Determination of Polymer Molecular Dimensions from Viscosity

1 Determination of Polymer Molecular Dimensions from Viscosity 

If is considered to be a universal constant, the average dimensions of polymer molecules in solution can be drived simply from their intrinsic viscosities and molecular weights. More specifically, the natural, or unperturbed, dimensions of the polymer chain can be estimated from the knowledge of intrinsic viscosity in a theta solvent (Kurata and Stockmayer, 1963 Stockmayer and Fixman, 1963). 

Problem 3.26 The intrinsic viscosity of polystyrene of molecular weight 3.2x10 in toluene at 30°C was determined to be 0.846 dL/g. In a theta solvent (cyclohexane at 34°C) the same polymer had an intrinsic viscosity of 0.464 dL/g. Calculate (a) unperturbed end-to-end distance of the polymer molecule, (b) end-to-end distance of the polymer in toluene solution at 30°C, and (c) volume expansion factor in toluene solution. ( = 2.5x10 mol ) 

Problem 3.27 For a fractionated sample of cis-l,4-polybutadiene of molecular weight 1.23x10° intrinsic viscosities were measured (Moraglio, 1965) in three different solvents at respective theta temperatures. From the results given below detennine the variation of the unperturbed dimensions of the polymer molecule with temperature. 

Note The parameter iln(r )o/ i7 appears in the theoretical treatments of thermoelasticity of macromolecular substances. 

Average linear expansion factor, a = (ff ) = 1.28 Volume expansion factor, = (1.28) = 2.1 

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