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

On the basis of an isoviscosity criterion for the glass transition (η g ⋍ 10 13 poise) in liquids of low molecular weight, theoretical T g values were calculated for the n ‐alkane series by the equation log η = log A + B /( T − T 0 ), with the use of values reported by Lewis for the parameters. The T g / T 0 ratio reaches a limiting value of 1.25 and ϕ g = ( T g − T 0 )/2.3 B = 0.027, a constant. Extrapolation to (CH 2 ) ∞ gives T g = 200°K., T 0 = 160°K., and B = 640°K. This T g is consistent with other estimates for poly‐ethylene, and T 0 coincides with the temperature at which the “excess” liquid entropy for (CH 2 ) ∞ becomes zero from thermodynamic data. For polymer liquids it is proposed that E 0 = 2.3 RB is determined by the internal barriers to rotation for the “isolated” polymer chains. Thus, E 0 = 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.