  The hydrogen-bonding interpolymer complexation between poly(acrylic acid)
(PAA) and the poly(N,N-dimethylacrylamide) (PDMAM) side chains of the
negatively charged graft copolymer poly(acrylic
acid-co-2-acrylamido-2-methyl-1-propane sulfonic acid)-graft-poly(N, N
dimethylacrylamide) (P(AA-co-AMPSA)-g-PDMAM), containing 48 wt % of PDMAM, and
shortly designated as G48, has been studied by small-angle neutron scattering
in aqueous solution. Complexation occurs at low pH (pH < 3.75), resulting in
the formation of negatively charged colloidal particles, consisting of
PAA/PDMAM hydrogen-bonding interpolymer complexes, whose radius is estimated to
be around 165 A. As these particles involve more than five graft copolymer
chains, they act as stickers between the anionic chains of the graft copolymer
backbone. This can explain the characteristic thickening observed in past
rheological measurements with these mixtures in the semidilute solution, with
decreasing pH. We have also examined the influence of pH and PAA molecular
weight on the formation of these nanoparticles.
