Glass transition temperature Gibbs-DiMarzio theory

Fig. 6. The hole formation energy 2ajk), the barrier to internal rotation (/de/fi) and the glass transition temperature vs. compoafdon for NaPOjijCa(PO, counterion copolymers (2 /ft) and (Aelk) calculated from the Gibbs-DiMarzio theory at 10% intervals. T, points experimental...

Figure 5-8. Molecular weight trends in the glass transition temperature trends in cyclic and linear oligomers of poly(dimethyl siloxane), and the comparison of these data with the prediction of the Gibbs-DiMarzio theory. [Reprinted with permission from E. A. DiMarizio and C. M. Guttman, Macromolecules, 20, 1403 (1987). Copyright 1987, American Chemical Society]...

Over the past 30 years a number of theories have been developed to account for the variation in the glass transition temperature (Tg) of polymeric materials as a function of molecular weight (MW). Three of the most notable of these approaches have included the straight line technique of Fox and Flory and the statistical mechanical theories of Gibbs and Gibbs-DiMarzio (G-DM). Because of the universal applicability claimed for the latter approach, the G-DM theory has received considerable attention. " ... 

Proposed by Gibbs and DiMarzio, this theory considers that the glass transition temperature of a given polymer corresponds to the value at which a given chain exhibits only one unique conformation. 

Another interesting aspect of the Gibbs-DiMarzio " " theory is that it predicts an effect of deformation on the glass transition temperature due to changes in the entropy of the system upon straining the network. For uniaxial extension, the result in terms of the small-strain modulus G, measured at a temperature Tq, is ... 

The entropy theory of the glass transition was developed by Gibbs and DiMarzio and by Adams and Gibbs to describe polymeric systems. By mixing the polymer links with holes or missing sites on a lattice to account for thermal expansion as in a lattice gas model, they could determine the entropy of mixing and the configurational entropy of the polymer. They found a second-order transition at a temperature They then pointed... 

---