Sanjoy Samanta

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.

Polythiophene-g-poly(dimethylaminoethyl methacrylate) doped methyl cellulose hydrogel behaving like a polymeric AND logic gate

The variation of photoluminescence (PL) property of polythiophene-g-poly(dimethylaminoethyl methacrylate) (PT-g-PDMA, PD) with temperature and pH is used to develop a fully polymeric fluorescent AND logic gate type material using methyl cellulose (MC) hydrogel. The PL intensity gradually increases with increasing temperature of the PD doped aqueous MC solution and with increasing pH of the medium. In contrast, the PL-intensity of the PD solution decreases with increase in temperature for all of the pH values studied here due to collapsing of PDMA chains on the PT core, signifying that the PL intensity increases in the MC gel after compensating for the above decrease. The truth table suggests that it acts as an AND fluorescent molecular logic gate type system with fluorescence as output and temperature and pH as inputs. The maximum sensitivity of this logic gate is at higher pH (pH 9.2) than at neutral or acidic pH (pH 4) and at 45 °C. The reason is discussed from the viewpoint of the change in polarity at the microenvironment of the polythiophene chain in PD in the MC gel due to the change in temperature and pH.

Preventing Alkyne–Alkyne (i.e., Glaser) Coupling Associated with the ATRP Synthesis of Alkyne-Functional Polymers/Macromonomers and for Alkynes under Click (i.e., CuAAC) Reaction Conditions

Alkyne-functional polymers synthesized by ATRP exhibit bimodal molecular weight distributions indicating the occurrence of some undesirable side reaction. By modeling the molecular weight distributions obtained under various reaction conditions, we show that the side reaction is alkyne-alkyne (i.e., Glaser) coupling. Glaser coupling accounts for as much as 20% of the polymer produced, significantly compromising the polymer functionality and undermining the success of subsequent click reactions in which they are used. Glaser coupling does not occur during ATRP but during postpolymerization workup upon first exposure to air. Two strategies are reported that effectively eliminate these coupling reactions without the need for a protecting group for the alkyne-functional initiator: (1) maintaining low temperature post-ATRP upon exposure to air followed by immediate removal of copper catalyst; (2) adding excess reducing agents post-ATRP which prevent the oxidation of Cu(I) catalyst required by the Glaser coupling mechanism. Post-ATRP Glaser coupling was also influenced by the ATRP synthesis ligand used. The order of ligand activity for catalyzing Glaser coupling was: linear bidentate > tridentate > tetradentate. We find that Glaser coupling is not problematic in ARGET-ATRP of alkyne-terminated polymers because a reducing agent is present during polymerization, however the molecular weight distribution is broadened compared to ATRP due to the presence of oxygen. Glaser coupling can also occur for alkynes held under CuAAC reaction conditions but again can be eliminated by adding appropriate reducing agents.

Nano-structured poly(3-hexyl thiophene) grafted on poly(vinylidene fluoride) via poly(glycidyl methacrylate)

Poly(vinylidene fluoride)-g-poly(glycidyl methacrylate)-g-poly(3-hexyl thiophene) (PGHT) co-polymer was synthesized using atom transfer radical polymerization (ATRP) of glycidyl methacrylate (GMA) on a poly(vinylidene fluoride) (PVDF) backbone in ethylene carbonate (EC), followed by the oxidative polymerization of 3-hexyl thiophene (3-HT) from the anchored thiophene unit in nitromethane. The poly(vinylidene fluoride)-g-poly(glycidyl methacrylate (PG) and PGHT graft co-polymers are characterized by 1H NMR, FTIR and GPC analysis. The PG graft co-polymer exhibits an open spherulitic morphology which further worsens with increasing polymerization time. In PGHT, P3HT exhibits nanosphere morphology of diameter 2.9–5.5 nm that decreases with increased PG polymerization time. The lamellar structure of PVDF deteriorates with the progress of PG polymerization, however, upon further grafting with P3HT the lamellar structure of PVDF reappears. In the PG co-polymers PVDF exists in the α-polymorph but in PGHT, it transforms into the piezoelectric β-polymorph. Both the PG and PGHT graft co-polymers exhibit high thermal stability. The PVDF melting point in the PG co-polymers has decreased by 12–19°. However, in PGHT the PVDF melting point remains the same and the P3HT melting point increases. In PGHT, the π–π* transition peak shows a small red shift emitting at 14–18 nm lower wavelength than that of pristine P3HT. The above spectral shift is attributed to the self organized structure of grafted P3HT chains in PGHT forming a nanosphere morphology. The dc conductivity of PGHT is lower than that of P3HT.

Nondestructive characterization of Li+ ion-doped multifunctional poly(vinylidene fluoride)-g-poly(dimethyl amino ethyl methacrylate) by impedance spectroscopy.

Poly(vinylidene fluoride) (PVDF)-graft-poly(dimethyl amino ethyl methacrylate) (PDMAEMA) (PD copolymer) is produced via atom transfer radical polymerization from PVDF solution in N-methyl-2-pyrrolidone. PD copolymer is doped with 1% and 5% (w/w) Li(+) ion to produce PDLi1 and PDLi5 samples, respectively. In PD copolymer, the crystalline structure of PVDF changes from α polymorph to a mixture of α and β polymorph, and it transforms completely to piezoelectric β polymorph on doping with 1% (w/w) Li(+) ion. The impedance behavior of PVDF changes on grafting, and that of the PD graft copolymer also changes with increasing Li(+) ion dopant concentration. In the Nyquist plots, PVDF exhibits a straight line character, and a curvature has appeared in the PD graft copolymer; on doping the latter with Li(+) ion (1% w/w), the curvature increases and a semicircle is completed on 5% Li(+) doping. Fitting the data from the Z-view program, the Ohmic resistance of PDLi1 is found to be 78 MΩ having capacitance with constant phase element (CPE) = 1.38 nF while for the PDLi5 sample the resistance decreases to16.1 MΩ with a small increase in CPE to 1.46 nF. The modulus plane plots for PDLi1 and PDLi5 samples also exhibit only one peak supporting the presence of only one equivalent resistance-capacitance circuit with constant phase element in both PDLi1 and PDLi5 samples. Both the impedance and modulus vs frequency plots of PDLi1 and PDLi5 samples exhibit a single Debye peak suggesting isotropic nature of the samples. For PVDF and PDMAEMA, ac-conductivity increases linearly with angular frequency, but in the case of PDLi1 and PDLi5 samples, it remains at first invariant in the frequency range 1-10(2) Hz, and above 10(2) Hz, an increase in conductivity with frequency occurs obeying the double power law. In the temperature variation of conductivity, PVDF exhibits its typical insulating nature, and in the PD graft copolymer, the conductivity decreases with increase of temperature (metallic-like behavior) due to gradual breaking of supramolecular interaction. The temperature variation of ac-conductivity of the Li(+)-doped PD graft copolymer suggests that both the ionic and supramolecular contributions of conductivity operate; the former increases and the latter decreases with rise in temperature showing a maximum. The temperature-dependent FTIR spectra of PDLi1 and PDLi5 samples support the gradual breaking of supramolecular interactions with increase of temperature.