The glass transition in amorphous polymers

The cohesive forces holding its different components together. The relevant components for the glass transition in amorphous polymers are chain segments. The cohesive forces can be quantified in terms of the cohesive energy density or the solubility parameter. 

It has been repeatedly emphasized throughout this book that the glass transition in amorphous polymers is accompanied by profound changes in their viscoelastic response. Thus the stress relaxation modulus commonly decreases... 

Factors affecting the glass transition in amorphous polymers... 

FACTORS AFFECTING THE GLASS TRANSITION IN AMORPHOUS POLYMERS 195... 

Equation 21, sometimes called the WLF equation, was introduced as an empirical expression for a general curve flr(T) in which many different polymers had been reduced to standard states in a manner which will be described below. Its utility has been illustrated in the preceding section its physical significance will now be examined. First, a digression is necessary to consider the nature of the glass transition in amorphous polymers and supercooled liquids. 

Factors Affecting the Glass Transition in Amorphous Polymers... 

Two distinct models have been used for interpreting the influence of features such as chemical stmcture, molecular mass, cross-linking and plasticisers on the glass transition in amorphous polymers. The first approach considers changes in moleeular flexibility, which modify the ease with which conformational changes can take place. The alternative approach relates all these effects to the amount of free volume, which is assumed to attain a critical value at the glass transition. 

Figure 10.20 Schematic representation of the glass transition in amorphous polymers. The decrease in volume and enthalpy at 7, is referred to as physical ageing.

Lipatov, Y. S. The Iso-Free-Volume State and Glass Transition in Amorphous Polymers New Development of the Theory. Vol. 26, pp. 63 —104. 

Kanaya, T. and Kaji, K. Dynamcis in the Glassy State and Near the Glass Transition of Amorphous Polymers as Studied by Neutron Scattering. Vol. 154, pp. 87-141. 

Simha and Boyer22 applied the free-volume concept to describe glass transitions in amorphous polymers. By analogy with Eq. (12), it was assumed that the fractional free-volume/g at glass-transition temperature Tg is... 

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