ISSN:
0098-1273
Schlagwort(e):
Physics
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
A formal definition of TLL as a function of M̄n for polystyrene was prepared with literature TLL values from torsional braid analysis (TBA), differential scanning calorimetry (DSC), and zero-shear melt viscosity η0. Data from six authors using anionically prepared PS and blends thereof were involved. The resultant linear least-squares regression line, TLL(°C) = 148.5 - 11.487 × 104M̄n-1 [standard error in TLL (calculated) 4.056 K, correlation coefficient R2 = 0.9534] is considered valid from M̄n = 2000 to the entanglement molecular weight Mc = 35,000. The “best” TLL values reported by Orbon and Plazek from double Arrhenius plots are well below this line for M̄v = 47,000, 16,400, 3400, and above it for M̄v = 1100. These best TLL values are artifacts arising from no or insufficient data points above or below TLL and/or too many data points near Tg. The associated high enthalpies of activation which they report confirm this diagnosis. The fact that these artificial TLL values tend to disappear when checked by the three-parameter Vogel equation, logη = logA + B exp[(T - T∞)-1], has no relevance to the controversy concerning the existence and meaning of TLL. The claim by Orbon and Plazek that TLL values obtained by TBA, DSC, and melt viscosity are all artifacts of the individual methods by which they were obtained is inconsistent with the excellent master plot which they generate. Alternative plotting devices which reveal TLL 〉 Tg from η0 vs. T-1 data, as developed by van Krevelen and Hoftyzer and by Utracki and Simha (not previously considered by either party), are reviewed. A statistical examination of the nature of the Vogel-Fulcher-Tammann-Hesse equation, based on synthetic data, is presented. Evidence for TLL in atactic polypropylene is offered based on published data by Plazek and Plazek. TLL is considered to possess both relaxational and quasiequilibrium attributes, just as Tg does.
Zusätzliches Material:
11 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pol.1985.180230103
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