Soluble Hydrogen-bonding Interpolymer Complexes in Water: A Small-Angle Neutron Scattering Study

TL;DR

This study uses small-angle neutron scattering to investigate hydrogen-bonding interpolymer complexes between PAA and PDMAM side chains in water, revealing pH-dependent colloidal particle formation and their role in solution thickening.

Contribution

It provides detailed structural insights into PAA/PDMAM complexes in aqueous solution, highlighting pH effects and molecular weight influence, which were previously not well-characterized.

Findings

Complexation occurs at pH < 3.75, forming negatively charged colloids.

Estimated particle radius is around 165 Å.

Complexes involve more than five graft chains, acting as stickers.

Abstract

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.