X-RAY STRUCTURAL STUDIES OF POLY(3-ALKYLTHIOPHENES) - AN EXAMPLE OF AN INVERSE COMB

X-ray diffraction studies of oriented poly(3-n-alkylthiophene) (P3AT's) solution-cast films show that these samples are characterized by well-organized lamellar structures whereby stacks of planar thiophene main chains are uniformly spaced by the alkyl side chains. In spite of considerable hydrocarbon chemical bonding and conformational disorder, a high degree of structural regularity is observed with appreciable three-dimensional ordering of the polymer chains. Analysis of the resultant scattering data in combination with model structure factor calculations leads to suggestive models in which an open packing of the alkyl chains is maintained with considerable side-chain disorder and side-chain mobility. There is evidence that this flexibility allows for an additional ordering process to occur at the interface formed by the alkyl side-chain end groups and that the liquid crystalline behavior is intimately related to the appearance of this structure.