A guided inquiry experiment for the physical chemistry laboratory has been developed in which students determine the Mark Houwink constants for poly(vinylpyrrolidone), or PVP, in water.  Student groups begin the laboratory by crafting a hypothesis for the dominant configuration of PVP in water: a tight coil, a random or looser coil, or a rigid rod.  Next, student groups plan a procedure to measure flow times of aqueous solutions of selected concentrations of four different molecular weights of PVP using an Ubbelohde dilution viscometer.  These flow times are then measured and subsequently used to calculate relative and specific viscosities.  From linear regression analysis of plots involving these viscosities versus concentration, student groups find the intrinsic viscosity.  During the laboratory session the following week, student groups obtain the molar mass of each PVP sample using matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI TOF MS).  Linear regression analysis of a plot of log [intrinsic viscosity] versus log [molecular weight] yields the Mark Houwink parameters �a� and �K�.  Student groups make comparisons between these two values and those found in the literature, in addition to determining the shape of PVP in water based on the �a� parameter.  For larger laboratory sections different student groups could be assigned different solvents for PVP.  Another possibility would be to assign different polymers with water as the solvent, particularly biopolymers if a number of biochemistry majors are enrolled in the course.  Nevertheless, the experiment that has been developed ultimately allows students to connect polymer and solvent molecular structure with polymer configuration in solution while also introducing the routine analytical technique of intrinsic viscosity with the emergent polymer characterization method of MALDI TOF MS.

Guided inquiry experiment for the determination of the configuration of a polymer in water

246th National Meeting (2013)

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