WHISKERS OF POLY(3-ALKYLTHIOPHENE)S

It is shown that poly (3-alkylthiophene) s may readily crystallize from poor solvents in the form of whiskers. The experimental conditions required for the formation of whiskers were found to depend upon the alkyl side-chain length, solvent quality, and temperature. In all cases studied for alkyl side-chain lengths of 3-12 carbon atoms, the widths of the whiskers were of the order of 15 nm, while their lengths often exceeded tens of microns. The thickness of the whiskers formed under the experimental conditions employed was found to scale with side-chain length, and was approximately 2 or 3 times the a/2 lattice dimension of the polymer unit cell. Packing of the macromolecules within the whiskers was such that the polymer backbones were normal to the whisker length; that is, the b-axis was oriented parallel to the long axis of the whiskers. These results are thought to be relevant to known thermochromism phenomena associated with poly (3-alkylthiophene) s.