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

Abstract

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.