Polytetrafluoroethylene, from pyrolysis

ANALYSIS OF VOLATILE PRODUCTS FROM PYROLYSIS OF POLYTETRAFLUOROETHYLENE AT ELEVATED TEMPERATURES IN A VACUUM [255]... 

The first report of the cyclodimerization of fluorinated olefins was provided by Lewis and Naylor,3 working at E.I. DuPont de Nemours Co., in 1947. While studying the pyrolysis of polytetrafluoroethylene (PTFE), the compound octa-fluorocyclobutane was isolated from the pyrolysis off-gas stream. The researchers identified the product and speculated that it was formed by the cyclodimerization... 

The vacuum pyrolysis of thin samples of polytetrafluoroethylene follows first-order kinetics with monomer as the major decomposition product in the temperature range from 360—510° C (Siegle, Muus, and Lin). The rate constant does not depend on either the molecular weight or the type of polymer and is characterized by an activation enthalpy of 83.0 kcal/mole and a frequency factor of 3 x 1019 sec-1. The melt viscosity decreases during pyrolysis. 

Active carbons are obtained by partial combustion and foermal decomposition of various raw materials followed by carbonization and activation. A detailed look at the process of pyrolysis and carbonization of a parent feedstock and the processes of generation of an isotropic porous carbon and its activation illustrates the complexity of reactions involved in its manufacturing. Active carbons are manufactured from a wide variety of materials wood [1, 2], coal [1, 2], bituminous coal [29], rubber [30, 31], ahnond shells [32], oil-palm stones [33], polymers (e.g., vinylopyridine resin [34] and polytetrafluoroethylene [35]), phenolic resins [36], rice husk [37], etc. Very interesting active carbon honeycomb structures were fabricated from combination of synthetic precursors, i.e., phenolic resins, along with several organic and inorganic additives [38]. 

Arenes from Aliphatic and Allcyclic Precursors. —The formation of perfiuoromesityl-ene and perfluoropseudocumene by pyrolysis of polytetrafluoroethylene at 530— 560 °C over metal catalysts (Vol. 2, p. 359) has been patented,and improved yields of cyclic aromatic trimers have been obtained by coupling reactions of perfluoro-(l,2-di-iodocyclo-butene and -pentene) (see p. 74). i The formation of polyfluoronaphthalene derivatives from one of the bicyclic compounds (24) obtained during the reaction of carbon tetrachloride with 3,3,4,4-tetrafluorohexa-... 

Pentafluoropyridine, although reported to be stable when pure at 550—600 °C, has been found to react at these t nperatures with potassium fluoride and with polytetrafluoroethylene to afford a moderate yield of perfluoropicolines (see Vol. 1, p. 256), typically a mbcture of the 3-isomer (88%) and the 2-and 4-isomers (6%). The reaction is thought to involve a difluorocarbene intermediate (Vol. 1, pp. 187, 256) formed by the decomposition of the <7-complex of the pyridine and potassium fluoride, or from the pyrolysis of polytetrafluoroethylene. Both 4-methoxy- and 4-nitro-tetrafluoropyridines... 

Z)-haloalkenylsilanes afford (Z)-dihaloalkenes], Acetylenic alcohols (122) react with trimethylsilyl iodide to give di-iodoalkenes or unsaturated iodohydrins, depending on the alcohol used. Terminal acetylenic alcohols react cleanly to afford the unsaturated iodohydrins (123) whereas internal acetylene precursors give mixtures of di-iodoalkenes where (124) predominates. Tetrafluoroethylene is conveniently prepared, in excellent yield, from polytetrafluoroethylene by vacuum pyrolysis. ... 

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