Thermal degradation of polyisobutylene studied using factor-jump thermogravimetry

Abstract

The overall activation energy of the thermal degradation of polyisobutylene has been measured using factor-jump thermogravimetry to be 206 + 1 k J/mole over the range 365 to 405 ~ in N 2 at 800 mm Hg pressure and flowing at 4 mm/s over the sample. This is consistent with some values reported for thermal degradation in vacuum and in solution. In 5 mm Hg of N2, an apparent activation energy of 218 • 2 k J/mole was found, nnd in vacuum the apparent activation energy is 238 • 13 k J/mole. Troublesome bubbling made the vacuum values difficult to measure. Substitution of reasonable values for the activation energies of initiation, E i, termination, Et, and the activation energy, E a, for vacuum degradation in the equation Polyisobutylene (PIBu) has the formula -[C(CH3)2-CH2] n-and hence ideally contains no tertiary carbon atoms. Its thermal degradation in vacuum was studied by Madorsky and coworkers [1], who heated samples of PIBu to temperatures between 313 and 460 ~ and used mass spectrometry to characterize the fraction of degradation products volatile above -70 ~ Typically, this was 20 percent of the volatiles and was stated to consist of almost entirely of isobutylene. About 10 percent of the volatiles were thought to be dimer and trimer. The remaining 70 percent of the volatile material was assumed to be higher oligomers, with an average length of 9 to 10 monomer units, Earlier, Wall [2] had reported that 78 percent of the volatile products consisted of monomer when the decomposition was carried out at 400 ~ Using thermogravimetry to measure rates of volatilization at various temperatures in the range 306 ~ to 326 ~ , Madorsky and Straus [3] determined the activation energy of the in vacuo thermal degradation to be 49 kcal/mol (200 k J/mole).Inoue et al. [4] reported an activation energy of initiation of 41 kcal/mole (170 k J/mole) and an average chain length of 30 for thermal degradation of PIBu above 280 ~ Slobodin and Matusevich [5] found the products of PIBu which had been decomposed thermally at 325 to 400 ~ to be 49 percent isobutylene, ~ 1 percent isobutene and isopentane, 17 percent C 8 hydrocarbons, 18 percent C12 hydrocarbons,

Comparison of literature models for volatile product formation from the pyrolysis of polyisobutylene at mild conditions: Data analysis, free-radical mechanistic considerations, and simulation of initial product-forming pathways

“…T-ramped TGA studies at 20 8C min À1 reveal the onset of weight loss at %350 8C and its completion by %425 8C with negligible residue [4,12,13,23]. Isothermal TGA studies have monitored weight loss [3b-3e,3g, 7,12,13,18,24], extent of formation of volatiles [6d,6e,6g], or pressure increase [14].…”

Thermal analysis

“…The overall E of the thermal degradation of polyisobutylene, measured using factor-jump TG, was 206 ± 1 kJ/mol at 365-405°in N (29). Furifural-8-hydroxyquinoline copolymer was characterized by TG and IR (114).…”