Breakdown of Time−Temperature Superposition Principle and Universality of Chain Dynamics in Polymers

Detailed comparison of temperature dependences of segmental (τ α ) and chain (τ n ) relaxation times shows that decoupling of these relaxation processes occurs (the ratio τ n /τ α starts to drop) at a similar range of τ α ∼ 10 -5 −10 -7 s regardless of a polymer and its molecular weight. The degree of decoupling depends on polymer and is stronger in more fragile systems. The most intriguing result is a rather universal temperature dependence of τ n observed for the analyzed polymers when it is plotted vs T g / T . These observations call for a revision of current models describing the microscopic friction coefficient in polymer melts.