Dilute Solutions of Block Copolymers. 2. Triblock Copolymers

Abstract

Dilute solutions of symmetric triblock copolymers ABA and BAB in a selective solvent, i.e., a solvent good for one type of monomers (A) and poor for the other (B), and of their constituent homopolymers were investigated by exact enumeration of pair configurations of cubic lattice chains generated by a Monte Carlo method. Quantities characterizing the size and the molecular shape were investigated as a function of the intermolecular distance between the chains. In addition, integral quantities of chain properties (related to concentration dependencies) were computed. On the whole, behavior of triblock copolymers was closer to that of athermal chains than to that of ϑ-homopolymers. Their architecture, however, significantly influenced the details. The pair distribution function of BAB exceeded unity at large distances as is characteristic for homopolymers in ϑ-solvents and poor solvents. Furthermore, behavior characteristic of ϑ-systems persisted for all distance dependent quantities investigated for BAB at large separations. This was not however sufficiently pronounced as to be reflected in the sign of integral quantities which again resembled those of the athermal system.

Monte Carlo simulation studies of the size and shape of linear and star-branched polymers embedded in the tetrahedral lattice

“…For instance, a virial expansion is necessary for the description of the osmotic pressure and the (average) size of the molecules is dependent on concentration. In highly diluted solutions, these effects of a non ideal behaviour may be attributed to interactions between two molecules (unaffected by the presence of other molecules) and the properties of the limiting case of a highly diluted solution of macromolecules may be evaluated by studying isolated pairs of molecules [17][18][19][20][21][22][23][24][25][26][27][28] . On the other hand, for the simulation of concentrated polymer solutions and polymer melts resort to many particle systems 16,29,30) is necessary.…”

Pair distribution function and related properties of star-branched chains

“…[27] By use of Eq. (4) the limiting slopes of concentration dependence were also evaluated for several types of diblock [29] and triblock [30] copolymers. Recently, the general validity of this procedure could be shown by comparison with the results obtained by direct simulation of multichain systems.…”

Concentration Dependence of Size, Shape, and Orientation of Copolymers, 1 – Linear Diblock and 4‐arm Hetero Star Polymers

“…In this way we investigated diblock (XY) and triblock (XYX) copolymers in common good, common theta as well as in selective solvents—the lengths of blocks being in the ratio 1:1 and 1:2:1, respectively—and compared their properties to those of their constituent homopolymers. Concentration was varied from the limiting case of an infinitely dilute solution (performed on isolated chains as intermolecular interactions between dissolved molecules may be disregarded in this restricted case)23–25 over slightly more concentrated but nevertheless highly diluted solutions (taking into account pairwise interactions between dissolved chains)26, 27 up to a polymer fraction of 0.8 (performing simulations of multi‐chain systems) 28–30. Among other things it turned out that dimensions of block copolymers in selective solvents are intermediate between those of their constituent homopolymers with dimensions of diblock copolymers being intermediate between those of the triblocks, the latter in turn being more expanded if the athermal block is in the middle of the chain than at the ends.…”