Collapse of Flexible−Semiflexible Copolymers in Selective Solvents:  Single Chain Rods, Cages, and Networks

We examine the single chain behavior of block copolymers with flexible and semiflexible blocks. For these flexible−semiflexible copolymers two different solvent conditions are examined. In one case the solvent is poor for the semiflexible blocks and good for the flexible blocks, and in the other this situation is reversed. When the solvent is poor for the semiflexible blocks, we find a rodlike state at high stiffness and an isotropic globule at low stiffness. For the opposing case where the solvent is good for the semiflexible blocks we observed the formation of single molecule networks. In these networks the collapsed flexible blocks form nodes linked together by semiflexible blocks. Such a system is in principle similar to a multichain associating telechelic, except that the linkers in this case are not flexible and are joined into a single chain. The number of nodes in these networks was found to vary linearly with the number of segments in the copolymer. For polymers with a relatively small number of segments, open tetrahedral cages were observed while those with many more segments formed larger networks comprised of many such tetrahedra.