Glassy polymers history effects

Hodge, I. M., and Huvard, G. S. (1983). Effects of annealing and prior history on enthalpy relaxation in glassy polymers. 3. Experimental and modeling studies of polystyrene. Macromolecules 16(3), 371-375. 

Effects of Thermal History. One of the most useful and fundamental parameters defining the state of a polymer is its enthalpy (or specific heat). Considerable evidence has been adduced to show that the thermal characteristics of glassy polymers such as PC are sensitive to thermal... 

The reptation idea could account for the effect of polymer molecular weight and solvent concentration on the dissolution rate. However the key concentration identified in this approach [57,59] is one at the surface. This implies independence of the solvent concentration history. This may not be true as the disentanglement of polymer chains does not commence till the local solvent concentration is greater than a critical value at which the local glass transition temperature is lowered below the experimental temperature so that the glassy polymer changes into a gel. Also, all of the efforts discussed so far failed to take into account the effect of the viscoelastic properties of the polymer on the dissolution mechanism. 

Physical ageing occurs also in crystalline polymers. It is sometimes, in crystalline polymers, difficult to distinguish physical ageing from effects due to recrystallization. It is, however, quite different physical ageing in crystalline polymers occurs even when the temperature history precludes recrystalliz-ation. In crystalline polymers, as in glassy polymers, it is due to a small... 

Still another related effect can be observed when a quenched glassy polymer is subjected to varying mechanical history by successive stress relaxation experiments in uniaxial extension. The relaxation times of poly(methyl methacrylate) appear to increasp with this progressive stress history more rapidly than with the lapse of... 

Given this practical importance, it is obviously awkward that the equilibrium constants of the dual mode sorption equations cannot be correlated with the properties of the polymer and of the permeant. Such correlations are reasonably successful in the rubbery state. Owing to.the effects of mechanical and thermal history of the glass on the incidence and effective surface area of the voids, a reliable generalized correlation for prior estimations of the three constants for gas sorption in glassy polymers may never be possible. 

Penetrant-Induced Effects. History-dependent properties of glassy polymers are well documented in terms of thermal (113,114) and mechanical U15) properties. Studies have related excess enthalpy changes measured by differential scanning calorimetry to changes in small-molecule sorption (116,117). Many studies have reported penetrant-induced history-dependent (or conditioning) effects for gas and vapor sorption and transport properties in glassy... 

Clarke and co-workers studied the effect of chain configurational properties on the stress—strain behavior of glassy linear polymers. They examined the relationship between chain structure and strain hardening by employing controlled stress molecular dynamics on a polyethylenelike chain. Variation of the sample preparation history produces chemically identical materials with vastly different responses to applied stress. 

Figure 3.1. Schematic illustration of temperature dependences of the specific volumes of amorphous materials. This figure also illustrates the effects of the nonequilibrium nature of glass structure, which results from kinetic factors. Glass 1 and Glass 2 are specimens of the same polymer, but subjected to different thermal histories. For example, Glass 1 may have been quenched from the melt very rapidly, while Glass 2 may either have been cooled slowly or subjected to volumetric relaxation via annealing ( physical aging ) in the glassy state.

In addition to the free volume [36,37] and coupling [43] models, the Gibbs-Adams-DiMarzo [39-42], (GAD), entropy model and the Tool-Narayanaswamy-Moynihan [44—47], (TNM), model are used to analyze the history and time-dependent phenomena displayed by glassy supercooled liquids. Havlicek, Ilavsky, and Hrouz have successfully applied the GAD model to fit the concentration dependence of the viscoelastic response of amorphous polymers and the normal depression of Tg by dilution [100]. They have also used the model to describe the compositional variation of the viscoelastic shift factors and Tg of random Copolymers [101]. With Vojta they have calculated the model molecular parameters for 15 different polymers [102]. They furthermore fitted the effect of pressure on kinetic processes with this thermodynamic model [103]. Scherer has also applied the GAD model to the kinetics of structural relaxation of glasses [104], The GAD model is based on the decrease of the crHiformational entropy of polymeric chains with a decrease in temperature. How or why it applies to nonpolymeric systems remains a question. 

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