Interpolyelectrolyte Complexes Based on Polyionic Species of Branched Topology - Self Organized Nanostructures of Amphiphilic Block Copolymers - page 133

This review deals with recently obtained experimental results on IPECs based on
branched PE species, specifically including PE stars, star-like micelles generated in
aqueous solutions of ionic amphiphilic block co- and terpolymers, and cylindrical
PE brushes. In addition, we will also present the results of molecular dynamics
(MD) simulations performed for some of these systems, which enable the possible
structural organization of the formed macromolecular co-assemblies to be revealed.

2 IPECs Based on Polyelectrolyte Stars

2.1 Experimental Results

The advances in controlled polymerization achieved in recent years have opened
up the possibility of synthesizing well-defined star-shaped PEs, particularly those
containing a large number of arms. To the best of our knowledge, no publications on
the interaction of PE stars with oppositely charged macromolecules or investigations
on the properties of the resulting macromolecular co-assemblies can be found in the
literature to date, except for a few papers [ 79 - 81 ] that are discussed below.
Pergushov et al. [ 79 ] demonstrated for the first time that the interaction of
poly(acrylic acid) stars [ ) X ,where X denotes the number of arms] with rel-

atively long cationic PEs, namely quaternized poly(4-vinylpyridine) (P4VPQ), at
pH 7 can lead to the formation of water-soluble IPECs in which the star-shaped PEs
play a lyophilizing role, i.e., they act as HPEs, providing solubility of the whole
macromolecular co-assemblies in aqueous media. Specifically, it was observed that
the addition of P4VPQ into an aqueous solution of the

( PA A

) X stars causes macro-
scopic phase separation of the mixture of oppositely charged polymeric components
only if their base-molar ratio Z

( PA A

N + ] / [ COO − + exceeds a

certain threshold value Z M (Fig. 2 ) , thereby strongly suggesting the formation of
water-soluble IPECs at Z

( Z =[ COOH ] , Z < 1 )

Z M . The values of Z M were found to increase with an
increase in the number of arms (Fig. 2 , inset). This tendency, as shown by the same
authors [ 79 ], became more pronounced at higher ionic strengths of the aqueous mix-
tures of oppositely charged polymeric components.
It is remarkable that an aqueous solution of the reference linear PAA becomes
turbid after adding the first portion of the aqueous solution of P4VPQ (Fig. 2 , inset).
This clearly indicates that the reference linear PAA, in contrast to the

<

) X stars,
cannot form water-soluble IPECs via this method under the same conditions and
also clearly manifests a pronounced effect of the topology of the polymeric com-
ponent involved in interpolyelectrolyte complexation on the possibility of preparing
water-soluble macromolecular co-assemblies.
A detailed examination of the homogeneous mixtures of

( PA A

) X stars and
P4VPQ [ 79 ] by dynamic light scattering (DLS) provided evidence of a distinct co-
existence of the two populations of macromolecular co-assemblies: (1) A dominant
fraction comprising particles of water-soluble IPECs that result from interactions
between oppositely charged polymeric components; their hydrodynamic size was

( PA A