Regression analysis studies of polymer transitions II. TII from specific heat and other data for polyisobutylene

Linear regression analysis studies with residuals of heat capacity vs. temperature ( C p vs. T) data above the glass transition temperature ( T g ) 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 T ll transition (relaxation); the upper one an intramolecular T lp 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). T ll is confirmed by thermal diffusivity, differential scanning calorimetry (DSC), 13 C nuclear magnetic resonance (NMR) spectroscopy and the T * temperature of Lobanov and Frenkel based on Arrhenius‐type plots log frequency vs. 1/ T g . A comparison of dynamic mechanical loss data, both old and new, reveal that T ll follows a Vogel‐WLF type relation; log f vs. 1/( T 0 −1/ T o ). 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 T u . A considerable amount of literature data long neglected from the viewpoint of its bearing on T ll is reviewed. T ll has been observed in the same way as T g 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 T ll in PIB, it cannot be dismissed as an artifact. A molecular origin for T ll 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 10 10 Hz and temperatures from 150 to 500 K. It shows T β , T g , T ll and methyl group rotation, all based on data in the literature. The molecular weight dependence to T g and T ll and the low resiliency of butyl rubber as it relates to T ll are discussed in the appendices.