Thermal Behavior, Stability, and Decomposition Mechanism of Poly(N-vinylimidazole)

Abstract

Homo- and copolymers of N-vinylimidazole belong to a rapidly emerging class of polymeric materials. Because of the fact that these materials can be utilized in several high-temperature processes and applications, such as catalysis, fuel cells, polymeric ionic liquids (PIL), precursors for new materials by thermolysis, etc., and because fundamental details on the thermal behavior of such polymers are lacking, systematic investigations have been carried out to reveal the stability and the mechanism of thermal decomposition of poly(N-vinylimidazole) (PVIm) by using a variety of techniques, such as differential scanning calorimetry (DSC), thermogravimetry (TG), thermogravimetry–mass spectrometry (TG-MS), and pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS). The investigated PVIm was obtained by free radical polymerization initiated by AIBN in benzene at 70 °C. By the unique combination of the applied methods to investigate the thermal decomposition mechanism of PVIm, it was found that the thermal decomposition of PVIm takes place in one main step in the temperature range 340–500 °C. An initial mass loss of 4% occurs before the main endothermic decomposition step due to the evaporation of water and acetone physically bound to the polymer during purification. The major products of the thermal decomposition of PVIm are 1H-imidazole and 1-vinylimidazole accompanied by several minor products, such as benzene and several alkyl aromatics. The relative ratios between imidazoles and aromatics, i.e., the 2 orders of higher amounts of imidazoles, indicate that in contrast to other polymers with heteroatom pendant groups, e.g., poly(vinyl chloride) (PVC), poly(vinyl acetate), (PVAc) and poly(vinyl alcohol) (PVA), not zip-elimination of 1H-imidazole but homolytic scission of the carbon–nitrogen bond is the main reaction of its formation. 1-Vinylimidazole is formed by main chain scission followed by depolymerization. Both 1H-imidazole and 1-vinylimidazole formation lead in part to macroradicals and short conjugated double bond sequences (polyenes) in the chain, the thermolytic cyclization, isomerization, and aromatization of which result in the low amounts of aromatics. These findings served for the basis of formulating the mechanism of the thermal decomposition of PVIm, which can be utilized in the course of further investigations with this unique polymer.

Thermal stability and decomposition mechanism of 1-ethyl-3-methylimidazolium halides

“…). The dominance of homolytic cleavage of C-N-bonds of the imidazolium ring is also described for decomposition of poly (N-vinylimidazole) [29]. Cl + ) (Fig.…”

Unexpected thermal decomposition behavior of poly(N-vinylimidazole)-l-poly(tetrahydrofuran) amphiphilic conetworks, a class of chemically forced blends

“…Table 1 The feed ratios, compositions, M c values, decomposition temperatures and char yields of poly(N-vinylimidazole)-l-poly-(tetrahydrofuran) (PVIm-l-PTHF) conetworks, the poly(tetrahydrofuran) dimethacrylate (PTHFDMA) macromolecular cross-linkers and the poly(N-vinylimidazole) (PVIm) homopolymer a Sample VIm/PTHF feed ratio (wt%) PVIm/PTHF in the conetwork (wt%) the methacrylate-telechelic and hydroxyl-telechelic PTHF samples are essentially identical. 11 Removing the residual solvents by heating at 50 C (to avoid any kind of preliminary degradation) under vacuum was not sufficient to completely eliminate the solvents which are responsible for the early weight losses below the decomposition temperatures. The T d(max) for the PTHFDMA macromononomers is observed between 400 and 407 C ( Fig.…”

“…5i shows the decomposition of PVIm takes place in the temperature range of 360-480 C, that is at signicantly higher temperature than that of PTHF, and 5% solid residue remains due to char formation reactions taking place in the temperature range of 500-700 C. (See Fig. 11 The TG-MS ion proles at m/z 68 and m/z 94 indicate the two most typical products of PVIm, namely 1H-imidazole and 1-vinylimidazole, respectively. It should be noted that the mass loss up to 200 C is due to adsorbed water, moreover further negligible mass loss can be detected until 340 C which is caused by the liberation of included acetone.…”

“…10 In a previous study by us 11 the characterization of the thermal properties, behavior and unique degradation mechanism of poly(N-vinylimidazole) (PVIm) homopolymer were reported on the basis of the combination of different thermal analysis methods. The application elds of imidazole-containing synthetic polymers and its derivatives are of great current interest, such as being a component in fuel cells, 1 ion imprinted and metal ion complexing matrices, 2 catalyst and catalyst supports, 3 corrosive protective coatings, 4 electrophoresis medium, 5 additive in wine production, 6 enzyme immobilization carrier, 7 gene delivery vectors, 8 biomaterials with various pharmacological activities 9 and articial enzymes.…”

Free radical polymerization of caffeine‐containing methacrylate monomers

“…[42][43][44] CMA, however, does not contain any beta hydrogens eliminating the common route as a possible mechanism for caffeine loss. Fodor et al 45 extensively researched the thermal decomposition of poly(N-vinylimidazole) using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). This highly sensitive analytical technique identified 10 different small molecule byproducts, one of them Figure 8 depicts the proposed mechanism (left) constructed to support imidazole as a decomposition product.…”