Direct chemical substitution

A vast array of polymer model hosts have been synthesized and studied. Side chain substituted PPV, PPP, PANI, PT and various copolymer derivatives have all appeared in the literature. From a structural standpoint, the most important defining characteristic is the presence of two chemically dissimilar building blocks; the non-polar flexible side chains and the stiff $\pi$-conjugated main chains. Given the opportunity, these polymers will adopt structures which produce a phase separation of the two fundamental units restricted by the chemical linkage which binds them together and any additional steric packing constraints. The net result is that solvent cast films or precipitated powders commonly form layered, semicrystalline structures whereby the alkyl side chains appear as spacers between nested stacks of the main chains[] as seen by the three differing structural motifs contained in Fig. 14.

 

Figure 14: Various possible lamellar structures appropriate for poly(3-alkylthiophenes) and other flexible side chain containing conducting polymer hosts. (a) Schematic model exhibiting no main chain or side chain tilts and no interlayer alkyl chain intermixing. (b) Schematic model exhibiting no main chain or side chain tilts and the maximum interlayer alkyl chain intermixing. (c) Schematic model exhibiting main chain (i.e., a non-zero setting angle) and side chain tilts with no interlayer alkyl chain intermixing.