The intrinsic viscosity of a solute in a solvent,

Chapter 12, Problem 12.143

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The intrinsic viscosity of a solute in a solvent, [?]solvent, is the portion of the total viscosity due to the solute and is related to solute shape. In polymer science, it relates as well to intermolecular interactions between solvent and polymer: higher [?]solvent means stronger interaction. The [?]solvent values of polymers in solution are given by the Mark-Houwink equation, [?]solvent? 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 25C to answer the following questions: A C B Polystyrene Polyisobutylene 9.5?10?3 8.1?10?2 8.3?10?2 2.6?10?1 Benzene Cyclohexane Benzene Cyclohexane 0.74 0.50 0.50 0.70 Polymer Solvent K (mL/g) a (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 [?]benzene. Given a polymer standard of known , how could you use its measured [?] in a given solvent to determine the molar mass of any sample of that polymer? (c) Compare [?] 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 solvent-polymer interactions of the two samples? 1