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Communications ADVANCED MATERIALSAs a result of this study some of the properties of alkoxysubstituted polythiophenes appear to be more understandable: a) It is not surprising that the regiochemistry of the substitution of linear alkoxy groups does not affect the conjugation length and the conductivity, as these substituents do not disturb the planarity of the main chain and of the overall conformation but rather favor it, at least with the substitution patterns so far discussed. b) The same influences tend to preserve, and possibly increase, the rigidity of the main chain, resulting in a packing stability which is greater than expected. In this way we can account for the lower solubility and higher melting points of alkoxythiophene oligomers and polymers compared to their alkyl-substituted analogues.[6* 'I ExperimentalThe detailed synthesis of the two isomers is reported elsewhere [3]. Crystals of both compounds used for all diffraction studies were obtained by crystallization from hexane. Thermal studies were performed with a Perkin-Elmer DSC-7 equipped with a CCA7 liquid nitrogen cooling device.