Self-assembly in ω-functionalized block copolymers of styrene and isoprene

The spatial organization of end-functionalized diblock copolymers of styrene and isoprene revealed two separate levels of microphase separation: one between the two blocks forming the microdomain and another between the polar and non-polar material. The association produced by the latter process has a pronounced effect on the dynamics as revealed in rheology and dielectric spectroscopy. The introduction of a polar group into the different chain-ends has a dramatic effect on the phase behavior of the diblock copolymers and provides new ways of controlling their miscibility.     

Binary Polymer Mixtures in Selective Solvents: Interfacial Structure

Summary: The interaction of a large polymer droplet (formed by a poorly soluble polymer A) with a soluble polymer additive (polymer B) is investigated in the framework of a mean‐field approach. We found that polymer B may tend to adsorb on the surface of the droplet even when it is immiscible with polymer A in the droplet and is soluble in the solvent surrounding the droplet. We calculated the concentration profiles of both polymers A and B near the interface and established conditions for polymer B accumulation at the interface. The dependencies of the surface tension and the interfacial excess of polymer B on its bulk concentration are also calculated. We found that even a very small amount of homopolymer B additive may result in a significant reduction of the interfacial tension (by a factor of 2). The effect is stronger if the additive is more flexible than the insoluble polymer.

The region of parameters where B from dilute solution is adsorbed at the A/solvent interface (II).     

Intramolecular phase separation of a copolymer chain with mobile primary structure

The phenomenon of intramolecular phase separation of a single copolymer chain with mobile primary structure (i.e., a polymer chain with reversibly adsorbable ligands) in dilute solution is investigated on the basis of a Flory-type interpolation theory of the coil-globule phase transition. It is shown that under certain critical conditions the stability of the homogeneous primary structure is violated and intramolecular phase separation takes place. Phase diagrams for the cases of rigid and flexible chains are calculated. The main characteristics of a polymer chain in the two-phase state (such as fraction of monomeric units, swelling coefficient and fraction of units with ligands for coexisting intramolecular phases) are investigated.     

Computer simulation of globules with microstructure

We present recent data of our Monte Carlo computer simulation study of properties of AB-copolymer globules which depend strongly on the primary sequence of A and B monomeric units. Different primary sequences have been studied: random, random-block, regular and designed ones by using some particular spatial conformation of a homopolymer chain (we have compared here three models: proteinlike copolymers, AB-copolymers modeling membrane proteins and ABC-copolymers modeling proteins with active enzymatic center). We have found several evidences for the fact that an AB-copolymer chain with a primary sequence prepared on the basis of a particular conformation of a homopolymer chain by some “coloring” procedure preserves the “memory” about its “parent” spatial conformation. Analyzing the power spectra of AB-sequences, we find the existence of long-range power-law correlations for the copolymers with specially designed primary sequences.     

A three‐state model for counterions in a dilute solution of weakly charged polyelectrolytes

In this paper we consider the influence of counterion distribution on the behavior of polyelectrolyte systems. We propose the unified model to describe and to compare the swelling and collapse properties of single polyelectrolyte chains in dilute solutions, microgel particles of various molecular masses, and (as a limiting case) macroscopic gels. A novel feature of the new approach is that we distinguish three possible states of counterions: free counterions inside and outside the polymer macromolecule and a bound state of counterions forming ion pairs with corresponding ions of polymer chains. The latter possibility becomes progressively important when macromolecules or gels shrink. In this case the formation of a supercollapsed state is possible, when all couterions are trapped and form ion pairs. On the other hand, the fact that counterions can float in the outer solution affects essentially the conformation of polyelectrolyte chains in dilute solutions of good quality where practically all counter ions can escape the space inside polymer coils and the repulsion between uncompensated charges plays an important role in the chain behavior.