ISSN:
0021-8995
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
Linear regression analysis studies with residuals of heat capacity vs. temperature (Cp vs. T) data above the glass transition temperature (Tg) for polyisobutylene (PIB) of molecular weights M¯v = 1,350,000 and M = 4900 show that the data points can be represented by three straight lines in each case. The lower intersection temperature represents the intermolecular Tll transition (relaxation); the upper one an intramolecular Tlp process. Both processes are confirmed by ultrasonic velocity data in vulcanized butyl rubber, by zero shear melt viscosity data in PIB (M = 4900); and by isothermal specific volume vs. pressure data in PIB (M¯v = 36,000). Tll is confirmed by thermal diffusivity, differential scanning calorimetry (DSC), 13C nuclear magnetic resonance (NMR) spectroscopy and the T* temperature of Lobanov and Frenkel based on Arrhenius-type plots log frequency vs. 1/Tg. A comparison of dynamic mechanical loss data, both old and new, reveal that Tll follows a Vogel-WLF type relation; log f vs. 1/(T0 -1/To). PIB samples with number average molecular weights between 7100 to 860,000 have been measured on three types of support systems: glass braid (0.3 Hz), filter paper (11 Hz), brass shim stock (14-16 Hz), and give similar values of Tu. A considerable amount of literature data long neglected from the viewpoint of its bearing on Tll is reviewed. Tll has been observed in the same way as Tg by both relaxational and quasi-static methods. Some instructive cross comparisons between these two types of methods emerge. With so many diverse methods yielding evidence for Tll in PIB, it cannot be dismissed as an artifact. A molecular origin for Tll is plausible in terms of the Frenkel-Baranov phase dualism mechanism. A complete relaxation map (log f vs. 1/T) has been assembled with frequencies from 10-2 to 1010 Hz and temperatures from 150 to 500 K. It shows Tβ, Tg, Tll and methyl group rotation, all based on data in the literature. The molecular weight dependence to Tg and Tll and the low resiliency of butyl rubber as it relates to Tll are discussed in the appendices.
Additional Material:
17 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/app.1986.070320323
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