Journal of Applied Physics · 1950 · 2.4K citations · 14 references
Natural SciencesChemistryMaterials SciencePhysical ChemistryPolymer ChemistryRheologyPolymer Chain ConformationPolymer CharacterizationPolymer Physical ChemistryPolymer PhysicsPolymer RheologyPolymer StructureLocal StructureMolecular Weight DependenceMolecular Weight Dependence Of Polymer PropertiesPolymer Conformation In MeltsPolymer Molecular CharacteristicsPolystyreneViscosity-temperature BehaviorViscosity-temperature Effects
The authors aim to interpret and correlate observations by hypothesizing that end groups disturb local configurational order proportionally to their number. They analyze dilatometric and viscometric data of fractionated polystyrenes with diethylbenzene end groups, linking end‑group effects to local configurational order. The data reveal that second‑order transition temperature, viscosity‑temperature coefficient, and specific volume change rapidly with molecular weight, reaching asymptotic limits near M≈30 000, and empirical expressions relate these properties to molecular weight and temperature; the second‑order transition is not isoviscous, and the local configurational structure is temperature‑independent below the transition.
Dilatometric and viscometric data on fractionated polystyrenes containing diethylbenzene end groups are presented over wide temperature ranges. The second-order transition temperature, viscosity-temperature coefficient, and specific volume all change rapidly with increasing molecular weight toward asymptotic limits which are practically reached at M≅30,000. Empirical expressions are presented relating these properties to molecular weight and temperature. In each case the dependence on molecular weight is expressed as a simple function of M̄n−1. These observations are interpreted and correlated on the basis of the hypothesis that the local configurational order in a liquid polymer is disturbed by the introduction of end groups to a degree that is proportional to their number. The second-order transition does not represent an isoviscous state. The internal local configurational structure appears to be equivalent, and independent of temperature, in all polystyrenes below their second-order transition temperatures.
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Norman Bekkedahl · Journal of research of the National Bureau of Standards · 1949 · 144 citations · Full text