Polychloroprene, thermal degradation

The influence of additives on thermal degradation may be exemplified by the FTIR-EGA study of the effect of zinc oxide on the pyrolysis of polychloroprene (15). This effect (fig 5) has been recognised for some time (16-18) and has generally been attributed to the catalytic action of zinc chloride formed during cross-linking of the polychloroprene (19). We have examined the effect of ZnO, ZnS, ZnCl2 and ZnS04 on the pyrolysis of polychloroprene and found that only zinc oxide results in the effects seen in fig 5. 

At the same time, we confirmed that ZnCl2 catalyses the dehydrochlorination of polychloroprene at temperatures below 200°C, but the reaction is very slow, and also accelerates on the evolution of hydrogen chloride by thermal degradation. The effect of ZnO has been observed in other chlorine - containing polymers including polyvinylidene chloride, chlorinated polyethylene and polyepichlorohydrin. The phenomenon thus seems unlikely to be a function of polymer structure. 

Polychloroprene is a family of synthetic mbbers, exhibits good chemical stability, and maintains flexibility over a wide temperature range. It is used in a wide variety of applications, such as laptop sleeves, orthopedic braces, electrical insulation, liquid and sheet applied elastomeric membranes or flashings, and automotive fan belts, and others. Subramaniam et al. studied the thermal degradation of polychloroprene mbber composites based on unmodified and ionic liquid modified multi-walled carbon nanotubes (MWCNTs), in aerobic and anaerobic conditions. They found that the polychloroprene mbber and its composite exhibit three and four... 

The allylic chloride moiety is the cure site for polychloroprene pol5uners (Fig. 2). The reaction of the labile allylic chlorides with bifimctional nucleophiles, metal oxides, or thioureas covalently joins interpolymer chains into a polymer network. The pol5uner cross-link density is proportional to the concentration of allylic chlorides on the polymer backbone. Thus mechanical goods with high modulus are made from polymers of high allylic chloride concentration. On the other hand, high levels of allylic chlorides decrease the thermal stability of polychloroprene polymers per mechanism described for thermal degradation of imsaturated diene polymer (56,57)... 

A copolymer of methyl methacrylate and vinyl chloride containing labelled chlorine ( "Cl) has been examined using thermovolatilization analysis and radiochemical assay. The yields of methyl chloride and hydrogen chloride agree with predictions made from sequence distribution calculations. The thermal degradation of a number of chlorine-containing polymers, poly(vinyl chloride), chlorinated polyethylene, chlorosulphonated polyethylene, polychloroprene, poly-epichlorhydrin, and co- and ter-polymers of epichlorhydrin has been compared and structural effects elucidated. ... 

Lehrle and co-workers [28] investigated the thermal degradation of polychloroprene at 387 °C using Py-GC-MS. The overall rate of production of volatile products was measured using total ion current (TIC) curves obtained from sequence pyrolysis investigations in which the products were not chromatographically resolved. These workers discuss the overall rate constants for polychloroprene determined by Py-GC-MS, the rate constants for the evolution of individual products, determined by the use of selected ion current versus time plots and the rate constants calculated from data obtained from further sequential pyrolysis experiments in which FID detection was used. The implications of the rate constant values obtained were assessed. 

Petcavich et al. (1978) employed IR subtraction techniques to elucidate the mechanism of the oxidative degradation of polychloroprenes at 60 °C. The spectra were taken at 60 2°C. The results lead to the conclusion that 1,2- and 3,4-structural irregularities are involved in the initial stage of the thermal oxidation of these compounds at 60 °C. In addition, a simple free radical mechanism seems to be consistent with the experimental results. The observed results suggest that polychloroprenes may be stabilized towards oxidative degradation by eliminating the 1,2- and 3,4-structures by chemical modification of the polymer after synthesis. 

Subramaniam, K., Das, A., HauBler, L., Hamisch, C., Stocfcelhuber, K.W., Heinrich, G. Enhanced thermal stability of polychloroprene rubber composites with ionic liquid modified MWCNTs. Polym. Degrad. Stab. 97, 776-785 (2012)... 

Hydrogen chloride evolution with polymer degradation did not occur readily at 120°C in a nitrogen atmosphere (96). At much higher temperatures (eg 275°C), the polychloroprene polymer was carbonized with HCl liberated by a non-free-radical mechanism (134). Polymer polymerized at low temperatures showed better thermal stability (93). 

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