  The formation of soluble hydrogen-bonding interpolymer complexes between
poly(acrylic acid) (PAA) and poly(acrylic
acid-co-2-acrylamido-2-methyl-1-propane sulfonic acid)-graft-poly(N, N
dimethylacrylamide) (P(AA-co-AMPSA)-g-PDMAM) at pH = 2.0 was studied. A
viscometric study showed that in semidilute solution a physical gel is formed,
due to the interconnection of the anionic P(AA-co-AMPSA) backbone of the graft
copolymer, in a transient network, by means of the complexes formed between the
PDMAM side chains of the graft copolymer and PAA. Dynamic and static light
scattering measurements, in conjunction with small angle neutron scattering
measurements, suggest the formation of core-shell colloidal nanoparticles in
dilute solution, comprised by an insoluble PAA/PDMAM core surrounded by an
anionic P(AA-co-AMPSA) corona. Even if larger clusters are formed in semidilute
solution, the size of the insoluble core remains practically stable. Atomic
force microscopy performed under ambient conditions, reveal that the particles
collapse and flatten upon deposition on a substrate, with dimensions close to
the ones of the dry hydrophobic core.
