Segmental melting hypothesis

EKNET was first announced by Ibar in his 1975 doctoral thesis and only recently related experimentally to Tp, Tg, and T// events. It needs to be tested against all aspects of Tn phenomena in order to compare it with the "segmental melting" hypothesis. 

This hypothesis postulates that Tp occurs when the segments "melt," liberating a AH of "melting" as the chain gains entropy, AS, from its enhanced freedom. Segmental melting is not sharp and hence the Tp process is diffuse. This hypothesis is consistent with many of the known facts about Tp as recited in ref 1 and Section I of this manuscript ... 

This equation was derived from die hypothesis that small molecules move by jumping into unoccupied sites or holes. For many small molecule liquids , = 10—30 kJ/mol. Polymer melts also obey this equation at temperatures well above their glass transition, l th polymers, viscosity may be governed by successive jumps of segments of the chain. , ranges from about 2S kJ/mol for polyethylene to 60 for polystyrene and 85 for polycarbonate and polyvinyl chloride. 

The basic hypothesis is that along any polymer chain there is a Maxwellian distribution of energies with several low energy "cold spots." Inter- and intra-association of cold spots gives rise to a structure which he assumed disappeared at a temperature which increased linearly with log molecular weight, much as Tyin Fig. 5. Ueberreiter s model for structure is inherently similar to that of Frenkel depicted by us in Fig. 9 of ref. 1, as segment-segment association which melts out at T//(see Fig. 11). 

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