Interaction of side-chains in poly(3-alkylthiophene) lattices

Atomistic simulation investigations of poly(3-alkylthiophene) lattices lead to fully relaxed structures that are consistent with the overall results derived from diffraction studies. The compressibilities of the lattices are calculated to be highly anisotropic, and the interdigitation of the alkyl chains on adjacent polymer chains are predicted to give rise to well defined polymorphs separated by high-energy barriers. The result is consistent with the lubricative effect of alkyl chain bilayers. The pressures calculated to be required to induce the occurrence of the appropriate phase changes (1-10 kbar) are close to those used in experimental investigations of pressure-induced changes in these polymer systems. Current theories of thermochromicity are tested by investigating the redistribution of excess conformational steric energy in the alkyl side-chains to the polymer backbone. Results indicate that the thiophene rings fold rather than twist around the polymer axis.