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.
Samples of cotton , cotton h ydrocelJulose, and viscose rayo n, both by t hemselves an d impreg nat;ed with sod ium carbonate or sodium chloride, were p yl'Olyzed at 250 0 to 397 0 C in a lli g h vacuum. The volatile products were fractionated a nd t he fractio ns analyzed in th e m ass spectrometer a nd by inf rared absorpt ion. Th e volatile fraction s co nsisted mainly of CO, CO2, water, and levoglucosan (tar). The residue consisted main ly of carbon (cha r).Imp reg na t ion of the cellulosic m aterials with salt s caused a decrease in t he y ield of tar and an increase in t he yields of CO, CO" H 20 , a nd char. R ates of thermal degradation of the sam e materials were in vcstigated in the range 245 0 to 305 0 C by a loss-of-w eight m ethod, usin g a ver y sensitive t ungste n spring bala ncc enclosed in a vac uum. Plots of rates of loss of " 'eigh t versus percentage of loss of ' weight, in t h e case of pure cellulosic materials, p ass th rough maxima at a bout 13 to 23 percent loss of " 'eigh t, t he n drop graduall y to t he carb onization end point. In the case of sampl es impreg nated with sodium carbonate or sod ium chlorid e, t he initial ra tes of loss of weight are very hi gh , but drop rapidly to the carbon izatio n end p oi11 t . Th e activation energies o f thermal d egradation of t h e pure cellulosic mater ials are much greate r than t hose of t he sa me material s impregnated with sod ium carbo nate or sodium ch lor ide .
Fortisan, cellulose triacetate, and NOroxidized cellulose were pyrolyzed in a vacuum in the temperature range 180 0 to 465 0 C. Cotton cellulose and cellulose t ri acetate were also pyrolyzed in nitrogen at atmospheric pressure. The tar yields were in the decreasing order from: Cotton, Fortisan, cell ulose triacetate, and oxidized cellulose. The other volatiles consisted mainly of acetic acid, carbon dioxide, and carbon monoxide, from the triacctate; and water, carbon dioxide, and carbon monoxide from the other celluloses. In all cases there was a carbonaceous residue (volatilization end point), the amount depending on t he natur e of the cellulose and the temperature of pyrolysis. When pyrolyzed in nitrogen at atmospheric pressure, cotton cellulose and cellulose triacetate yielded less tar than when pyrolyzed in a vacuum. T he tar from cellulose triacetate consisted of a compound whose infrared spectrum resembled that of the original triacetate. Cotton cellulose, Fortisan, and cellulose triacetate do not differ much in t heir initial rates and activation energies of thermal degradation. Oxidized cellulose has very high initial rates of therm al degra dation .
Recently the depolymerization of addition polymers has been treated in terms of four elementary reactions: initiation, propagation, transfer, and termination; analogous to those reactions which operate in the polymerization process. It is the transfer process which, according to its relative importance, gives rise to differences in polymers in the monomer yield, in the rate vs. conversion behavior, and in the molecular weight vs. conversion behavior. The transfer process is assumed to operate through the abstraction of a hydrogen from the polymer chain by a radical. By substituting a deuterium for the hydrogen at selected points in the polymer chain, the amount of the transfer process should be decreased due to an isotope effect. Two deuterated polymers were made from α‐ and β‐deuterated styrenes and their depolymerization behavior studied. In the case of the α‐deuterostyrene polymer the results are compatible with a ½ decrease in the rate of the transfer process and also an increase in the rate of the propagation. The results with the β‐polymer imply an increase in both the transfer and propagation rates. The data obtained indicate that in polystyrene the intermolecular transfer process is mainly responsible for the fall in molecular weight of the polymer residue during depolymerization.
Molecular weights of polymer residues from the thermal degradation in vacuum of two polymethyl methacrylate samples, one polymerized with benzoyl peroxid e and the other without an y initiator, have been obtained over wide extents of degradation at various constant temperatures. A linear relation, dependent upon the temperature but i ndependent of rate of volatilization and rate of change of l /M w , is found when log R is plotted against l /M w • (R = ratio of residue weight to original specimen weight, and .Mw= weight-average molecular weight. ) The results are explained on the basis of a free-radical chain-reaction mechanism in which intermolecular chai n transfer (activation e nergy = 29 kilocalories) is the primary, or perhaps the sole, cause of the molecular-weight decrease.
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