Synthesis and ordering of two‐dimensional polymers

The work to be discussed in this lecture departs from the usual focus of polymer science on linear chains and explores the “bulk” synthesis and properties of polymer molecules that can be considered shape‐persistent molecular objects. Shapes that are particularly interesting are those not common in the conformational space of linear chains, for example, two‐dimensional polymers shaped as plates or discs and macromolecules shaped as cylinders or parallelepipeds. The lecture focuses on a molecular object which is a rigid and internally anisotropic two‐dimensional polymer with planar dimensions greater than its thickness. The shape‐granting skeleton of this two‐dimensional polymer is built by covalent bonds. We have so far developed three different strategies for their bulk synthesis, all involving systems in which reactive oligomers organize spontaneously into the necessary planar assemblies to form the object. In one strategy molecular recognition events such as homochiral interactions play a key role in the formation of the two‐dimensional flat polymers /1/. A different methodology relies on nanophase separation in rodcoil block molecules in which a rigid segment is covalently bonded to a flexible one sharing the same backbone. The third strategy involves the folding of oligomers into hairpin structures which self assemble into two‐dimensional liquids. In these two last strategies the layered rodcoils or hairpins react to form the covalent backbones necessary to grant shape to the object. A computer simulation relevant to the experimental system suggests that large two‐dimensional polymers can be formed by extremely short backbones. The lecture will also describe examples of unique properties in advanced materials that could emerge from these rigid two‐dimensional objects. These examples include. materials with self‐organized surfaces of high chemical definition and temporal stability, self assembling membranes, molecular reinforcement, and films with remarkably stable electrical or optical properties.