Pyrolysis of polyisobutene (Vistanex), polyisoprene, polybutadiene, GR-S, and polyethylene in a high vacuum

Abstract

amples of polyisobutene, polisoprene, polybutadiene, GR-S, and polyethylene, weighing about 25 to 50 milligrams, wcre pyrolyzed in a vacuum of about 10-6 millimeter of mercury in a specially designed apparatus at temperatures ranging between 300 0 to 475 0 C. The volatile products of pyrolysis were separated into four fractions: (IV) gaseous, volatile at -196 0 C; (IlIA) liquid, at -75 0 C; (IlIB) liquid, at 25 0 C and (II) wax-like fraction , volatile at the temperature of pyrolysis. The gaseous fraction was analyzed in the mass spectrometer and was found to consist in all cast'ls of CH4• The liquid fraction, I lIA, was analyzed similarly and was found to give a mass spectrum characteristic for any given polymcr. A molecular weight determination of the wax-like fraction by the microfreezing-point-lowering method, showed it to vary from 543 to 739, dtlpending on the polymer from which the fraction was obtained. It is shown that the method of pyrolytic fractionation of high molecular weight polymers, in conjunction with mass spectrometer analysis of the more volatile fractions, can serve as a means of identifying the polymers.

Pyrolysis of styrene, acrylate, and isoprene polymers in a vacuum

“…Rast's method [81 was checked by the present authors on a number of pure compounds. The results of this check, with C6H12 and C6H 6 as solvents, were reported previously [2]. In checking this method the values used for F, the molecular freezing-point lowering, were 20.0° and 5.12° C for C6H12 and CeR6' respectively.…”

“…Fract ion III is very small and, on the average, amounts to 5.9 ± 0.6 p ercent of the total volatilized part. In this resp ec t it resembles polyethylen e, where fraction III is 3.4 p er cent [2] . A quantitative analysis of frac tion III could not .be ob tained in the mass spectrometer b ecause of lack of mass spectra of some of the componen ts.…”

“…Pyrolysis of polyisoprene has been described in a previous paper [2]. The investigation has now been extended to include the isoprene-dipentene ratio in the volatile products.…”

“…The molecular still used for the pyrolysis of polymers in this investigation was the same as was used in the previous work [1,2]. It consists of a Dewarlike Pyrex-glass apparatus made of two concentric parts jointed by ground waxed flanges.…”

“…To facilitate further t he m ass-spectrometer analysis, fraction III in som e cases was again fractionated into a lighter fraction lIlA, containing mostly the monomcr-size fragments, and a h eavier fraction lIIB , containing mostly th e dimer-size fragm en ts. Separa tio n in to lIlA and IIIB was carri ed out at -80 0 C by a method describ ed in a previous pllblicaLion [2]. Composition of IlIA and lIIB was deLermined by m ass-spectrometer analysis.…”