Boyer-Spencer rule

So otiTg 0.2, which is very approximately the Boyer—Spencer rule. 

Ev/Ep can be calculated from segmental relaxation times for polymers and rotational correlation times of molecular liquids, measured over a range of thermodynamic conditions. Plots of the activation energy ratio versus y can be fit using a value oi apTg = 0.18 0.01 (Casalini and Roland, 2004b), consistent with the Boyer-Spencer rule. 

FIGURE 6.32 (Top) Product of the glass transition temperature and the thermal expansion coefficient of the rubber at Tg for 51 polymers. (Bottom) Product of Tg and the difference in thermal expansivity of the rubber and glassy states for the same materials. The data fall close to the respective predictions of the Boyer-Spencer and Simha-Boyer rules (Section (v)) (Krause et al., 1965). 

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