N-Vinylcarbazoles

A substantial number of photo-induced charge transfer polymerizations have been known to proceed through N-vinylcarbazole (VCZ) as an electron-donor monomer, but much less attention was paid to the polymerization of acrylic monomer as an electron receptor in the presence of amine as donor. The photo-induced charge-transfer polymerization of electron-attracting monomers, such as methyl acrylate(MA) and acrylonitrile (AN), have been recently studied [4]. In this paper, some results of our research on the reaction mechanism of vinyl polymerization with amine in redox and photo-induced charge transfer initiation systems are reviewed. 

Homopolymerization of the olefin occurred if its basicity was higher than that of 2-furaldehyde, i.e. the initiator displacement from the complex was strong and thereafter only occasional inclusion of aldehyde in the growing polymer chain took place 2-furaldehyde units in the products were less than 5%. This situation was observed with acenaphthylene and N-vinylcarbazole. 

It is to be noted that N-vinylcarbazole (NVC) undergoes also living cationic polymerization with hydrogen iodide at —40 °C in toluene or at —78 °C in methylene chloride and that in this case no assistance of iodine as an activator is necessary 10d). NVC forms a more stable carbocation than vinyl ethers, and the living propagation proceeds by insertion between the strongly interacting NVC-cation and the nucleophilic iodide anion. 

In the case of undoped PVCa films, impurities and surface states dominate the photoconduction mechanism (6) leading one to question any study of intrinsic pKotoconduction in organic polymers. Poly(N-vinylcarbazole) films yellow under ambient laboratory conditions. Work in our laboratory (7) has shown that ageing of a purified sample of PVCa leads to an increase in photoresponse in the 350-450 nm region while there is an initial drop in photoresponse in the 250-... 

Fig. 9 (a) Molecular structures of novel ESIPT dyes, 2,5,-bis[5-(4-t-butylphenyl)-[l,3,4]oxadia-zol-2-yl]-phenol (SOX), and 2,5-bis[5-(4-t-butylphenyl)-[l,3,4]oxadiazol-2-yl]-benzene-l,4,-diol (DOX). (b) Emission colors in the Commission Internationale de L Eclariage (CEE) chromaticity diagram. The inner oval and the filled circle at coordinate (x,y) of (0.33, 0.33) indicate the white region and the ideal color, respectively. Note that PS and PVK denote polystyrene and poly (N-vinylcarbazole) film (reprint from ref. [91], Copyright 2005 Wiley-VCH)... 

WD Gill, Drift mobilities in amorphous charge-transfer complexes of trinitrofluorenone and poly-n-vinylcarbazole, J. Appl. Phys., 43 5033-5040, 1972. 

By fluorescence analyses just upon laser ablation and of ablated surface, Molecular aspects of ablation echanisa were elucidated and a characterization of ablated Materials was perforaed. Laser fluence dependence of poly(N-vinylcarbazole) fluorescence indicates the iaportance of Mutual interactions between excited singlet states. As the fluence was increased, a plasna-like eaission was also observed, and then fluorescence due to diatonic radicals was superinposed. While the polyner fluorescence disappeared Mostly during the pulse width, the radicals attained the naxinun intensity at 100 ns after irradiation. Fluorescence spectra and their rise as well as decay curves of ablated surface and its nearby area were affected to a great extent by ablation. This phenonenon was clarified by probing fluorescence under a Microscope. 

In the present work, we have examined poly(N-vinylcarbazole) (abbreviated hereafter as PVCz) and pyrene-doped poly(aethyl methacrylate) (PMMA) films by using a tine-resolved fluorescence spectroscopic aethod. Fluorescence spectra and their dynanic behavior of the forner fila were elucidated with a high intensity laser pulse and a streak camera, which nakes it possible to neasure dynaaics just upon laser ablation. This aethod reveals aolecular and electronic aspects of laser ablation phenomena (17). For the latter fila a laser pulse with weak intensity was used for characterizing the ablated and Basked areas. On the basis of these results, we demonstrate a high potential of fluorescence spectroscopy in aolecular studies on laser ablation and consider its mechanism. Experimental... 

J. Pac, P. H. Plesch, The Polymerisation of N-Vinylcarbazole by Electron Acceptors, Part I, Kinetics, Equilibria, and Structure of Oligomers Part II, Discussion, Polymer, 1967, 237. 

A detailed study of the polymerization of N-vinylcarbazole by tetranitromethane has provided strong evidence that in this system the reaction is propagated by a very small concentration of carbonium ions [25]. 

This idea was put forward first by Scott, Miller and Labes [57] for the polymerization of N-vinylcarbazole by organic electron-acceptors. It was then applied to initiation by the tropylium and other ions [52,58] by reducible metal ions but with emphasis on a possible radical reaction [59] and by sodium chloroaurate in which Au(III) is reduced (see also Section 4.5) [60]. Then Plesch suggested [6] an application of the idea of catalysis by metal halides generally, giving as an example, the following hypothetical scheme ... 

Another mode of termination by monomer, which has been suggested for the polymerization of N-vinylcarbazole, is formation of a quaternary ammonium ion from the growing cation and the monomer [25] which is essentially the same as reaction (XIa). 

The formation of w-donor complexes (IV). This involves stronger forces than the previous two types because the lone pair of the hetero-atom is involved. It is clear that the polymerisations of some of the favourite monomers, such as the alkyl vinyl ethers, 4-MeO-styrene, and N-vinylcarbazole may be dominated by this phenomenon. A corollary of the complexation by an w-donor monomer is that the hetero-atoms in the corresponding polymers will also interact with the growing carbenium ions. The authors who have proposed this include Stannett (alkyl vinyl ethers) [11], Boelke (dimethoxyethene) [12], and Sauvet (4-MeO-St) [7]. 

Unless the monomer contains a hetero-atom, the polymer is likely to be much less polar and polarisable than the monomer and the solvent and therefore negligible as an ion solvator but for monomers such as p-MeO-styrene, the alkyl vinyl ethers, or N-vinylcarbazole, the polarity of their polymers is such that they can make a significant contribution to the solvation of Pn+, especially if the solvent is of low polarity. Therefore the species Pn+Pm and, presumably, Pn+PmA must be considered as parts of the ionic population in certain systems. 

The second model involves the reversible formation of a complex between the iodine and the monomer, and in this context it is unimportant whether the iodine forms an n-complex, e.g., with the O-atom of a vinyl ether, or a 7t-complex with a double-bond or an aromatic ring of the monomer (styrene, N-vinylcarbazole) the only important point is that the complexed monomer is very much more reactive with the propagating ester group than the uncomplexed monomer, and that its formation is an equilibrium reaction. [Very detailed studies of the reactions of iodine with styrene [38] and with butyl vinyl ether (nBVE) [39, 40] have been reported in which the formation of various complexes is discussed.]... 

Spectroscopic Studies on Carbonium Ions derived from Aromatic Olefins. Part II. Acenaphthylene, N-Vinylcarbazole, and Tetraphenylethylene, A. Gandini and P.H. Plesch, Journal of the Chemical Society, (B), 1966, 7-10. 

Impurity Effects in the Polymerisation of N-vinylcarbazole by Mercuric Chloride, M.A. Hamid, M. Nowakowska and P.H. Plesch, Die Makromolekulare Chemie, 1970, 132, 1-5. 

Thermally stimulated hole current in poly-N-vinylcarbazole shows distinct maximum at around 5°C and another large current above 100°C. This 5°C maximum is due to 0.56 eV hole traps of 7 x 1015 cm 3 density. Photoconductivity in poly-N-vinylcarbazole increases appreciably when irradiated with UV-light in air at room temperature and this increase accompanies the formation of 0.56 eV hole traps. The nature of this traps has been discussed. 

Poly-N-vinylcarbazole is one of the very important organic photoconductors now in use in electrophotography. For practical use, a little amount of sensitizer is usually added. 

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