Microphase Separation within a Comb Copolymer with Attractive Side Chains: A Computer Simulation Study

Computer simulation modelling of a flexible comb copolymer with attractive interactions between the monomer units of the side chains is performed. The conditions for the coil-globule transition, induced by the increase of attractive interaction, ε, between side chain monomer units, are analysed for different values of the number of monomer units in the backbone, N, in the side chains, n, and between successive grafting points, m. It is shown that the coil-globule transition of such a copolymer corresponds to a first-order phase transition. The energy of attraction (ε) required for the realisation of the coil-globule transition decreases with increasing n and decreasing m. The coil-globule transition is accompanied by significant aggregation of side chain units. The resulting globule has a complex structure. In the case of a relatively short backbone (small value of N), the globule consists of a spherical core formed by side chains and an enveloping shell formed by the monomer units of the backbone. In the case of long copolymers (large value of N), the side chains form several spherical micelles while the backbone is wrapped on the surfaces of these micelles and between them.

Self-Organization in Solutions of Stiff-Chain Amphiphilic Macromolecules

Conformational properties of amphiphilic stiff-chain macromolecules in concentrated solutions in poor solvent have been studied via computer modeling. We have found that the conformational state of macromolecules in such systems depends on the macromolecular stiffness and on the way the solution has been prepared. Thus, if the concentration of globules increased from a very diluted solution, the globules remain stable, independent of the macromolecular stiffness, and do not aggregate even in concentrated solutions. On the other hand, if the solvent quality is gradually decreased in a solution with a concentration much larger than that of a semidilute solution, then relatively flexible chains form separate globules, whereas semirigid macromolecules tend to aggregate and form braid-like conformations. The results obtained agree with the published experimental data and can be used for directed synthesis of macromolecules modeling the behavior of biopolymers.

Conformational Properties of Rigid-Chain Amphiphilic Macromolecules: The Phase Diagram

The coil–globule transition in rigid-chain amphiphilic macromolecules was studied by means of computer simulation, and the phase diagrams for such molecules in the solvent quality–persistence length coordinates were constructed. It was shown that the type of phase diagram depends to a substantial extent on the degree of polymerization of a macromolecule. Relatively short amphiphilic macromolecules in the poor-solvent region always form a spherical globule, with the transition to this globule involving one or two intermediate conformations. These are the disk globule if the Kuhn segment is relatively large and the string of spherical micelles or the disk globule in the case of relative flexible chains. The phase diagram of a long rodlike amphiphilic chain turned out to be even more complex. Namely, three characteristic regions were distinguished in the region of a poor solvent, depending on the chain rigidity: the region of a cylindrical globule without certain order in the main chain, the region of the cylindrical globule with blobs having the collagen ordering of the chain, and the region of coexistence of collagen-like and toroidal globules. In the intermediate transitional region, not only conformations of strings of spherical micelle beads but also the necklace conformations in which the polymer chain in each bead has collagen ordering can occur in this case.