to remarkable advances in controlled radical polymerization techniques, such as
atom-transfer radical polymerization (ATRP), stable free-radical polymerization
(SFRP), and reversible addition-fragmentation transfer (RAFT) polymerization
[19, 20]. As a result, well-defined star-shaped polyelectrolytes and star-like
polyionic species (micelles of ionic amphiphilic block copolymers) as well as
cylindrical polyelectrolyte brushes can now be utilized as polymeric components
to be involved in interpolyelectrolyte complexation. This opens new possibilities
for design of a novel generation of IPECs having a distinct compartmentalized
structure. These problems and points will be considered in this review.
2 Formation and Basic Properties of Interpolyelectrolyte
Complexes
2.1 Peculiarities of IPEC Formation
During recent decades, considerable attention has been paid to interpolymer
interactions and interpolymer complexes. This interest is motivated by a number
of fundamental and application-oriented problems. In a fundamental aspect, interpolymer interactions are of significant importance because of the possibilities for
design and fabrication of novel polymeric co-assemblies, structures, and materials.
Such macromolecular co-assemblies (also referred to as interpolymer complexes)
possess unique properties that are remarkably different from the properties of
their polymeric components. In the simplest case, they result from “weak” mutual
attraction of chemically and/or stereo-complementary macromolecules. Thus,
“stereocomplexes” formed due to van der Waals interaction between stereoregular
poly(b-propiolactone)s are well known [21]. Interpolymer complexes might also be
stabilized via hydrogen bonds between monomer units of the polymeric counterparts
[22, 23], for example, co-assemblies of poly(carboxylic acid)s with polyethers,
i.e., poly[oxyethylene(propylene) glycol]s. Despite the low attraction energy between
complementary monomer units, such interpolymer complexes are rather stable
because of the cooperative character of interpolymer interaction. At the same time,
they can reversibly dissociate to their polymeric components if certain conditions
(temperature, pH, ionic strength, etc.) are met. This opens a unique opportunity for
design and fabrication of new polymeric materials and structures of various scales
and dimensions (ranging from nano- to macroscopic) with variable characteristics,
which are determined by environmental conditions. Such materials and structures are
referred to as functional, whereas the co-assemblies themselves are regarded as
“smart.” Similar principles for construction of complex polymeric structures are
widely exploited and exemplified in nature by production of the most important
biological architectures, such as double helices (i.e., DNA) and fibrillar proteins
(e.g., collagen). Thus, the modern physical chemistry of polymers follows fundamental principles, which are widely used in nature.
Among interpolymer complexes, IPECs, which result from the interaction between
oppositely charged polyelectrolytes, are of a special interest. Such macromolecular
176
D.V. Pergushov et al.
atom-transfer radical polymerization (ATRP), stable free-radical polymerization
(SFRP), and reversible addition-fragmentation transfer (RAFT) polymerization
[19, 20]. As a result, well-defined star-shaped polyelectrolytes and star-like
polyionic species (micelles of ionic amphiphilic block copolymers) as well as
cylindrical polyelectrolyte brushes can now be utilized as polymeric components
to be involved in interpolyelectrolyte complexation. This opens new possibilities
for design of a novel generation of IPECs having a distinct compartmentalized
structure. These problems and points will be considered in this review.
2 Formation and Basic Properties of Interpolyelectrolyte
Complexes
2.1 Peculiarities of IPEC Formation
During recent decades, considerable attention has been paid to interpolymer
interactions and interpolymer complexes. This interest is motivated by a number
of fundamental and application-oriented problems. In a fundamental aspect, interpolymer interactions are of significant importance because of the possibilities for
design and fabrication of novel polymeric co-assemblies, structures, and materials.
Such macromolecular co-assemblies (also referred to as interpolymer complexes)
possess unique properties that are remarkably different from the properties of
their polymeric components. In the simplest case, they result from “weak” mutual
attraction of chemically and/or stereo-complementary macromolecules. Thus,
“stereocomplexes” formed due to van der Waals interaction between stereoregular
poly(b-propiolactone)s are well known [21]. Interpolymer complexes might also be
stabilized via hydrogen bonds between monomer units of the polymeric counterparts
[22, 23], for example, co-assemblies of poly(carboxylic acid)s with polyethers,
i.e., poly[oxyethylene(propylene) glycol]s. Despite the low attraction energy between
complementary monomer units, such interpolymer complexes are rather stable
because of the cooperative character of interpolymer interaction. At the same time,
they can reversibly dissociate to their polymeric components if certain conditions
(temperature, pH, ionic strength, etc.) are met. This opens a unique opportunity for
design and fabrication of new polymeric materials and structures of various scales
and dimensions (ranging from nano- to macroscopic) with variable characteristics,
which are determined by environmental conditions. Such materials and structures are
referred to as functional, whereas the co-assemblies themselves are regarded as
“smart.” Similar principles for construction of complex polymeric structures are
widely exploited and exemplified in nature by production of the most important
biological architectures, such as double helices (i.e., DNA) and fibrillar proteins
(e.g., collagen). Thus, the modern physical chemistry of polymers follows fundamental principles, which are widely used in nature.
Among interpolymer complexes, IPECs, which result from the interaction between
oppositely charged polyelectrolytes, are of a special interest. Such macromolecular
176
D.V. Pergushov et al.