One-pot synthesis of poly-(3-hexylthiophene) with variable degrees of molar mass and regioregularity

Abstract

Polyalkylthiophenes are applied in the form of thin films as active layers in organic devices. The main properties defined in the synthetic procedure that can affect the film formation are the molar mass and regioregularity degree (the content of head-to-tail, HT, linkages). These properties can be varied, at principle, by changing the conditions of the oxidative polymerization process. In this work, we evaluate the effect of oxidant addition rate, temperature and time-dependence of poly-(3-hexylthiophene), P3HT, oxidative polymerization in molar mass and regioregularity degree, besides other polymer properties such as absorption and emission of visible light. The results show that the polymer started to grow during the oxidant addition and already presents a relatively high molar mass (ca. 10,000 g/mol) just after the addition stopped. Polymerization temperature is more significant in molar mass variations than the time expended for the polymerization reaction, with values of Mw ranging from 15,000 to 70,000 g/mol in the conditions tested. The HT contents were all above 70 %, with higher variations in the two first hours of polymerization reaction and are mainly defined during the oxidant addition, which leads to higher HT contents and narrower molar mass distributions using slower additions. The solvent extraction reveals that the HT content is directly related to the polymer chains extension, being possible to improve both regioregularity degree and molar mass of P3HT.