Page 124 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Molecular Weight of Polymers 87

larger entropy values when solubility is achieved in comparison to polymers. Polymers also take
longer to dissolve since it takes time for the solvent molecules to penetrate the polymer matrix.
8. Flory and Huggins developed an interaction parameter that may be used as a measure of the
solvent power of solvents for amorphous polymers. Flory and Krigbaum introduced the idea of
a theta temperature, which is the temperature at which an infinitely long polymer chain exists as

a statistical coil in a solvent.
9. Hildebrand developed solubility parameters to predict the solubility of nonpolar polymers
in nonpolar solvents. The solubility parameter is the square root of the CED. For polar sol-
vents, special solvent-polymer interactions can be incorporated into the solubility parameter
approach.

GLOSSARY
Affinity chromatography: Chromatography in which the resin is designed to contain moieties

that interact with particular molecules and/or units within a polymer chain.
Bingham plastic: Plastic that does not fl ow until the external stress exceeds a critical thresh-
old value.
Brownian motion: Movement of larger molecules in a liquid that results from a bombardment
of smaller molecules.
Buoyancy factor: In ultracentrifugation experiments, it determines the direction of polymer
transport under the effect of centrifugal forces in the cell.
Chromatography: Family of separation techniques based on the use of a medium that shows
selective absorption.
Colligative properties: Properties of a solution that are dependent on the number of solute
molecules present.
Cloud point: Temperature at which a polymer starts to precipitate when the temperature is
lowered.
Cohesive energy density (CED): Heat of vaporization per unit volume.
Commercial polymer range: Molecular weight range high enough to have good physical prop-
erties but not too high for economical processing.
Cryometry: Measurement of number-average molecular weight from freezing point
depression.
Ebulliometry: Measurement of number-average molecular weight from boiling-point
elevation.
Effective hydrodynamic volume: Cube of the root-mean-square end-to-end distance of a poly-
mer chain.
Electrophoresis: Form of chromatography that uses an electric field to separate molecules.

End group analysis: Determination of number-average molecular weight by determination of
end groups.
Flory–Huggins theory: Theory used to predict the equilibrium behavior between liquid phases
containing polymer.
Fractional precipitation: Fractionation of polydisperse systems by addition of small amounts
of nonsolvent to a solution of polymer.
Fractionation of polymers: Separation of a polydisperse polymer into fractions of similar
molecular weight.
Gel permeation chromatography: Type of liquid–solid elution chromatography, which sepa-
rates solutions of polydisperse polymer solutions into fractions containing more homoge-
neous chain sizes by means of a sieving action of a swollen cross-linked polymeric gel.
Also called SEC.

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