Issue 5, 2007

Measuring the size of polymers with negative radii using MALS/QELS: an exploration of the thermodynamic radius

Abstract

The concept of ‘size’ in polymer science can have several interpretations, including definitions that rely on either statistical or equivalent-hard-sphere measures of the spatial extent of macromolecules in solution. A definition such as that of the equivalent thermodynamic radius (RT), which relies on the second virial coefficient of the polymer solution, offers the possibility of a zero or even a negative size parameter for macromolecules, depending on whether the polymer solution is in a theta or poor thermodynamic state, respectively. Here, we present the results of multi-angle light scattering measurements of RT for polystyrene and poly(methyl methacrylate), showing positive, negative, and zero values for this radius, depending on dilute solution thermodynamics. These results are augmented with measurements of the hydrodynamic radius, using quasi-elastic light scattering, and with random-walk-based calculations of the root-mean-square and viscometric radii. Re-examination of the literature provides additional examples of negative radii of polymers and oligomers.

Graphical abstract: Measuring the size of polymers with negative radii using MALS/QELS: an exploration of the thermodynamic radius

Article information

Article type
Paper
Submitted
13 Dec 2006
Accepted
07 Mar 2007
First published
21 Mar 2007

Analyst, 2007,132, 455-460

Measuring the size of polymers with negative radii using MALS/QELS: an exploration of the thermodynamic radius

M. J. Smith, I. A. Haidar and A. M. Striegel, Analyst, 2007, 132, 455 DOI: 10.1039/B618177E

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