WHISKERS OF POLY(3-ALKYLTHIOPHENE)S

It is shown that poly (3-alkylthiophene) s may readily crystallize fro m poor solvents in the form of whiskers. The experimental conditions r equired for the formation of whiskers were found to depend upon the al kyl 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 t he 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 whi skers was such that the polymer backbones were normal to the whisker l ength; that is, the b-axis was oriented parallel to the long axis of t he whiskers. These results are thought to be relevant to known thermoc hromism phenomena associated with poly (3-alkylthiophene) s.