The reference point for liquid relaxation processes. II. Melt viscosity of polyisobutylene

Published (Fox and Flory) viscosity—temperature data for polyisobutylene are expressed by a modified Arrhenius equation: log η = log A + B ′/( T ‐ T 0 ). For higher molecular weight fractions ( M > 2000) with estimated glass temperatures in the range T g = −64 to −79°C., the derived reference temperature T 0 is −150 (±10)°C., and B ′ = 1240°. By comparison with Fox and Flory's empirical equations, the molecular weight dependency of the A parameter, below and above the “chain‐entanglement” point ( M = 17000), is derived. The modified Arrhenius equation can also be expressed with WLF (Williams‐Landel‐Ferry) constants, where T 0 = T g − C and B ′ = C C . The melt viscosity—temperature behavior is consistent with free−volume concepts if v f ⋍ ( T − T 0 ), as suggested by the Cohen‐Turnbull theory.