Free volume excess

How do we take into account the contribution of dangling chains to Tg In linear polymers, we know that chain ends carry on a free volume excess and, thus, play a plasticizing effect that can expressed through a copolymer law ... 

Even when using LDPE and PP, the diffusive losses of most nonpolar solvents may be unacceptably large for A designs that exceeded 1 cm . This is especially true at higher exposure temperatures because both solute diffusion and polymer free volume increase with temperature (Comyn, 1985). Even when solvent losses were not excessive, uptake of HOCs by membrane-enclosed solvents appeared to become curvilinear well before thermodynamic equilibrium was approached. This phenomenon is likely due to the outward flux of sampler solvent with elevated HOC levels (relative to water), which appears to facilitate residue... 

Tanaka et al. have studied the surface molecular motions of PS films coated on a solid substrate by lateral force microscopy and revealed that the Tg at the surface was much lower than the corresponding bulk one [148]. Possible reasons for this included an excess free volume induced by localized chain ends, a reduced cooperativity for of-relaxation process, a reduced entanglement, and a unique chain conformation at the surface. For comparison, they examined surface relaxation behavior of high-density PMMA brushes. 

Endless discussion exists regarding whether a theory based on the configurational entropy or the excess free volume 8v provides the more correct description of glass formation. Thus, this section briefly analyzes the relation... 

Figure 15. The LCT configurational entropy s T (normalized as in Fig. 11) as a function of the reduced specific volume 8v = [v T) — v(T = To)]/v(T), which is a measure of the excess free volume in the polymer system. Different curves refer to the F-F and F-S polymer fluids and to low and high molar mass polymer chains.

The solid phases of 81 are also well ordered macroscopically and their higher E/C ratios require that the hydroxy-1,4-biradical be in rather inflexible reaction cages with little excess free volume. Hydrogen bonding to neighboring ketone molecules may be partially responsible for the high photoproduct ratios found upon collapse of the biradicals in the solid phases, but the size, shape, and flexibility of the reaction cavity are clearly the more important factors. The highest E/C ratios observed in the second solid phase of 81a... 

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