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Free volumes in polystyrene and polyisobutylene

1964; Inderscience Publishers; Volume: 2; Issue: 3 Linguagem: Inglês

10.1002/pol.1964.100020307

1542-6246

A. A. Miller,

Polymer crystallization and properties

Abstract The melt viscosities of polystyrene and polyisobutylene fractions are expressed by a modified Arrhenius (M.A.) temperature equation, η = A exp { B /( T − T 0 )}, and by a free volume equation, η = A exp 1/{ f }, in which f = v f / v , the free volume fraction. Thus, it is assumed that f , as defined, is a linear function of temperature, since f = ( T − T 0 )/ B . By this method, the derived “occupied” volume, v s = v − v f , has a temperature dependence which is determined by the temperature coefficients of f and v (i.e., 1/ B and α l ) and is not related to the experimental α g value for the glass. For polyisobutylene, the temperature coefficient of v s is positive, while for polystyrene it is slightly negative. Possible effects of liquid structure in determining the temperature behavior of v s are suggested. Calculated viscosities and free volume fractions at the glass point, T g , over a wide range of molecular weight, M , in both polymers lead to the conclusion that the glass transition is primarily an “iso‐viscosity” (η g ≃ 10 13 poise), rather than an “iso‐free volume”, state. However, in the two polymers, both conditions can exist simultaneously for similar values of M . Thus at equal M , f g = ( T g = T 0 / B ) is about the same for both polymers. For M ≃ 100,000, f g ≃ 0.031. These observations support the view that the glass transition is primarily a kinetic, rather than a thermodynamic, phenomenon. The estimated time dependence of T g is found to differ in the two polymers at equal M and to vary with M in each case.