Pyridinium Modified Polymers

Biodegradable polymers can be obtained by introducing pyridinium groups such as N-alkylpyridinium groups or N-arylpyridin-ium groups into the backbone of a synthetic vinyl polymer and subsequently quatemizing the pyridinium groups with chlorine or 

The polymerization is guided as a radical polymerization using dibenzoylperoxide, 2,2 -azobisisobutyronitrile or ammonium persulfate as initiator. The backbone can be modified by the reaction of 4-vinylpyTidine with benzyl chloride to get N-benzyl-4-vinylpyrid-ine monomers (41). 

The biodegradable polymers have high compatibility with microbial cells so that articles molded or otherwise formed from the biodegradable pol5mers can be easily decomposed by activated sludge or under conditions buried in the ground (41). 

---

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. 

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). 

The organic-inorganic hybrid materials have shown significant increases in properties compared to the conventional composites or neat polymers. The degree of dispersion of nanofiUers in a polymer matrix and the processing method play a key role on the final properties of the materials. Key objectives of researches are to design nanocomposites with enhanced properties at low filler contents. Different modified clays have been used in view of these objectives [31,52], There are reports on the use of ammonium-treated layered silicates [52,53], whereas the use of thermostable ILs such as pyridinium, imidazolium, or phosphonium is poorly reported. However, their combinations with poly(styrene) (PS) [54], PE [55], PP [56], poly(vinylidene fluoride) (PVDF) [57], and PET matrices [58] have been reported in the literature. 

ILs based on pyridinium, imidazolium, or phosphonium cations to modify layered silicates (fillers) according to the nature of the polymer matrices have been reported. Recently, these types of ILs are emerging as new alternatives for the design of thermally stable organically modified clays. 

For the coupUng reaction, it is useful to exchange the protons of the sulfonic acids for organic cations, such as pyridinium or trimethyl benzylam-monium. hi order to modify the polymer properties, some of the sulfonic acid groups can be used to introduce aromatic substituents by sulfone formation. 

Stoeffler et al. [70] also tried imidazolitun and phosphonium salts together to pyridinium salts as surfactants for Mt to obtain PE nanocomposites. Most of authors modified the Mt with the amount of salt required to intercalate 100% of the CEC of the Mt. Mandalia and Bergaya [71] studied the effect of surfactant/CEC ratio, obtaining that the amount of surfactant had a direct effect on the interlayer separation of the clay, and with clay mineral having a high surfactant load (150 to 200% of CEC) the polymer intercalation was more homogeneous. 

Montmorillonites modified with alkyl pyridinium, imidazolium and phosphonium intercalants were successfully synthesized. Compared to commercial Cloisite 20A, enhancements in thermal stability of +31°C to +70°C were observed in inert atmosphere. The products evolved upon thermal decomposition of the various organoclays were analyzed by mass spectroscopy. Preliminary results indicate that the major part of the volatile by-products is constituted by alkenes and alkanes. Chloromethane was detected between 200°C and 280°C in unpurified Cloisite 20A. CiePy-MMT was found to liberate pyridine above 220°C. Such informations can be of considerable interest regarding the processing conditions of polymer nanocomposites and their subsequent applications. 

---