Thermo and pH responsive water soluble polythiophene graft copolymer showing logic operation and nitroaromatic sensing

A polythiophene based water soluble thermo and pH responsive graft copolymer is prepared by anchoring the initiator moiety (2-bromoisobutyryl bromide) on 3-thiophene ethanol and polymerizing using ferric chloride to produce the 2,5-poly(3-[1-ethyl-2-(2-bromoisobutyrate)]) thiophene macroinitiator (PTI), followed by polymerization with a mixture of varying composition of diethyleneglycol methylether methacrylate (MeO2MA) and N,N-dimethyl aminoethyl methacrylate (DMAEMA) at 30 °C using copper based atom transfer radical polymerization (ATRP). The polymers are characterized by gel permeation chromatography (GPC) and by 1H NMR spectroscopy. Polythiophene-g-P(MeO2MA-co-DMAEMA) (PTDM) exhibits considerable water solubility but due to the lower critical solution temperature (LCST) of aqueous PMeO2MA at ∼26 °C the particle sizes observed by dynamic light scattering (DLS) show a sharp increase in the region 25–30 °C only for a pH value of 9.2. However, at lower pH values (pH 4 or 7), in the LCST region of PMeO2MA there is no increase of particle size. The TEM micrographs of PTDM indicate core–shell morphology at pH4 and pH7 with a gradual decreasing of the size (with PT at the core and P(MeO2MA-co-DMAEMA) at the shell), and at pH 9.2 no core–shell morphology is observed due to the absence of protonation at the –NMe2 groups of the PDMAEMA segments. The fluorescence intensity of the PTDM solution at pH 9.2 also shows a sharp increase in the temperature range 22–29 °C, but remains almost without change at pH 4 and 7. Using the pH and temperature as inputs and the fluorescence intensity as an output, the system functions as a fully polymeric AND logic gate, and this is the first report using polythiophene as the fluorescence probe. Also PTDM in the solid/solution state exhibits considerable quenching of fluorescence intensities in the presence of nitroaromatics such as picric acid, dinitro phenol, etc. and may be used for sensing nitroaromatics.

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