3- Vinyl-carbazole monomers

Its main use was as an impregnant for paper capacitors as an alternative to oil impregnation. The capacitors were evacuated and impregnated with vinyl carbazole monomer. A combination of heat and pressure was then used to polymerise the monomer. Polyvinyl carbazole impregnated capacitors gave better sustained high temperature performance than the then conventional oil impregnated capacitors. 

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. 

Applying these methodologies monomers such as isobutylene, vinyl ethers, styrene and styrenic derivatives, oxazolines, N-vinyl carbazole, etc. can be efficiently polymerized leading to well-defined structures. Compared to anionic polymerization cationic polymerization requires less demanding experimental conditions and can be applied at room temperature or higher in many cases, and a wide variety of monomers with pendant functional groups can be used. Despite the recent developments in cationic polymerization the method cannot be used with the same success for the synthesis of well-defined complex copolymeric architectures. 

Typical monomers which polymerise through cationic mechanisms are isobutene, styrene, a-methylstyrene, vinyl ethers and vinyl carbazoles. At present, about 100 vinyl monomers are known that can be polymerised by the cationic initiators. 

The only studies on olefin polymerisations in methylene dichloride in which kp was deduced directly from the rate of reaction were carried out by Ledwith and his collaborators [9, 13] with extremely low concentrations of monomer and catalyst. They polymerised isobutyl vinyl ether and N-vinyl carbazole in a Biddulph-Plesch calorimeter with trityl or tropylium salts and obtained the first-order rate constants k1 from the conversion curves. Since different catalysts gave the same ratio of kx c they concluded that for each of them Xxr = c0 and hence identified with kp which must in fact be k p, as explained above. It seems unlikely that if several initiators give the same value of kp, they do so because they are all equally inefficient, and the inference that they do so because they are all 100% efficient, i.e., that for all of them x = c0, seems plausible - but it would be useful to have a direct check of this. 

The calorimetric method was applied by Bowyer et al. (1971) to the polymerisation of N-vinyl carbazole (NVC) by tropylium hexafluoroantimonate and perchlorate in CH2C12 at 0 °C and -25 °C. The reactions were very fast and the reaction curves had a monotonically decreasing rate from the start. The initial reaction rate, R0, was correlated with the initiator and monomer concentrations by the equation... 

The simplest procedure for grafting copolymerization, in terms of number of components in the reaction medium, is a bulk polymerization of the monomer in mixture with the molten polyamide. This has been claimed in an earlier patent (2), related to improvements in dyeability and hydrophylic properties of the resulting yam, obtained by melt spinning of the product of reaction with monomers such as 2,5-dichloro styrene, lauryl methacrylate, N-vinyl pyrrolidone, and N-vinyl carbazole. 

Cyclic monomers such as cyclohexene oxide were readily polymerized upon irradiation of the CT complexes of pyridinium salts whereas spontaneous polymerizations were observed upon mixing with strong electron donating monomers such as butyl vinylether and A-vinyl carbazole. These monomers are known to form CT complexes themselves with electron acceptors which may interfere with the rapid polymerization observed. 

Many specific examples of reaction type (81) have been described, and iheir number has been increasing. In many of these, vinyl carbazole is the donor. Other monomers can also react in a similar way [304]. 

There exist many alternating copolymerizations ethylene or propene with alkyl acrylates [244], vinyl acetate with maleic anhydride [245], styrene with acrylonitrile [246], styrene with fumaronitrile [247], vinyl carbazol with fumaronitrile, vinyl ferrocenne with diethylfumarate [248], and further pairs or systems of three monomers [238, 249-253]. External conditions can support or hinder alternation. At not too high temperatures, vinyl acetate forms a donor—acceptor complex with maleic anhydride. Under these conditions (and in the presence of a radical initiator), an alternating copolymer is formed. The concentration of the complex decreases with increasing temperature above 363 K the complex cannot exist. Under these conditions, copolymerization yields a statistical copolymer whose composition depends on the composition of the monomer mixture [245]. 

When the monomer is attached to the active centre in a manner leading to the formation of a weakly reactive ion, growth is terminated. A typical example of this kind of termination is the formation of an unreactive ion during cationic polymerization of vinyl carbazole. Instead of propagation... 

Other Lewis Acids. Several relatively weak Lewis acids such as zinc halides and mercury halides initiate polymerization of the most reactive monomers such as N-vinyl carbazole, vinyl ethers, and alkoxysty-renes. Many of these acids have poor solubility in hydrocarbons and halo-genated hydrocarbons and are therefore used as acetone or ether solutions. However, such solvents act as nucleophiles, and therefore decrease the acids Lewis acidity. 

Other monomers that are suitable for cationic polymerization include cyclic ethers (like tetrahydrofuran), cyclic acetals (like irioxane), vinyl ethers, and N-vinyl carbazole. In these cases the hetero atom is bonded directly to the electron deficient carbon atom, and the respective carboxonium ion (9-13) and immonium ion (9-14) arc more stable than the corresponding carbocalions. 

The behaviour of poly(N-vinyl carbazole) is certainly complex, and an attanpt has been made recently to gain an insight into the photophysical properties of this polymer by studying the related compounds below. Monomer fluorescence is observed in these compounds... 

Anionic polymerizations of A-ethyl-2-vinyl-carbazole and A-ethyl-3-vinyl-carbazole have also been examined, and the 2-vinyl derivative shown to yield clean living systems. However, the 3-vinyl monomer is very much more reactive and polymerization must be conducted below — 60 °C to get any approximation to a living system. No quantitative information is available. 

Triphenylmethyl halides and tropylium halides ionize to form trityl, (f>3C, and cycloheptatrienyl (tropylium), CyRt", carbocations [Eqs. (P8.20.1) and (P8.20.2)], which are too stable to efficiently polymerize less reactive monomers such as isobutylene and styrene, but polymerization of p-methoxystyrene, vinyl ethers and N-vinyl carbazole, which are more reactive, proceeds rapidly. 

The only studies on olefin polymerisations in methylene dichloride in which kp was deduced directly from the rate of reaction were carried out by Ledwith and his collaborators (9, 13) with extremely low concentrations of monomer and catalyst. They polymerised isobutyl vinyl ether and N-vinyl carbazole in a Biddulph-Plesch calorimeter with trityl or tropylium salts and obtained the first-order rate constants kt from the conversion curves. Since different catalysts gave the same... 

The monomers, N-vinyl carbazole (NVC), methacrylamide (MAM), octadecyl methacrylate (ODMA) and trichloroethyl methacrylate (TCEM) were obtained from Polyscience, Inc. Diphenyl acetylene (DPAE), poly(4-chlorostyrene) (PC1S), poly(butadiene) (PBD), poly(styrene) (PS) were obtained from Aldrich Chemical Co. Poly (vinyl alcohol) (PVA), 99-100% hydrolyzed, was obtained from J. T. Baker Chemical Co. Poly(vinyl pyrrolidone) was obtained from Sigma Chemical Co. 

Hydrophobic fluorescent probes have been bound onto copolymers of 2-dialkylaminoethyl methacrylate-N-vinyl-2-pyrrolidone and compared with effects of dye binding l and in an amphiphilic copolymer of jl-styrenesulphonate with butyl methacrylate containing vinyl carbazole as a fluorescent probe only monomer fluorescence was observed especially in water where the polymer formed latex particles . two molecular populations have been observed for an oxadiazole dye in poly(l-trimethylsilyl-l-propyne)353 while a... 

Reinvestigation of Pleseh s work confirmed their kinetic conclusions, viz. the first order kinetics in monomer, and led to a similar rate constant. However, addition of oxetane to the vinyl-carbazole-tetranitromethane system greatly retarded the vinyl-car-bazole polymerization, e.g. by a factor of 30, but neither the first order character of this reaction nor the molecular weight of the resulting polymer was affected provided that the concentration of oxetane was sufficiently large. At the same time, cationic polymerization of the added oxetane was observed. 

No true living cationic vinyl polymers are known at present, although the papers of Skorokhodov on 1,2-dimethoxyethylene 1011 and of Higashimura on the I2-initiated polymerization of vinyl ethers, p-methoxystyrene (Sect. 15.3.1.1.3) and of N-vinyl carbazole 102) approach living features. It is possible, however, to prepare a vinyl polymer with an end-group that is inactive towards its own monomer but is able to convert a heterocyclic monomer into the onium ion, in this way starting the polymerization of a second monomer. The application of this approach for the synthesis of block copolymers is described below. 

The polymerization of A -vinyl carbazole may be initiated by free radicals, by cations, by organometallic catalysts, by charge-transfer processes, or by electrochemical methods. Since the monomer is a solid at room temperature (m.p. 64-66°C, b.p. 154-155°C/3 mm), solid state polymerizations have been carried out both on powdered monomer and on the surfaces of larger crystals. In this process, the reactive species propagates into the interior of the solid. 

In a heterogeneous system, powdered biosynthesized y-poly(glutamic acid), in the free acid form, has been used to initiate the polymerization of IV-vinyl-carbazole as well as AT-vinyl-2-pyrrolidone. The rate of polymerization in nitrobenzene was greater than in toluene. In the process, there was no significant grafting onto the surface of the y-poly(glutamic acid). It has been proposed that initiation involves proton addition from the surface of the carboxylic acid to the monomer. The propagation proceeds with carboxylate anions on the surface of a counter ion [60]. 

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