Diblock and triblock copolymers of semiconducting poly(3-hexylthiophene) (P3HT) and side chain liquid crystalline methacrylates were synthesized with the combination of Grignard metathesis polymerization (GRIM) and atom transfer radical polymerization (ATRP). The azobenene (nematic) and biphenyl (smectic) liquid crystalline mesogens were incorporated into the diblock and triblock copolymers with semiconducting P3HT. Both azobenzene and biphenyl have thermotropic properties. In addition azobenzene has photo-responsive properties thus making resulting copolymers potential material for thermal and photo sensors. The effect of the supramolecular assembly on the opto-electronic properties of the resulting block copolymers was investigated. Improved long range ordering of polymer nanowires induce better π-π stacking of thiophene units which facilitates charge transport by hopping. This was depicted when the mesogen was switched from nematic to smectic where the hole mobility was increased by one order magnitude with the appearance of π-π stacking peak for biphenyl in XRD spectra of the resulted copolymers. The composition of synthesized copolymers was determined by 1H-NMR. Characterization of the thermotropic liquid crystalline behavior was done in a combined study with polarizing optical microscopy with heating stage and differential scanning calorimetry. The liquid crystalline mesophases of the copolymers appear above the glass transition of P3HT which helps long range ordering of P3HT by co-crystallization after annealing above the mesophase transitions. Soft and rubbery nature of the P3HT segment at mesophae transitions aid rearranging in to polymer nanowires. The effect on self-assembly and morphological changes of copolymers upon annealing was studied with tapping mode atomic force microscopy (TMAFM), thin film X-ray diffraction studies (XRD), and UV-VIS analysis. The field effect mobilities of the P3HT diblock and triblock copolymers were determined in organic field effect transistors (OFET). Mobilities as high as 10-2 cm2/Vs were measured.

Enhanced supramolecular self-assembly of P3HT by copolymerization with methacrylate attached liquid crystalline mesogens

251st National Meeting (2016)

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