Breakdown of time-temperature superposition principle and universality of chain dynamics in polymers

Detailed comparison of temperature dependences of segmental (tau(alpha)) and chain (tau(n)) relaxation times shows that decoupling of these relaxation processes occurs (the ratio tau(n)/tau(alpha) starts to drop) at a similar range of tau(alpha) similar to 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 tau(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.