Polymer-Melt Viscosity and the Glass Transition: An Evaluation of the Adam–Gibbs and the Free-Volume Models

Abstract

The Adam–Gibbs and the free‐volume theories of polymer‐melt viscosity and the glass transition are applied to the infinite polymethylene chain by comparing the exponential terms in the respective viscosity equations: 2.3B / (T − T 0 ) = C / TS c = b / φ . It is shown that the configurational entropy S c and the free volume φ , which apply in these equations, constitute only a portion of the thermodynamic “excess” liquid entropy and volume. In an alternate form of the A–G equation: C / TS c = Δμz* / RT , if Δμ is identified as 2.3BR, z g * turns out to be equal to the “activation volume” expressed as monomer segments at T g . In the Adam–Gibbs context, the glass transition is assumed to be characterized by the constant: z g *S cg = 5.5 e.u. On this basis, a value of S c is derived for polystyrene at T m which agrees with independent estimates. Values of the A–G and the free‐volume parameters are reported for (CH2)∞, polystyrene, and polyisobutylene, and relationships between S c and φ are presented.