On the influence of regioregularity on the structural properties of poly(alkylthiophenes)

We present an overview of thorough, X-ray diffraction studies of the crystalline structure and conformation of the series of poly(alkylthiophenes) (PATs) samples. Three types of polymers have been subjected io these studies: ''common'' PATs, with ca 80% ''head to tail'' couplings; regioregular, pure ''head to tail'' PATs, and regioregular, pure ''head to head, tail to tail'' poly(4,4'-dialkyl-2,2'-bithiophenes). The samples containing n-hexyl, n-octyl and n-decyl groups have been investigated. The computer modelling has been intensively used in order to interpret the diffraction data. The results obtained show the importance of the coupling sequences on the structural properties of the polymers studied. The main effect is related to the average torsion angle between two adjacent thiophene rings: it exhibits a rather low value for the ''head to tail'' and ''tail to tail'' couplings, but it is remarkably higher for the ''head to head'' couplings. This leads to the important relations between the planarity and the crystallinity of all samples studied.