PYRIDINIUM POLYMER

Quaternary pyridinium polymers can show biological activity when bound to surfaces, e.g., poly(4-vinyl pyridine)-modified glass surfaces which were modified using different alkyl bromide derivatives. Suitable polymers for antibacterial applications not only exhibit antibacterial activity, but also non-toxicity to human cells (i.e., selectivity). 

Pyridinium polymers have also been used as the basis of antimicrobial surfaces. " The more effective polymers... 

Similar to the biguanide structures, Dizman et al. created l,4-diazabicyclo[2.2.2]octane (DABCO)-based stmctures carrying two quaternary ammonium charges with butyl and hexyl alkyl extensions (C12). The monomer was assembled by multiple nucleophilic substitution reactions. Polymers were formed by free radical polymerization in water. These polymers, much like the biguanide acrylate and pyridinium polymers, combined hydrophobidty and cationic charge on the same monomer. One difference is that the cationic charge was also separated from the backbone of the polymer by a long alkyl chain. As with the pyridine polymers, the hexyl alkyl monomers were found to be the most effective biocides. 

Polymers in Schemes 12 and 13 were the first examples of the preparation of pyridinium and iminopyridinium ylide polymers. One of the more recent contributions of Kondo and his colleagues [16] deals with the sensitization effect of l-ethoxycarbonyliminopyridinium ylide (IPYY) (Scheme 14) on the photopolymerization of vinyl monomers. Only acrylic monomers such as MMA and methyl acrylate (MA) were photoinitiated by IPYY, while vinylacetate (VA), acrylonitrile (AN), and styrene were unaffected by the initiator used. A free radical mechanism was confirmed by a kinetic study. The complex of IPYY and MMA was defined as an exciplex that served as a precursor of the initiating radical. This ylide is unique in being stabilized by the participation of a... 

We recently synthesized cationic polymers containing imidazole (e g. 68 (SZ811) and 69 (SZ11—3—3)] by reacting poly [N-(2,4-dinitrophenyl)-4-vinyl-pyridinium chloride] with histamine or histamine mixed with other amino derivatives ll8 The hydrolyses of neutral and anionic esters with the models followed saturation kinetics in alkaline media. 

If the film is nonconductive, the ion must diffuse to the electrode surface before it can be oxidized or reduced, or electrons must diffuse (hop) through the film by self-exchange, as in regular ionomer-modified electrodes.9 Cyclic voltammograms have the characteristic shape for diffusion control, and peak currents are proportional to the square root of the scan speed, as seen for species in solution. This is illustrated in Fig. 21 (A) for [Fe(CN)6]3 /4 in polypyrrole with a pyridinium substituent at the 1-position.243 This N-substituted polypyrrole does not become conductive until potentials significantly above the formal potential of the [Fe(CN)6]3"/4 couple. In contrast, a similar polymer with a pyridinium substituent at the 3-position is conductive at this potential. The polymer can therefore mediate electron transport to and from the immobilized ions, and their voltammetry becomes characteristic of thin-layer electrochemistry [Fig. 21(B)], with sharp symmetrical peaks that increase linearly with increasing scan speed. 

The utilization of solid-support pyridinium salts in the synthesis of bicyclic pyridines has been reported. Yue et al. synthesized 1,2,3,7-tetrasubstituted indolizines using poly(ethyleneglycol)bound pyridinium salts <06JHC781>. The PEG-bound pyridinium salts 53 were reacted with alkenes or alkynes in the presence of Et3N, via 1,3-dipolar cycloaddition, to give polymer-bound indolizines 54 and 55, respectively. Liberation of the heterocycle with KCN/MeOH afforded 1,2,3,7-tetrasubstituted indolizines 56 and 57 in good to excellent yield. 

Photocrosslinking. The second class of photopolymer chemistry that is used in some commercial products is based on the reaction of unsaturated moieties attached to an organic polymer. These photopolymer materials include the [2+2] cycloaddition of the ethylenic groups in poly(vinyl cinnamate) polymers and in the newer styryl pyridinium (10) and thiazolium (77) derivatives of poly(vinyl alcohol). The main advantage of this chemistry is that, unlike free-radical photopolymerization, they are insensitive to the presence of oxygen. This photopolymer mechanism is principally used in applications employing a washout development process (e.g. resists). 

The utilization of polar polymers and novel N-alkyl-4-(N, N -dialklamino)pyridinium sedts as stable phase transfer catalysts for nucleophilic aromatic substitution are reported. Polar polymers such as poly (ethylene glycol) or polyvinylpyrrolidone are thermally stable, but provide only slow rates. The dialkylaminopyridininium salts are very active catalysts, and are up to 100 times more stable than tetrabutylammonium bromide, allowing recovery and reuse of catalyst. The utilization of b is-dialkylaminopypridinium salts for phase-transfer catalyzed nucleophilic substitution by bisphenoxides leads to enhanced rates, and the requirement of less catalyst. Experimental details are provided. 

Spurred by our desire to avoid use of expensive dipolau aprotic solvents in nucleophilic aromatic substitution reactions, we have developed two alternative phase transfer systems, which operate in non-polar solvents such as toluene, chlorobenzene, or dichlorobenzene. Poleu polymers such as PEG are Inexpensive and stable, albeit somewhat inefficient PTC agents for these reactions. N-Alkyl-N, N -Dialkylaminopyridinium salts have been identified as very efficient PTC agents, which are about 100 times more stable to nucleophiles than Bu NBr. The bis-pyridinium salts of this family of catalysts are extremely effective for phase transfer of dianions such as bis-phenolates. 

The oxamate group has been incorporated into a vinyl polymer by Kirsh and Kabanov 41). These workers prepared a copolymer of 4-vinyl-A -(phenacyloxime)pyridinium bromide and vinylpyridine. For the hydrolysis of p-nitrophenyl acetate the oxamate polymer produced a significant rate enhancement over the monomeric analogs. 

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