

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Most toxicity problems associated with the finished product arise from the nature of the additives and seldom from the polymer. Mention should, however, be made of poly(vinyl carbazole) and the polychloroacrylates which, when monomer is present, can cause unpleasant effects, whilst in the 1970s there arose considerable discussion on possible links between vinyl chloride and a rare form of cancer known as angiosarcoma of the liver. 

Poly(vinyl carbazole) is insoluble in alcohols, esters, ethers, ketones, carbon tetrachloride, aliphatic hydrocarbons and castor oil. It is swollen or dissolved by such agents as aromatic and chlorinated hydrocarbons and tetrahydrofuran. 

The main application today for poly(vinyl carbazole) arises out of its photoconductivity and is in electrostatic dry copying machines. The polymer is applied from solution in thin film (10-15 p.m) layers onto a conductive substrate. 

Scheme 1-20. Poly(vinyl carbazole) and an example of a polymer with an isolated chromo-phore.

Thin film electroluminescent diodes based on poly(vinyl carbazole) Z.-L. Zhang, X.-Y. Jiang, S.-H. Xu, and T. Nagatomo Organic Electroluminescent Materials and Devices, S. Miyata and H.S. Nalwa, Eds., Gordon and Breach, Amsterdam, pp. 203-230... 

The absorption and emission of radiation in the near ultraviolet (UV) and visible regions of the electromagnetic spectrum are associated with electronic (and associated vibronic) transitions involving n- and/or n-electron systems of molecules. Synthetic and natural polymers absorb in the UV region and particularly strong absorption spectra are recorded for polymers containing aromatic and heteroaromatic groups (e.g., poly(styrenes), poly(vinyl naphthalenes), poly(vinyl carbazoles)). 

Luvican Poly(vinyl carbazole) Badische Anilin Soda-Fabrik AG... 

Since semiconductor materials appear to be general candidates for third order effects, it is not surprising that photoconductive charge transfer complexes such as poly(vinyl carbazole)-trinitrofluorenone (PVK-TNF) would exhibit modest DFWM.(142) The observed nonlinearity at 602 nm, a wavelength absorbed by the CT complex, ranges from 0.2 - 2 x 10"11 esu, increasing as the molar fraction of TNF in the complex, PVK TNF, increased. Charge... 

FIG. 17.2 Generalized curve for the thermal conductivity of amorphous polymers. ( ) silicon rubberr (A) polyisobutylene (O) natural rubber (0) polypropylene (A) poly(trifluoro chloro ethylene) ( ) poly (ethylene terephthalate) (V) poly(vinyl chloride) ( ) poly(methyl methacrylate) ( ) poly(bisphenol carbonate) ( ) poly(vinyl carbazole) lines are drawn according to Eq. (17.9). 

The earliest all-organic photoconductive compositions consisted of poly-vinyl(carbazole) (PVK, 1) and 2,4,7-trinitrofluorenone (TNF, 2) [25], In spite of its historical importance, the PVK/TNF system is an unusual one, because it is one of the few photoconductors which acts simultaneously as a photogenerator of primary charges and the medium in which the charge transport is accomplished. It is much more usual to employ a separate charge generator and a distinct transport medium. 

The list of examples of successful Th-FFF separations of lipophilic polymers is extensive and includes polystyrene [29,34,76,118,144,164,165,168,196,200,345-350], polyisoprene [55,110,144,196,349,350], polytetrahydrofuran [144,196,349,350] and poly(methyl methacrylate) [55,110,144,196,349,350], polybutadiene [349], poly(ethyl methacrylate), poly(n-butyl methacrylate), polyfoctadecyl methacrylate), poly(a-methylstyrene), poly(dimethylsiloxane), poly (vinyl acetate), po-ly(vinyl chloride) and poly(vinyl carbazole) [144],polyethylene [351] and other polyolefins [221]. The polyolefin separations were achieved in a special high temperature channel [15,351]. Asphaltenes have also been separated with Th-FFF [352]. 

Composites of polypyrrole and poly(vinyl chloride) have been prepared by several groups (64-67). Polythiophene-poly(vinyl chloride) composites have also been prepared (68). The electropolymerization of pyrrole on poly(vinyl chloride)-coated electrodes yielded composites with mechanical properties (tensile strength, percent elongation at break, percent elongation at yield) similar to poly(vinyl chloride) (65) but with a conductivity of 5-50 S/cm, which is only slightly inferior to polypyrrole (30-60 S/cm) prepared under similar conditions. In addition, the environmental stability was enhanced. Morphological studies (69) showed that the polypyrrole was not uniformly distributed in the film and had polypyrrole-rich layers next to the electrode. Similarly, poly(vinyl alcohol) (70) poly[(vinylidine chloride)-co-(trifluoroethylene)] (69) and brominated poly(vinyl carbazole) (71) have been used as the matrix polymers. The chemical polymerization of pyrrole in a poly(vinyl alcohol) matrix by ferric chloride and potassium ferricyanide also yielded conducting composites with conductivities of 10 S/cm (72-74). 

Judging from the present OLED status, the most important research was Partridge s report on the EL utilized poly(vinyl carbazole) (PVCz) thin films in 1982.26-29 He used the 500-nm-thick PVCz thin films doped with fluorescent molecules as an emissive center, equipped with the efficient hole-injection electrode (SbCls/PVCz) and the electron-injection electrode (cesium) as a low-workfunction metal. Although no quantitative measurement of luminance was described, surprisingly the injection current density reached 1 mA/cm2. Nowadays, we can fabricate very similar OLED devices with superior EL performance. Thus, Partridge s device contributed to establishing the prototypes of present OLED devices. 

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