Calorimetric Analysis Of Macromolecules Lab Report
INTRODUCTION In this lab, we will be measuring the viscosity of samples of polyvinyl alcohols in order to determine the molecular mass of their components. Polyvinyl alcohol is an example of a synthetic polymer, which is a macromolecule. The general chemical structure of such compounds are well-characterized, although variation in characteristics such as molar mass, chain length, and extent of branching are not obvious from merely looking at their molecular formula. There is also the complication that macromolecules often have variations in chain length or molar mass even within a given sample. The idealized formula of polyvinyl alcohol is -(C2H2—CHOH)-n, which assumes consistent orientation in the addition of the vinyl acetate monomers1.
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50 mL of stock polymer solution will be pipetted into a 100 mL volumetric flask and filled to mark with distilled water. After mixing, the flask will be placed in the bath to equilibrate. To cleave the polymer, 0.25 g of solid KIO4 will be placed in a 250 mL flask along with 50 mL of polymer solution and up to 25 mL of water. After warming to 70ºC and stirring until completely dissolved, the flask will be transferred to the bath and stirred until cooled to 25ºC. To obtain a second concentration of both the cleaved and uncleaved polymer, 50 mL of each initial solution will be pipetted into a 100 ml flask and diluted to mark with water. After equilibration, the viscosity of both solutions of each polymer, and water (for reference) will be measured. The flow time for the pure water will be used to determine the apparatus constant B, (which is found by setting equal the viscosity of water over its density to this value, multiplied by the amount of time it takes for the upper meniscus to fall from the upper to lower fiducial mark in the measurement). For each sample, the viscosity and concentration per grams of polymer per 100 mL solution will be calculated, so that ηsp/c and (1/c)(ln η/η0) may be plotted against the c and extrapolated linearly to c=0 to find the [η] for the original and degraded polymer. The M ̅v and M ̅n will be calculated for both the original and degraded polymer, with which we can use to find a value for ∆. With this, we may identify the relationship between the ∆ and the rate constants kα and
50 mL of stock polymer solution will be pipetted into a 100 mL volumetric flask and filled to mark with distilled water. After mixing, the flask will be placed in the bath to equilibrate. To cleave the polymer, 0.25 g of solid KIO4 will be placed in a 250 mL flask along with 50 mL of polymer solution and up to 25 mL of water. After warming to 70ºC and stirring until completely dissolved, the flask will be transferred to the bath and stirred until cooled to 25ºC. To obtain a second concentration of both the cleaved and uncleaved polymer, 50 mL of each initial solution will be pipetted into a 100 ml flask and diluted to mark with water. After equilibration, the viscosity of both solutions of each polymer, and water (for reference) will be measured. The flow time for the pure water will be used to determine the apparatus constant B, (which is found by setting equal the viscosity of water over its density to this value, multiplied by the amount of time it takes for the upper meniscus to fall from the upper to lower fiducial mark in the measurement). For each sample, the viscosity and concentration per grams of polymer per 100 mL solution will be calculated, so that ηsp/c and (1/c)(ln η/η0) may be plotted against the c and extrapolated linearly to c=0 to find the [η] for the original and degraded polymer. The M ̅v and M ̅n will be calculated for both the original and degraded polymer, with which we can use to find a value for ∆. With this, we may identify the relationship between the ∆ and the rate constants kα and