Unsaturated polymers containing boron and thiophene units in the backbone

2,5-Dialkynylthiophenes (RCC)2C4H2S (R = Ph, Me3Si or But) treated successively with HBCl2 and Et3SiH in CH2Cl2 undergo hydroboration polymerization to give intensely-coloured polymers of general structure –[CHCR–BCl–CRCH–C4H2S]n– for which the 11B NMR resonances occur ca. 50 ppm upfield of those for analogous monomers.