Tuning Polythiophene Crystallization through Systematic Side Chain Functionalization

A study was conducted to demonstrate tuning of poly(3-alkylthiophenes) (P3AT) crystallization through systematic side chain functionalization. It provided detailed information about the thermal, structural, and electronic properties of a P3AT, poly(3-(20-ethyl)hexylthiophene) (P3EHT). Its properties were compared to two more common P3ATs, poly(3-hexylthiophene), and poly(3-dodecylthiophene) (P3DDT). Three different molecular weights of each type of polymer were synthesized and the molecular weights were controlled such that the average number of thiophene repeat units per chain was approximately the same between the P3HT, P3DDT, and P3EHT series. It was shown that P3DDT and P3EHT, with melting transitions sufficiently removed from the thermal degradation temperature, exhibited a nematic liquid crystalline phase observed by polarized optical microscopy (POM), with a molecular weight-dependent nematic-isotropic transition temperature.