Factors affecting the thermal stability of polytetrafluoroethylene

Abstract

The structure and kinetics of thermal decomposition of polytetrafluol'oethylene suggestcd sev eral m ethods for impro vemcnt of its stability: (a) p olym crization in the presen ce of fluor oca rbo~l catalysts or ph<;>to?hemically to eliminate labile centers for initiation. (b) incluSlOn of foreIg n structural UllitS III the polymer to promote chain t ransfer of t.he free radicals active in d epolymcrization, (c) inclusion of foreign m olecules capable of promoting chain transfer . . The catalysts t ri ed inclu?ed perfluorodimeth ylmcrcury, perfluoromethyl iodide, and fl uorme gas, as well as convent.lOnal catalysts. The foreign structural units and a dditiv~s included .sulfur, seleni um, and a vari ety of hydrocarbon and fluorocarbon groups, maml.y aromatIC, addcd usuall y as dibromides to t he polymerizing mixtme. None of thc cxpeflmental catalysts or additives brought about any change in the rate of thermal d ecomposition.

The Decompostion of Polytetrafluoroethylene in a Glow Discharge

“…(3) The discharge is sustained by C2F4+ and CF+ ion formation reactions. (4) The major gaseous product, C2F4, is formed from the combination of CF2 radicals. (5) Radical disproportionation reactions account for the presence of carbon and the F or F~.…”

“…The data support a hypothesis which includes unzipping via CF2 radicals, polymer formation via C2F4 excited species, CF2 radical disproportionation to account for the F species, and oxidation of C2F4 excited species to give COF2.The kinetics, mechanism, and thermodynamics of the thermal decomposition of polytetrafluoroethylene (PTFE) has been studied by a number of workers. [1][2][3][4][5][6][7][8][9][10][11][12][13] The results of these investigations can be briefly summarized by saying that in the temperature range from 360 to 600°, the reaction is of the first order with tetrafluoroethylene being the primary product. The mechanism involves rupture of carbon-carbon bonds followed by the unzipping of the resultant radicals.Only a few of the cited references give analytical data for the composition of the gaseous products resulting from the depolymerization reaction.1-3•7 The products reported include CF4,C2F4,C3Fe,C4F8, SiF4, C02, and CO. Of these, only C2F4 and C3F6 are confirmed by all investigators.In the present work, PTFE was decomposed in the presence of a microwave-excited glow discharge.…”

“…The kinetics, mechanism, and thermodynamics of the thermal decomposition of polytetrafluoroethylene (PTFE) has been studied by a number of workers. [1][2][3][4][5][6][7][8][9][10][11][12][13] The results of these investigations can be briefly summarized by saying that in the temperature range from 360 to 600°, the reaction is of the first order with tetrafluoroethylene being the primary product. The mechanism involves rupture of carbon-carbon bonds followed by the unzipping of the resultant radicals.…”

Pyrolysis of fluorocarbon polymers

“…From the variation of rate with molecular size one can sometimes deduce whether the initial cleavage is at the end or at random along the chain. For polytetrafluoroethylene, studies of this type have so far been inconclusive, the rate being independent of molecular size [ 4 , 6 , 28 ]. Numerous polymers of tetrafluoroethylene prepared in various ways with various catalysts, including fluorine gas, all have essentially the same rate of volatilization [ 4 ].…”