Several ~uorocarbon polym~rs ~ere irradiated with Co60 gamma radiation at doses up to 10 22 ev/g. ~he polymers studIed Included polytetrafiuoroethylene, polytrifiuoroethylene, polychlorotrIfiuoroethy.len~, a copoly.mer of tetrafiuoroethylene with hexafiuoropropylene, and several rubbery vInylIdene fiuorIde copolymers. G-values were measured for volatile p~oducts, for free radica.ls ~etected by electron spin reso~ance, and, in the case of polychlorotrIfiuoroethylene, for SClSSIOns. The course of degradatIOn or crosslinking was followed by zero-strength-time .and tensile-strength measurements. It was found that for poly tetrafiuoroethylene and Its hexafiuoropropylene copolymer the presence of air-accelerated scission drastically. The mechanism of the radiation-induced changes is discussed in terms of freeradical intermediates.
The electron spin resonance spectrum of hydroxyl radical, generated from titanous ion and hydrogen peroxide in a flow system, was studied as a function of flow rate, temperature, and mixture composition. Two peaks occur: a principal peak at g = 2.0128 and a usually minor peak at g = 2.0114. The intensity of the minor peak is increased by large concentrations of titanous chloride or sulfate, increased slightly by large concentrations of titanic salts, and lowered by excess sulfuric acid. The minor peak is thought to be the spectrum of hydroxyl associated with titanic ion. At 20 and 28°the concentration of hydroxyl shows a maximum as flow rate is varied, while the concentration increases monotonically with increasing flow rate at 58°. At low flow rates (time after mixing 0.5 to 4 sec.) there appears to be an approach to second-order disappearance with k -4.5 X 105 -1 sec.-1 at 28°a nd an activation energy of 11 kcal./mole (46 kjoules/mole).
During recent yea rs a co nsid erable nurnber of t heo retical a nd exp erimental stud ies have been published o n t he kin etics and mechanism of t he t hermal d eco mposition of poly mers. The tr eatment of depo. lymerization as a free-rad ical chain reaction involv ing t he four basic steps of initiation, p ropagation, t ra nsfer, and termination seems ad equate for a fairly complete und erstandin g of the p rocess in a la rge number of cases. Ra te data now available a re disc ussed from t his poin t of view. It is shown t hat most of t he characteristics of t he t herma l d eco mposition rate cu r ves a re a r esult of t heir basic struct ure and not of trace impuri t ies. Th e mag nit ud e of the rates a nd act.ivation energies are, however, sens it ive to trace stru ctures o r impuri t ies. It is shown t hat in ter molec ula r transfer will account for the rate behavior in a large number of poly mers. In a relatively few other cases in t ram olecula r transfer is indi cated to bc of more importan ce.
(Dece mber 22, 1965) T he rate of decom lJOsition of pol ytetraAuoroethylene, exposed to gamma radiation in a Aowing helium at mosp here, was studied in th e range of te mperatures 330 to 450°C, dose rates 0.1 to 7.6 MR/h, and sa mp le thi c kn esses 0.0006 to 0.01 e m. Rate meas ureme nts were made with a the rmal co nductivity ce ll in th e exit strea m, which recorded essentially th e diffe re nce between the thermal and radiation· ind uced rate, in total molec ul es of volatiles per seco nd. At te mpe ratures below about 400°C, th e vo lati le products were a complex mixture. Above 400 °C, tetraAuoroethylene was the major product, and the radiation·induced rate had a n activation e nergy' of 70 to 84 kJ / mol. The radiati on-indu ce d rate is proportional to square root of dose rate, after appropriate allowance for the thermal in itiat ion is mad e. Analysis of the res ult s s ugges ts that th e rate of th e the rmal initiation has a very hi gh preexpone ntial factor, 10'" to 10"0 s-' . Th e activation e ne rgy [or te rmination is large, E. > 155 kJ/ moJ. Diffus ion and reverse reaction appear to be minor fac tors above 400 °C, but a surface reaction may be important. Th e th ermal decomposition mec hani sm see ms dearly to co ns ist" of rand om initiation, termination by bimol ec ular reco mbinati o n and a short kinetic c hain (13 at 480°C).
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