The intrinsic viscosity of a polymer solute in a solvent, [h]solvent, is the portion of

Chapter 12, Problem 12.147

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The intrinsic viscosity of a polymer solute in a solvent, [h]solvent, is the portion of the total viscosity due to the solute and is related to solute shape. It has also been found to relate to intermolecular interactions between solvent and polymer: higher [h]solvent means stronger interaction. The [h]solvent values of polymers in solution are given by the Mark-Houwink equation, [h]solvent 5 K}a, where } is the molar mass of the polymer and K and a are constants specific to the polymer and solvent. Use the data below for substances at 258C to answer the following questions: (a) A polystyrene sample has a molar mass of 104,160 g/mol. Calculate the intrinsic viscosity in benzene and in cyclohexane. Which solvent has stronger interactions with the polymer? (b) A different polystyrene sample has a molar mass of 52,000 g/mol. Calculate its [h]benzene. Given a polymer standard of known }, how could you use its measured [h] in a given solvent to determine the molar mass of any sample of that polymer? (c) Compare [h] of a polyisobutylene sample [repeat unit (CH3)2CCH2] with a molar mass of 104,160 g/mol with that of the polystyrene in part (a). What does this suggest about the solventpolymer interactions of the two samples?