A study of the photochemical decomposition of poly(isobutylmethacrylate)
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This present study was undertaken to obtain kinetic data on the photolytic decomposition of poly(isobutlyl-methacrylate) using a new technique of direct weight measurement during the reaction rather than the indirect pressure measurement systems previously used. The results obtained were used to fit the isobutyl ester into the pattern of information already obtained from the other members of the poly(alkylmethacrylate) series and in particular to determine whether a relationship existed between the Tg and the type of degradation reaction which occurs. The use of an adapted thermobalance to continuously register weight changes during degradation had a considerable advantage in terms of throughput of data, but, although producing information consistent with that obtained using more traditional methods could not compare in accuracy. The inherent lack of sensitivity of the thermobalance system and the appearance of a previously unreported local pressure phenomenon called the "thrust" effect produced results whose calculated error margin could cast serious doubt upon conclusions drawn from data obtained from all types of thermobalance work. The kinetic data obtained for poly(isobutylmethacrylate) indicated that the photodegradation reaction is random initiation followed by complete unzipping the overall Activation Energy for a sample of molecular weight 2. 71 x 10^6 being 42 kj mole^-1 and for a 5 -1 sample of molecular weight 3. 09 x 10^5 being 39 kJ mole^-1 Comparing these results with those obtained by Schoff¹⁰ for poly(ethyl) and methy-methacrylate) it is apparent that the reaction is not viscosity controlled because degradation takes place at temperatures well above the Tg and attempts to analyse the data using Schoffs equation proved unsuccessful.
Thesis, MSc Master of Science
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