Thermal stability, xxviii

Thermal analysis of PS, poly-p-methylstyrene and polyalpha-methylstyrene was carried out using evolved-gas analysis by IR and mass spectrometry and direct-pyrolysis analysis by mass spectrometric techniques. Evolved-gas analysis, both by IR and mass spectrometry, revealed features due mainly to the corresponding monomers or stable, volatile and low relative molec.wt. degradation products. In direct-pyrolysis mass spectrometry, however, primary decomposition products and heavier fragments such as dimers and trimers could also be detected. The ion-temp, profiles of the corresponding monomer ions revealed information about the thermal stability of the polymers. 25 refs. (XXVIII Colloquium Spectroscopicum Internationale, York, UK, June/July 1993)... 

The thermal stability of the nematic phase depends markedly on the position of the terminal cyano-group with respect to the polarizable (benzene) ring. For example, the clearing points are dramatically different (by 80 " C) for compounds (l.xxvii) (—25 °C) and (l.xxviii) (55 °C) [66, 67]. 

Okawara et cd. (42), reported that the addition of sodium N,N-dialkyldithiocarbamate to 1,2-dichloroethane (Scheme V) in DMF yielded a diadducl (XXVI) which could be cracked to produce S-vinyl-N,N-dialkyldithiocarbamate (XXVII). Monomer (XXVII) could be polymerized under free radical conditions, but it exhibited a high chain transfer constant so the molecular weight of the resultant polymer (XXVIII) was rather low. Furthermore, the thermal stability of the polymer was poor, which is not surprising since the polymer structure was very similar to diadduct (XXVI), which could be cracked at relatively low temperatures. Polymercaptan (XXDC) could be generated from (XXVIII) by treatment with dimethylamine. Polymers containing the dithiocarbamate moiety are report to be effective photosensitive resins (11,43). 

The monomer XXVIII is copolymerized with tetralluoroethylene to give a polymer-containing pendant fluorosulfonyl groups that are then hydrolyzed and acid exchanged to produce Nafion (XXIX) The resulting polymer combines the chemical, thermal, and oxidative stability of perfluorinated polymers such as polytetra-fluoroethy lene with the properties ofahighly acidic fluorinated sulfonic acid. Nafion is used in a variety of electrochemical applications such as the synthesis of chlorine and caustic and as the conductive membrane of many modern fuel cells. It has also been used in water electrolysis and as an acid catalyst in many proprietary commercial processes. 

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