Cationic monomer

If the nucleophilicity of the anion is decreased, then an increase of its stability proceeds the excessive olefine can compete with the anion as a donor for the carbenium ion, and therefore the formation of chain molecules can be induced. The increase of stability named above is made possible by specific interactions with the solvent as well as complex formations with a suitable acceptor 112). Especially suitable acceptors are Lewis acids. These acids have a double function during cationic polymerizations in an environment which is not entirely water-free. They react with the remaining water to build a complex acid, which due to its increased acidity can form the important first monomer cation by protonation of the monomer. The Lewis acids stabilize the strong nucleophilic anion OH by forming the complex anion (MtXn(OH))- so that the chain propagation dominates rather than the chain termination. 

Care must be taken not to mistake bands arising from 1 1 or 1 2 van der Waals complexes (e.g. toluene-Arx, x = 1 and 2) for monomer bands. Fragmentation of either the neutral excited state or the cation can cause the 1 1 and even the 1 2 bands to appear in R2PI spectra detected at the monomer cation mass. The van der Waals bands usually appear red-shifted by a constant value from corresponding strong monomer bands. The safest way to identify van der Waals bands is to carry out R2PI scans gated on successive toluene-Ar masses to see which bands disappear at each step. 

However, despite all these observations, it is still unclear which additional coupling steps take place after the nucleation of an oligomeric layer on the electrode. In the literature, experimental data have been presented to support the view that, with the formation of an oxidized prefilm , the process gradually transforms into one in which the chain growth can take place on the surface immediately by coupling of the monomer cation radical and the oxidized chain in the film [67]. However, the assumption of heterogeneous coupling of monomers... 

Generally, at least in theory, an important aspect of cation-radical polymerization, from a commercial viewpoint, is that either catalysts or monomer cation-radicals can be generated electrochem-ically. Such an approach deserves a special treatment. The scope of cation-radical polymerization appears to be very substantial. A variety of cation-radical pericyclic reaction types can potentially be applied, including cyclobutanation, Diels-Alder addition, and cyclopropanation. The monomers that are most effectively employed in the cation-radical context are diverse and distinct from those that are used in standard polymerization methods (i.e., vinyl monomers). Consequently, the obtained polymers are structurally distinct from those available by conventional methods although the molecular masses observed so far are still modest. Further development in this area would be promising. 

Shibasiki Y, Sanada H, Yokoi M, Sanda F, Endo T (2000) Activated monomer cationic polymerization of lactones and the application to well-defined block copolymer synthesis with seven-membered cyclic carbonate. Macromolecules 33 4316-4320... 

The polymerization of lactams (cyclic amides) can be initiated by bases, acids, and water [Reimschuessel, 1977 Sebenda, 1976, 1978 Sekiguchi, 1984]. Initiation by water, referred to as hydrolytic polymerization, is the most often used method for industrial polymerization of lactams. Anionic initiation is also practiced, especially polymerization in molds to directly produce objects from monomer. Cationic initiation is not useful because the conversions and polymer molecular weights are considerably lower. 

A species believed to be the monomer cation radical of 9-ethylcarbazole as a green solution in acetonitrile formed by oxidation of 9-ethylcarbazole with iodine-silver(I) perchlorate, was detected by ESR spectroscopy, although the perchlorate of the cation radical could not be isolated subsequent treatment with potassium iodide gave 9,9 -diethyl-3,3 -bicarbazole. The borofluoride salts generated as crystalline materials by oxidation of carbazole or 9-methylcarbazole with tropylium borofluoride in acetonitrile followed by precipitation with methanol are not salts of the monomer cation-radicaP as originally believed. Russian workers have suggested that nitration of carbazole proceeds via a cation radical. ... 

Individual rate constants for homogeneous and heterophase DADMAC homopolymerizations have been calculated from the kinetic models above. These constants are summarized in Table 4. The overall activation energies, also given in Table 4, are relatively high. These values likely result from the electrostatic repulsion between the positively charged radicals and the monomer cations. 

Fig. 7- Intermediate and product species formed in the dimerization and the polymerization of vinylcarbazole in nitrobenzene (N02) and be-nzonitrile (C/V) in the presence of oxygen (VCZ ) monomer cation radical (> cyclodimer (P) polymer [43]...

In the aerated solution of /V-vinylcarbazole in benzonitril, the observed spectrum was similar to that of the dimer cation, whereas the spectrum observed in nitrobenzene was comprised of monomer cation and polymer cation [43]. This implies the formations of cyclodimer and polymer through the dimer cation and the polymer cation, respectively. From the measurements with the mixed solvents of benzonitril and nitrobenzene, the relative amounts of intermediate species and final products were obtained as functions of solvent composition. The results are illustrated by Fig. 7 [43]. 

Such polycyclic aromatic hydrocarbons as anthracene or heteroaromatics as acridine, phenazine and 2,4,5-triphenyl oxazole act as Jt-donors for the Jt-acceptors AN and alkyl methacrylates [50-53]. Again, the interaction of the donor excited states with vinyl monomers leads to exciplex formation. But, the rate constants (k ) of these quenching processess are low compared to other quenching reactions (see Table 1). The assumed electron transfer character is supported by the influence of the donor reduction potential on the k value (see Table 1), and the detection of the monomer cation radicals with the anthracene-MMA system. Then, the ion radicals initiate the polymerization, the detailed mechanism of which is unsolved,... 

One proposed mechanism for the electrochemical polymerization of aniline is shown in Fig. 66 [287]. Aniline is oxidized to cation radical 445 which dimerizes to form dication dimer 446. Deprotonation (- 2H +) of 446 gives 443. The oxidation of dimer 443 gives cation radical 447 which is further oxidized to diiminium dication 448. The coupling of 448 with 445 followed by the loss of two protons gives 449. The addition of aniline units to the polymer chain continues in a similar manner by the coupling of the terminal diiminium dication group with monomer cation radical 445. 

Proton transfer to monomer is the best known and most widely studied transfer reaction in the cationic polymerization of vinyl monomers. Cationic polymerization of styrene and isobutylene belong to the comprehensively studied examples More recently, it has been shown by H-NMR that there are two kinds of double bonds formed as result of transfer in the polymerization of isobutylene ... 

This type of lactam polymerization is initiated under anhydrous conditions with acids or acid salts which do not split off water at the polymerization temperature (e.g., lactam or amine hydrochloride) as well as with some Lewis acids [176, 177]. The activated species is the monomer cation which takes part both in the initiation and propagation reactions. 

The results show that DMF inhibits the copolymerization completely. However, CHC13 and CHjCL accelerate the copolymerization. It is known that halogenated hydrocarbons (RX) capture elctrons via dissociative electron attachment and stabilize monomer cation M +. 

The lifetime of monomer cation should be lengthened, and a cationic polymerization is then favored to proceed under such circumstances. 

M. Sangermano, M.A. Tasdelen, and Y. Yagci, Photoinitiated curing of mono- and hifunctional Epoxides hy combination of active chain end and activated monomer cationic polymerization methods. J. Polym. Sci. A Polym. Chem. 2007, 45(21), 4914-4920. 

The initiator cation formed in this way can, in many cases then add directly on to the monomer to form the monomer cation. Examples of this are the polymerization of p-methoxystyrene or epoxides with trityl hexa-chloroantimonate, the polymerization of tetrahydrofuran with acetyl perchlorate, and the polymerization of vinyl ethers and A -vinyl carbazole with tropylium hexachloroantimonate, for example ... 

The classical conception of Br0nsted acids such as HCIO4 is that they dissociate into protons and gegenions. The proton adds onto a monomer, and the monomer cation produced then starts the polymerization of further monomer, i.e.,... 

The new monomer cation then starts another polymer chain. If, on the other hand, isobutylene (or even norbornadiene) is polymerized with AICI3, saturated end groups and an unsaturated monomer cation are primarily formed. This cation then starts the polymerization of another polymer chain, whereby the unsaturated group formed in this way is aluminated by the initiator. Thus, each polymer molecule contains an aluminum atom, produced as in equation (18-98) or equation (18-101) ... 

N. G. Gaylord, One-electron transfer initiated polymerization reactions, I. Initiator through monomer cation radicals, Macromol. Revs. 4, 183 (1970) [/. Polym. Sci. D4, 183 (1970)]. 

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