Poly[3-(3',5'-di-tert-butyl-4'-acetoxyphenyl)thiophene] (la) was regioselectively synthesized via simple oxidative polymerization of 3-(3',5'-di-tert-butyl-4'-acetoxyphenyl)thiophene (2a) with ferric chloride. Head-to-tail content of la with a molecular weight of >10(4) reached 96% by modulating both the polymerization conditions and the purification procedure of the polymer. Visible absorption and fluorescence maxima were bathochromically shifted for both la and poly[3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)thiophene] (Ib), which suggests an extended pi -conjugation, i.e., a regioregular structure. Redox of the phenolate and of the thiophene residue of Ib was observed reversibly and independently under alkaline conditions. The polyphenoxyl 1 derived from the oxidation of Ib showed an electrical conductivity of 10(-5) S cm(-1). The polyradical 1 satisfies both an alternant but non-Kekule-type pi -conjugation and ferromagnetic connectivity of the unpaired electrons of the pendant phenoxyls. 1 with a spin concentration of 0.3 spin/unit displayed a spin quantum number (S) value of 2/2 to 3/2, indicating a high-spin ground state and an intramolecular ferromagnetic spin coupling through the polythiophene backbone.