Kinetic interpretation of the glass transition: Glass temperatures of n‐alkane liquids and polyethylene

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Abstract
On the basis of an isoviscosity criterion for the glass transition (ηg ⋍ 1013 poise) in liquids of low molecular weight, theoretical Tg values were calculated for the n‐alkane series by the equation log η = log A + B/(T − T0), with the use of values reported by Lewis for the parameters. The Tg/T0 ratio reaches a limiting value of 1.25 and ϕg = (Tg − T0)/2.3B = 0.027, a constant. Extrapolation to (CH2)∞ gives Tg = 200°K., T0 = 160°K., and B = 640°K. This Tg is consistent with other estimates for poly‐ethylene, and T0 coincides with the temperature at which the “excess” liquid entropy for (CH2)∞ becomes zero from thermodynamic data. For polymer liquids it is proposed that E0 = 2.3RB is determined by the internal barriers to rotation for the “isolated” polymer chains. Thus, E0 = 2.9 kcal./mole for polyethylene, 3.0 kcal./mole for polystyrene, 5.7 kcal./mole for polyisobutylene, and 1.9 kcal./mole for polydimethylsiloxane.