Edinburgh Napier University

  Aqueous solutions of amphiphilic polymers
usually comprise of inter- and intramolecular
associations of hydrophobic groups often leading to a
formation of a rheologically significant reversible
network at low concentrations that can be identified
using techniques such as static light scattering and
rheometry. However, in most studies published till
date comparing water soluble polymers with their
respective amphiphilic derivatives, it has been very
difficult to distinguish between the effects of molecular
mass versus hydrophobic associations on hydrodynamic
(intrinsic viscosity [g]) and thermodynamic
parameters (second virial coefficient A2), owing to the
differences between their degrees of polymerization.
This study focuses on the dilute and semi-dilute
solutions of hydroxyethyl cellulose (HEC) and its
amphiphilic derivatives (hmHEC) of the same molecular
mass, along with other samples having a different
molecular mass using capillary viscometry, rheometry
and static light scattering. The weight average molecular
masses (MW) and their distributions for the nonassociative
HEC were determined using size exclusion chromatography. Various empirical approaches developed
by past authors to determine [g] from dilute solution viscometry data have been discussed. hmHEC with a sufficiently high degree of hydrophobic modification was found to be forming a rheologically significant network in dilute solutions at very low concentrations as opposed to the hmHEC with a much lower degree of hydrophobic modification which also enveloped the hydrophobic groups inside the supramolecular cluster as shown by their [g] and A2.
The ratio A2MW/[g], which takes into account hydrodynamic as well as thermodynamic parameters, was
observed to be less for associative polymers compared
to that of the non-associative polymers.