Thermal degradation of tetrafluoroethylene and hydrofluoroethylene polymers in a vacuum

Abstract

T e fl on and tetrafluoroethyle ne photopolymers, on py rolysis in a vacuum at 423.5 0 to 513.0 0 C, yield almost J 00 per ce nt of monom er. The r ate of formation of monome r at a n.,· given tem p e rat ure fo llows a first-order react ion and is independe nt of t he method of pre pa ration of poly mer or its initial ave rage molecu lar weight. The activation energy was determined by a press ure method and a wei gh t met hod , and a value of 80.5 k cal was found b.'· both methods . A prelimina ry heating of Teflo n in air a t 400 0 to 470 0 C did not change a ppreciably its rate of degradation into mono me r when it was s ubseque ntl y heated in a yacuum . Polyvinyl fluorid e, 1,I -polyv in y li dene fluorid e, and polytrifluo roethylene were pyr olyzed in t he range 372 0 to 500 0 C. The volatiles consisted in all cases of HF and a wax-lik e mate rial co nsisting of chain fragments of low volatili ty. P olyvinyl fluoride and polyt rifl uoroet hyle ne deg rade to co mplete volatilization, whereas 1,1-poly viny li dene fluoride becomes stabilized at about 70-pe rcent loss of we ig ht. The rate-of-volat ilization curves indicate a fi l'st-o rder reaction for poly vinyl fluo ri de, a zero-order reaction fo r t riflu oroethy le ne, alld an undeterm in ed ord er for 1,1-polyvinyli dene fluoride. The orde r of t hermal s tabili ty for t hese poly me rs, as com pared with polymet hy lene, is as follows: Poly vin yl f1uoride < poly me th,vle ne < polyt riflu oroethylene < ] . J -polyvi nylidene f1uor idc < polytetrafluoroeth ylene.

Factors affecting the thermal stability of polytetrafluoroethylene

“…Most of the monomer was prepared by pyrolysis of Teflon polymer at 650 0 to 700 0 C and 1 mm, using the method of Lewis and Naylor [8] with minor changes. Contrary to expectations based upon the r esults of these authors at moderate pressures, a small percentage of higher fluorocarbons appears to form even at pressures of a few microns [9] . In distilling t he monomer into polymerization tubes, a small tail fraction, roughly 20 percent, was rejected.…”

“…The pyrolysis data given in table 6 are from the work of Madorsky, Hart, Straus, and Sedlak, full details of which are included in their report [9] . The product of pyrolysis was nearly pure tetrafluoroehylene.…”

“…Polyethylene decomposes appreciably, 0.16 percent p CI' minute at 385 0 C; poly tetrafluoro ethylene decomposes at the same rate at 489 0 0, only 104 deg higher [9,25]. For comparison, bond-dissociation energies in related simple molecules are: for C2H 6 and other lower paraffin , C-C = 80 kcal, C-H = 101 kcal ; for C2F 6 , C-C = 124 kcal, C-F = 107 kcal.…”

Thermal degradation of polyacrylonitrile, polybutadiene, and copolymers of butadiene with acrylonitrile and styrene

“…The hydrogen cyanide most likely forms by spli tting-off the chain in the same manner as CH3COOH in the pyrolysis of polyvin yl acetate [11], H Cl in tbe pyrolysis of polyvinyl chloride [12], and HF in the pyrolysis of hydroAuoroethylene polymeTs [13]. Formation of monomer can b e visualized as follows.…”

Pyrolysis of cellulose in a vacuum

“…Fraction V-so, volatile at -80° C, but not at -190° C. 5. Fraction V -19o, volatile at -190° C.5 'In previous ,york [5] on pyrolys is of polymers, fraction s V PY', V", V-so, and V -I90 were design ated as [! 'actiOllS II , IIIB , lIlA, and IV , respectively.…”