Contributions of torsional braid analysis to T u

The accomplishments of Borden Award Winner John K. Gillham and his colleagues using Torsional Braid Analysis (TBA) and Differential Scanning Calorimetry (DSC) to investigate the T g and T > T g or T u regions of anionic and thermal poly styrenes (PS) are evaluated and related to work on PS and other polymers and to controversies surrounding TBA and the Tu transition. Arguments are presented to refute the contention that T u by TBA is an artifact produced by the braid and the contention that T u has a relaxational nature but no thermodynamic basis. Two distinct behavior patterns are found for T u vs log M̄ n plots: quasi‐static methods such as DSC on fused films show T u to level off above M c and approach an asymptotic value of ∼435K; dynamic methods involving melt flow show that T u increases without limit above M c because of entanglements. A compilation is presented of 25 investigations of T u on polybutadiene, poly(methyl methacrylate) (PMMA), PS, plasticized PS, and atactic polypropylene, involving twenty experimental techniques. The behavior of zero shear melt viscosity for PS is summarized. Gillham's work has not only led to clarification of many isolated papers in the literature but has also inspired various parallel experimental and literature studies on T u . We conclude that T u is a molecular level transition which, like T g , exhibits both kinetic (relaxational) and thermodynamic aspects. It is shown that heat capacity should be a more sensitive method than dilatometry for studying the T u transition.