Effect of molecular weight on formation of non-volatile oligomers by thermal degradation of polyisobutylene and its kinetic analysis

✍ Scribed by Takashi Sawaguchi; Tadashi Ikemura; Manabu Seno

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 812 KB
• Volume: 37
• Category: Article
• ISSN: 0032-3861
• DOI: 10.1016/s0032-3861(96)00357-6

✦ Synopsis

The formation of functional groups of non-volatile oligomers by the thermal degradation of polyisobutylene is characterized by a kinetic approach including intermolecular hydrogen abstraction of primary (p) and tertiary (t) terminal macroradicals (Rp and Rt) and volatile small radicals (S°), followed by 3-scission. By assuming in the kinetic analysis that the reaction occurs competitively under a steady state regarding the onchain macroradicals, various composition ratios for the functional groups can be represented in terms of the rates of respective hydrogen abstraction. The ratio between the tert-butyl endgroup (t-Bu) and the isopropyl endgroup (i-Pr), which corresponds to that between the abstraction rates of Rp and R~, is expressed by the product of the rate constant ratio and the integrated macroradical concentration ratio ([R~]/[R~]). The observed value of the ratio [t-Bu]/[i-Pr] decreases with reaction time. This is induced by a decrease in the molecular weight (M) of the reaction medium. The molecular weight dependence

The value of exponent a was determined to be about 1.2 and 0.7 at 300 and 320°C, respectively, from the analysis of data at various reaction times. These values are roughly consistent with average values (1.0 and 0.9) of the same power-law exponent for the volatile oligomers. These results support the hypothesis that the concentrations of the respective radicals decrease in different ways.