Tailor made synthesis of water-soluble polythiophene-graft-poly(caprolactone-block-dimethylaminoethyl methacrylate) copolymer and their {pH} tunable self-assembly and optoelectronic properties

Here, we report a novel water-soluble polythiophene graft block copolymer i.e.; polythiophene-graft-poly(caprolactone-block-dimethylaminoethyl methacrylate)(PTh-g-PCL-b-PDMAEMA, P1) using combined polymerization techniques e.g. oxidative polymerization, ring-opening polymerization (ROP), atom-transfer radical polymerization (ATRP), and click chemistry; where pi-conjugated polythiophene (PTh) is situated as the main chain and polycaprolactone-block-poly(dimethylamino ethyl methacrylate) remains anchored from the PTh backbone. The final polymer was characterized by 1H NMR and FT-IR spectroscopy. Self-assembly behavior of the P1 polymer is investigated by high resolution-transmission electron microscopy and dynamic light scattering. Interestingly, both UV-vis and fluorescence emission peaks are shifted gently towards higher wavelength region for decreasing pH from 10 to 3, plausibly due to extension of PTh backbone caused by the repulsion of protonated -NMe2 group of grafted PDMAEMA segment. The results show variation of nanostructures from micelle to vesicle to multivesicular assembly with the variation of pH from 3 to 7 to 10. The dc-conductivity values at pH 3, 7, 10 are 0.40 +/- 0.09, 0.11 +/- 0.04, and 0.12 +/- 0.04 mu S/cm, respectively and the highest value at pH 3 is for the uncoiled polythiophene chain arising from the ionic repulsion of protonated -N(CH3)2 group of grafted PDMAEMA block. The I-V characteristic data shows semiconducting nature with signature of organic mixed electronic and ionic conductivity (OMEIC) at pH3.