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The calorimetric determination of the ceiling temperature for the chemical polymerization of pyrrole
Implications on the electrical conductivity
Abstract
The previously found strong dependence of the polymerization enthalpy on the reaction temperature has been rationalized. The temperature dependence is to be ascribed to the existence of a ‘ceiling temperature’ for the polymerization process of the pyrrole monomer. The determined ceiling temperature has beenT≊350 K when FeCl3 was used as the oxidizing agent in CH3CN solution. The existence of a ceiling temperature together with its already determined exoenthalpic nature allows to classify the polymerization reaction as an exoentropic one. From the dependence of the yield of insoluble polymer on the reaction temperature, the trend of the relative mean numeral molecular massM n for the different obtained polymers has been determined. Measurements of electrical conductivity on pressed pellets of the different polymers allowed to establish a correlation between theM n value and the conductivities The dependence of the conductivity on the exposition time to the air allowed to do some essays on the aging behaviour of the obtained polypyrrole. By making some assumptions, an absolute calorimetric determination of the value ofM n of polypyrrole was tempted together with that of the related poly-N-vinilpyrrole.
Abstract
Attempts are made to use kinetics parameters from thermal decomposition experiments at high temperatures to predict service lifetimes of polymeric materials at lower temperatures. However, besides the obvious measurement and extrapolation errors (which can be considerable), there are two fundamental reasons why quantitative long range extrapolations can not be made for complex condensed phase systems. They are: 1) Arrhenius kinetics parameters can not be extrapolated through phase transitions or softening temperatures; 2) Arrhenius kinetics parameters can not be extrapolated through the ceiling temperature region. Satisfactory lifetime prediction methods can be developed only after a thorough analysis of the causes of service failure. A real method has been taken from literature to illustrate the correct procedures.
Abstract
Adiabatic calorimetry is a technique that has been introduced as an important approach to hazard evaluation of exothermically reactive systems. In this paper the free radical polymerization of methyl methacrylate (MMA) has been studied. One of the most important aspects of MMA polymerization is its exothermicity and autoaccelerating behaviour, these characteristics can generate the occurrence of a runaway reaction.In a runaway situation the reacting system is close to adiabatic behaviour because it is unable to eliminate the heat that is being generated. An even worse situation can be reproduced in the laboratory with the Phi-Tec pseudo-adiabatic calorimeter. Process design parameters that are usually calculated from thermodynamic data or using semiempirical rules, such as adiabatic temperature rise or maximum attainable pressure, can be directly determined.The existence of the ceiling temperature has been experimentally demonstrated.
Adiabatic thermokinetics and process safety of pyrotechnic mixtures
Atom bomb, Chinese, and palm leaf crackers
Process safety Fireworks mixtures are vulnerable to thermal hazards. ARC data are used for determining the ceiling temperature for processing, handling and transportation of hazardous materials. Accordingly, the practice adopted is that the
of iPP facilitates the formation of α-iPP, but weakens the formation of β-iPP. In the case of iPP/MSW, the ceiling temperature for the formation of β-iPP was observed above 138 °C, whereas for the iPP/MSW/PP-g-MAH composite, the critical temperature
