Cyanoacrylates, substituted

Different aromatic residues have been substituted for the pyrazine and phenyl groups in 9 in order to undertake a systematic investigation of this type of compound. Nakanishi et al. have examined the solid-state photochemistry of l,4-bis[p-pyridyl-(2)-vinyl]benzene (10), p-phenylenediacrylic acid dimethyl ester (11), diethyl ester (12) and diphenyl ester (13), and p-phenylenedi[a-cyanoacrylic... 

Overall polymerization rates which are equated with the rate of propagation were first order in monomer and very fast. At -78 °C the rate constants fell between 1.0 and 3.4 x 1051 mol-1 s 1. Activation energies were very small, 2.2 and 5.5 kJ mol-1 for ethyl (EGA) and butyl (BCA) cyanoacrylates, respectively. Of a range of ammonium, phosphonium, and alkali metal salts only lithium bromide significantly reduced the rate of polymerization. Ogawa and Romero16 found the rate of acrylonitrile polymerization increased by the presence of an ammonium salt but reduced by lithium chloride. There may be a specific interaction between cyano substituted carbanions and the lithium cation. 

Johnston and Pepper35 have found similar behaviour in another anionic polymerization. When dichloromethane was substituted for tetrahydrofuran the rate of amine initiated cyanoacrylate polymerizations fell markedly. The dielectric constants of these two solvents are similar. However, THF is a good donor, weak charge acceptor solvent, methylene chloride the reverse. 

Cyanoacetic acid reacts readily with aliphatic and aromatic carbonyl compounds to form a-cyanoacrylic acids, which can be decarboxylated by heating to give /3-substituted acrylonitriles. ... 

Thermolysis of 6-substituted 3-azidopyridazine 2-oxides gives maleonitrile (236) or cis-j8-cyanoacrylate (237), but the parent compound gives also traces ofa pyrazole (238) (Scheme 12). 

Because a-cyanoacrylates contain a double bond substituted by two electron-withdrawing substituents, they are highly susceptible to anionic initiation, and water is basic enough to initiate very rapid polymerization. Therefore, because moisture can initiate polymerization and because the formed polymer is able to firmly adhere to moist surfaces, it has evoked considerable medical interest as a tissue adhesive (19. 20). 

The Michael addition of enaminones 152 and 154 to ethyl 3-cyanoacrylate gives the substituted pyrrolones 153 and 155, respectively. Scheme 40 (84CPB2821). 

In the context of the anionic polymerization of CA derivatives, as considered in Section 10.3.2.2.1, it is notable that the polymerization of cyanoacrylates is also photoinitiated by substituted pyridine pentacarbonyl complexes of tungsten or chromium, i.e. M(CO)5L with M = Cr or W, and L = 2- or 4-vinylpyridine [60]. Photo-released pyridine adds to CA, and the resulting zwitterion initiates the anionic chain polymerization (see Scheme 10.16). 

Kutal has reported that MLCT excitation of benzoyl-substituted ruthenocenes leads to anionic polymerization of ethyl 2-cyanoacrylate (Equation (31)). These complexes do not undergo ligand loss as a result of MLCT excitation, and it was suggested that the charge redistribution in the excited state allowed the complex to act as an anionic initiator. 

Acrylic adhesives are based on the esters of acrylic and substituted acrylic acids and can be categorized into two main groups the acrylates and methacrylates (I), which cure by free radical-catalysed addition polymerization, and the cyanoacrylates (II), which cure by anion-catalysed addition polymerization. The term acrylic adhesives is normally restricted to include the former, while the latter is usually considered separately (see Cyanoacrylate adhesives) this categorization is adhered to here. 

Recently, D-A-based ter- and quaterthiophenes 2.82 (w = 1, 2) (Chart 1.18) endowed with A-ethylcarbazole and cyanoacrylic acid at each terminus were prepared for their utilization as the active component in dye-sensitized solar cells (DSSCs) [163]. Coupling of the Grignard reagent of 2-bromo-3-hexylthiophene and 3-iodo-9-A-ethylcarbazole yielded carbazole-substituted thiophene. 

Vinyl-substituted cyanoacrylates have been used from time to time, either as modifiers for alkyl cyanoacrylates or on their own as adhesives. These cyanopentadienoates (2) are less reactive toward anionic polymerization than are the cyanoacrylates. This feature allows their preparation from acrolein and a cyanoacetate ester using a Lewis acid catalyst such as zinc chloride. " The monomer can be isolated and purified without going through a depolymerization step. 

Accelerators are substances which increase the rate of polymerization but are not initiators in their own right. Typically, accelerators are compounded in the adhesive, and do not significantly detract from storage stability. The first accelerators described in the patent literature were polyethylene oxides of degree of polymerization (DP) greater than three, and nonionic surfactants having a polyethylene oxide moiety, also with DP greater than three. These ethers are added to the cyanoacrylate in 0.5-10% concentration. The same authors have also patented the use of crown ethers such as 18-crown-6, typically in concentrations of 10 to 1000 ppm, as polymerization accelerators. A variation on the use of crown ethers involves the combination of a substituted furan (0.1-1% concentration) (17,18) with the crown ether (0.05-0.1% concentrations). ... 

The cyanoacrylate olefins have two electron-withdrawing groups on the substituted carbon of the olefin and therefore can be readily polymerized in anionic fashion by use of a base. For example, N,N-dialkyl anilines have been used to activate the polymerization [11]. 

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