A selected group of standard atactic polymers with CC, CO, diene, and SiO backbones and some crystalline polymers for which an amorphous phase T(g) is known have T(g)'s which increase with the product of cohesive energy density (CED) times the characteristic ratio (C infinity), falling on either of two straight lines of positive slope, intersecting at T(g) = 118 K. The principal difference between polymers on the two lines concerns their low-frequency mechanical relaxation spectra: upper line polymers tend to have a relatively strong T(beta) approximately 0.75T(g) but weak or missing T(gamma) < T(beta); those on the lower line show a weak or missing T(beta) and a strong T(gamma) arising from side-group motion about the C-R bond. This motion appears to generate extra free volume in the glassy state for the lower-line polymers compared to those in the upper line. All polymers follow the conventions DELTAalphaT(g) = 0.113 and alpha1T(g) = 0.164. Polymers with longer side chains, i.e., poly(n-butyl methacrylate), poly(ethyl acrylate), and polybutene-1, no longer lie on their respective lines. Many prior studies may have failed through inclusion of polymers of diverse structural types, i.e., in-chain rings, cellulosics, long side chains, etc., in addition to the basic standard polymers selected herein and generally included in some earlier studies. CED X C infinity may be thought of as the product of a persistence length times an intermolecular force.
