Interpolyelectrolyte Complexes Based on Polyionic Species of Branched Topology - Self Organized Nanostructures of Amphiphilic Block Copolymers - page 137

the complex coacervate core, whereas the others remain extended and form the
hydrated corona of the co-assemblies. Experimental observation that the hydrody-
namic radius of the formed co-assemblies only weakly depends on their base-molar
stoichiometry (degree of charge compensation of the branched HPE by GPE chains)
supports this first scenario. An alternative possibility (structure II) assumes that all
of the branches of the star-shaped HPE contribute segments of equal length to the
central core (complex coacervate) domain. The lyophilizing corona is formed by the
terminal segments of the star-shaped HPE that are not involved in the complexation
with chains of the linear GPE. Obtaining experimental proof of the thermodynam-
ically preferred structure of such macromolecular co-assemblies is a challenging
task; a deeper insight into this problem has been enabled by MD simulations and
scaling arguments, as discussed in Sect. 2.2.
An interesting example of macromolecular co-assemblies derived from star-
shaped polyionic species was reported by Ge et al. [ 81 ] . The authors found
that

a star-shaped double hydrophilic poly(methacrylic acid)-poly(ethylene

oxide) ) X , with PDVB being

poly(divinylbenzene) and X denoting the number of PMAA and PEO arms] can
interact in alkaline media with a double hydrophilic poly(ethylene oxide)- block -
quaternized

heteroarm copolymer [ ( PMAA ) X -PDVB- ( PEO

poly[2-(dimethylamino)ethyl methacrylate] (PEO- b -PDMAEMAQ)

diblock copolymer. At Z 1, well-defined water-

soluble onion-like (core-shell-corona) macromolecular co-assemblies are formed,
with a hydrophobic core consisting of a PDVB microgel. The interaction of the
PMA − arms of the hybrid coronas of such copolymer stars with the PDMAEMAQ +
blocks of the diblock copolymer generates an insoluble inner layer (shell) around
a PDVB core. Meanwhile, PEO blocks from both PEO- b -PDMAEMAQ and
(

=[ PDMAEMAQ ] / [ PMAA ]=

) X build up a hydrophilic nonionic corona that stabilizes
the whole complex in aqueous media.

PMAA ) X -PDVB- ( PEO

2.2 Molecular Dynamics Simulations

A pioneering attempt to unravel the internal structural organization of IPECs formed
from the interaction between oppositely charged star-shaped PEs (HPEs) and lin-
ear PEs (GPEs) was recently made by Larin et al. [ 89 ]. The total number of ionic
groups of a single PE star was taken to considerably exceed the total number of
ionic groups of a chain of an oppositely charged linear PE. Using MD simulations
(coarse-grained bead-rod model), the authors showed the stable inhomogeneous
structure of the formed macromolecular co-assemblies. Specifically, they demon-
strated that the resulting IPEC species comprise three distinct domains: (a) a dense
central domain where chains of the linear PE partially compensate the local charge
of the arms of the star-shaped PE; (b) a complex coacervate domain where the local
charge of the arms of the star-shaped PE is nearly fully compensated by chains of the
linear PE, the majority of which are found here; and (c) a periphery domain where
the charge of the arms of the star-shaped PE is considerably undercompensated.