Hyperbranched copolymer containing triphenylamine and divinyl bipyridyl units for fluorescent chemosensors

A fluorescent hyperbranched copolymer (HTP) and a linear copolymer (PTP) as a reference sample to HTP both containing triphenylamine and divinyl bipyridyl units were synthesized via Heck coupling reaction from 5,5′‐Divinyl‐2,2′‐bipyridyl with tris(4‐bromophenyl)amine and with 4,4′‐dibromotriphenylamie, respectively. The chemical structure of HTP was confirmed by FTIR, ¹H NMR, and ¹³C NMR. The polymer HTP had a number‐average molecular weight of 1895 and a weight‐average molecular weight of 2315, and good solubility in conventional organic solvents, such as THF, DMF, and chloroform, and exhibited good thermal stability. The UV–vis absorption and photoluminescence (PL) spectra exhibited absorption maximum at 428 nm and emissive maximum at 531 nm for the HTP solution. The spectroscopic results of HTP and PTP indicated that hyperbranched conjugated structure increases the effective conjugation length, as compared with corresponding linear conjugated structure. The fluorescence of the polymer in solution can be quenched by various transition metal ions. The effect of backbone structure of the conjugated polymer‐based chemosensors on the sensitivity and selectivity in metal ions sensing have been investigated, and the quenching effect of HTP is more sensitive toward transition metal than linear copolymer PTP. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 222–230, 2009     

New confined p-phenylenevinylene (PPV)-type polymer analogue of poly(phenylene sulfide)

A new confined p-phenylenevinylene (PPV)-type polymer (PPVS) has been synthesized using Wittig condensation. The chemical structure of the polymer was well defined by ¹H NMR, ¹³C NMR, and FTIR spectroscopic analysis. PPVS contains oligomeric PPV units separated by sulfide bridges in the main chain; it is fully soluble in common organic solvents and has a number-average molecular weight of 3500 g mol⁻¹. Thermogravimetric analysis and differential scanning calorimetry indicate that PPVS is amorphous, stable up to 360 °C in air and displays a glass transition temperature of 98 °C. The optical properties of the polymer were investigated by UV-visible absorption and photoluminescence spectroscopies. The polymer film absorbs at 375 nm and emits at 517 nm with a narrow emission spectrum. From the cyclic voltammetry analysis, the electrochemical bandgap was estimated to be 2.78 eV. A single-layer diode device of the configuration indium-tin oxide/PPVS/aluminium has been fabricated and has a relatively low turn-on voltage of 3.4 V. An electroluminescent emission similar to photoluminescence is demonstrated in a multilayer device.     

The electrochemical detection of Ru(II) in a methyl methacrylate solution

This article describes the voltammetric behaviour of RuCl₂(PPh₃)₃ in a methyl methacrylate (MMA) solution. Acquiring this type of information is only possible when the ohmic resistance can be kept sufficiently low. Therefore, the conductivity study of pure methyl methacrylate and a tetrabutylammonium tetrafluoroborate (TBABF₄) methyl methacrylate solution has been described as well. Impedance measurements show an increase in conductivity by adding TBABF₄, while a conductometric curve illustrates the presence of ion pairs, triple ions and quadrupoles depending on the TBABF₄ concentration. The conductivity of a 0.1 mol L⁻¹ TBABF₄-MMA solution (formation of charged triple ions) was high enough to perform electrochemical experiments and a calibration curve could be obtained. The ability of obtaining relevant electrochemical data in low conducting media opens up new perspectives, especially for electroanalytical purposes used to monitor polymer reactions, more specific atom transfer radical polymerization (ATRP) reactions. This method employs a redox process with transition metal complexes in which a halogen ion is transferred reversibly between the transition metal and the polymer chain end. The dynamic equilibrium can be monitored by measuring the ruthenium concentration.     

Synthesis and properties of 6,6′-dithienyl-4,4′-bipyrimidine and its hetero- and homo-leptic Ru(II) complexes

Hetero- and homo-leptic Ru(II) complexes of a new 4,4′-bipyrimidine ligand, th₂bpm (6,6′-di(2″-thienyl)-4,4′-bipyrimidine), have been synthesized and characterized. The parent ligand th₂bpm has electron rich thiophene units on the periphery of a bidentate ligand which is capable of binding to metal ions. The heteroleptic complex of th₂bpm [Ru(bpy)₂th₂bpm]²⁺ (bpy = 2,2′-bipyridine) exhibits a Ru-to-bpm metal-to-ligand charge transfer (MLCT) absorption centered at 547 nm and a Ru-to-bpy MLCT absorption centered at 438 nm. The assignment of the low energy absorption is supported by the relative ease of electrochemical reduction of the new complex as compared to [Ru(bpy)₃]²⁺. The homoleptic complex, [Ru(th₂bpm)₃]²⁺, exhibits a Ru-to-bpm MLCT absorption at slightly higher energy (544 nm). Both complexes are emissive at room temperature in fluid solution and 5 is one of the lowest energy emitters based on tris-bidentate Ru(II) complexes known (λ_max = 770 nm). The luminescence spectra is red-shifted compared to [Ru(bpy)₃]²⁺ and this effect is ascribed to the delocalization in the acceptor ligand.     

Meltable phenylethynyl-capped oligoimide resins derived from 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene and 3,4′-oxydianiline

A series of meltable oligoimide resins with controlled molecular weights by reactive phenylethynyl endcapping groups have been prepared by the thermal polycondensation of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) with the aromatic diamine mixtures consisting of different mole ratios of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (1,4,4-6FAPB) and 3,4′-oxydianiline (3,4′-ODA) in the presence of 4-phenylethynylphthalic anhydride (PEPA) as molecular weight-controlling and reactive endcapping reagent. Experimental results indicated that the molecular weight-controlled oligoimide resins were mixtures containing a series of biphenylethynyl-endcapped oligoimides with different chemical structures and different molecular weights. The typical oligoimide resins could be melted at temperatures of 300 °C to yield stable molten fluid with melt viscosity of 13.4 Pa s, which was suitable for melt processing. The molten oligoimide resins could be further polymer chain extended and crosslinked by thermal curing of the reactive phenylethynyl groups to give strong and tough thermosetted polyimides. Thus, the oligoimide resin with calculated molecular weight of 2500 exhibited not only good meltability with low melt viscosity, but also high melt stability and fluidability at temperatures of <300 °C. After thermal curing, the obtained thermosetted polyimide showed high glass transition temperature (>316 °C, DMA), excellent thermal stability with initial thermal decomposition temperature of 588 °C and good mechanical properties with flexural strength of 159.1 MPa, flexural moduli of 3.3 GPa, tensile strength of 94.7 MPa and elongation at breakage of 9.0%.     

Synthesis and characterization of soluble polyimides derived from a novel unsymmetrical diamine monomer: 1,4-(2′,4″-diaminodiphenoxy)benzene

A new aromatic unsymmetrical diamine monomer, 1,4-(2′,4″-diaminodiphenoxy)benzene (OAPB), was successfully synthesized in three steps using hydroquinone as starting material and polymerized with various aromatic tetracarboxylic acid dianhydrides, including 4,4′-oxydiphthalic anhydride (ODPA), 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA), 2,2′-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride (6FDA) and pyromellitic dianhydride (PMDA) via the conventional two-step thermal or chemical imidization method to produce a series of the unsymmetrical aromatic polyimides. The polyimides were characterized by solubility tests, viscosity measurements, IR, ¹H NMR, and ¹³C NMR spectroscopy, X-ray diffraction studies, and thermogravimetric analysis. The polyimides obtained had inherent viscosities ranged of 0.38-0.58 dL/g, and were easily dissolved in common organic solvents. The resulting strong and flexible PI films exhibited excellent thermal stability with the decomposition temperature (at 5% weight loss) of above 505 °C and the glass transition temperature in the range of 230-299 °C. Moreover, the polymer films showed outstanding mechanical properties with the tensile strengths of 41.4-108.5 MPa, elongation at breaks of 5-9% and initial moduli of 1.15-1.68 GPa.     

Preparation of a new Cd(II)-imprinted polymer and its application to determination of cadmium(II) via flow-injection-flame atomic absorption spectrometry

A new cadmium(II)-imprinted polymer based on cadmium(II) 2,2′-{ethane-1,2-diylbis[nitrilo(E)methylylidene]} diphenolate-4-vinylpyridine complex was obtained via suspension polymerization. The beads were used as a minicolumn packing for flow-injection-flame atomic absorption spectrometry (FI-FAAS) determination of cadmium(II) in water samples. Sorption effectiveness was optimal within pH range of 6.6-7.7. Nitric acid, 0.5% (v/v) was used as eluent. Fast cadmium(II) sorption by the proposed material enabled to apply sample flow rates up to 10 mL min⁻¹ without loss in sorption effectiveness. Enrichment factor (EF), concentration efficiency (CE) and limit of detection (LOD, 3σ) found for 120-s sorption time were 117, 39.1 min⁻¹ and 0.11 μg L⁻¹, respectively. Sorbent stability was proved for at least 100 preconcentration cycles (RSD = 2.9%). When compared to non-imprinted polymer the new Cd(II)-imprinted polymer exhibited improved selectivity towards cadmium(II) against other heavy metal ions, especially Cu(II) and Pb(II), as well as light metal ions. Accuracy of the method was tested for ground water and waste water certified reference materials and fortified water. The method was applied to Cd(II) determination in natural water samples.     

Fluoride determination in some mouth wash preparations by a novel La(III) graphite coated membrane sensor based on amitraz

Solution studies on the binding properties of N-2,4-dimethylphenyl-N′-ethylformamidine (amitraz) toward nine lanthanide ions including lanthanum, cerium, neodium, samarium, europium, gadolinium, terbium, dysprosium, ytterbium and some other transition and heavy metal ions such as copper, lead, cobalt, nickel ions, showed a selective 1:1 complexation between amitraz and lanthanum ions. Consequently, amitraz was applied as an ion carrier in construction of a novel poly(vinyl chloride) membrane sensor for La(III). The sensor has a linear dynamic range of 1.0 × 10⁻¹ to 1.0 × 10⁻⁷ M with a Nernstian slope of 19.8 ± 0.2 mV per decade and a detection limit of 8.0 × 10⁻⁸ M. The proposed sensor displays a fast response time (<8 s), and can be used for at least 2 months without any considerable divergences in the potentials. The La(III) membrane sensor revealed comparatively good selectivity with respect to most of cations including alkaline, alkaline earth, and some transition and heavy metal ions. It could be used in a pH range of 3.0-9.0. The proposed membrane electrode was used as an indicator electrode in the potentiometric titration of La(III) ions with an EDTA solution, and also in the determination of fluoride concentration in some mouth wash preparations.     

Hg- and Cu-selective fluoroionophoric behaviors of a dioxocyclam derivative bearing anthrylacetamide moieties

New dioxocyclam derivatives bearing two anthracene fluorophores were prepared, and their fluoroionophoric properties toward transition metal ions were investigated. Chemosensor 2 having anthrylacetamide moieties exhibited pronounced Hg²⁺- and Cu²⁺-selective fluoroionophoric properties in aqueous acetonitrile solution over other representative transition metal ions, as well as alkali and alkaline earth metal ions. Chemosensor 2 also exhibited Hg²⁺ and Cu²⁺ selectivity under competitive conditions in the presence of physiologically and environmentally important metal ions. The detection limits for the sensing of Hg²⁺ and Cu²⁺ ions were 7.8 × 10⁻⁶ and 1.5 × 10⁻⁶ M, respectively, in aqueous 95% acetonitrile solution.     

Synthesis and properties of novel fluorinated epoxy resins based on 1,1-bis(4-glycidylesterphenyl)-1-(3′-trifluoromethylphenyl)-2,2,2-trifluoroethane

A novel fluorinated epoxy resin, 1,1-bis(4-glycidylesterphenyl)-1-(3′-trifluoromethylphenyl)-2,2,2-trifluoroethane (BGTF), was synthesized through a four-step procedure, which was then cured with hexahydro-4-methylphthalic anhydride (HMPA) and 4,4′-diaminodiphenyl-methane (DDM). As comparison, a commercial available epoxy resin, bisphenol A diglycidyl ether (BADGE), cured with the same curing agents was also investigated. We found that the BGTF gave the exothermic starting temperature lower than BADGE no mater what kind of curing agents applied, implying the reactivity of the former is higher than the latter. The fully cured fluorinated BGTF epoxy resins have good thermal stability with glass transition temperature of 170-175 °C and thermal decomposition temperature at 5% weight loss of 370-382 °C in nitrogen. The fluorinated BGTF epoxy resins also showed the mechanical properties as good as the commercial BADGE epoxy resins. The cured BGTF epoxy resins exhibited improved dielectric properties as compared with the BADGE epoxy resins with the dielectric constants and the dissipation factors lower than 3.3 and dissipation 2.8 × 10⁻³, respectively, which is related to the low polarizability of the C-F bond and the large free volume of CF₃ groups in the polymer. The BGTF epoxy resins also gave low water absorption because of the existence of hydrophobic fluorine atom.     

Electrochemical and electrochromic properties of novel aromatic poly(amine-amide)s derived from N,N′-bis(4-carboxyphenyl)-N,N′-diphenyl-1,4-phenylenediamine

A series of novel triphenylamine-containing aromatic poly(amine-amide)s were prepared from the dicarboxylic acid, N,N′-bis(4-carboxyphenyl)-N,N′-diphenyl-1,4-phenylenediamine, and various diamines by direct phosphorylation polycondensation. All the poly(amine-amide)s were amorphous, soluble in a variety of organic solvents, and could be solution cast into transparent, tough, and flexible films with good mechanical properties. They had useful levels of thermal stability associated with relatively high glass-transition temperatures (195-280 °C). These polymers exhibited strong UV-Vis absorption bands at 330-346 nm and their photoluminescence showed maximum bands around 516-535 nm in NMP solution. The hole-transporting and electrochromic properties are examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the poly(amine-amide)s prepared by casting polymer solution onto an indium-tin oxide (ITO)-coated glass substrate exhibited two reversible oxidative redox couples at potential 0.73-0.78 V and 1.12-1.18 V, respectively vs Ag/AgCl in acetonitrile solution. All the poly(amine-amide)s exhibited excellent reversibility of electrochromic characteristics by continuous ten cyclic scans between 0.0 and 1.40 V, with a color change from original pale yellowish neutral form to the green and then to blue oxidized forms.     

Synthesis characterizations and properties of a new fluoro-maleimide polymer

Novel 4-(4-trifluoromethyl)phenoxy N-phenyl-maleimide (FPMI) was synthesized. The free radical-initiated polymerization of FPMI was carried out in 1,4-dioxane solution using azobisisobutyronitrile as initiator. The monomer was investigated by FTIR, ¹H NMR, ¹³C NMR and elemental analysis, while the polymer was investigated by FTIR, ¹H NMR and ¹³C NMR. The effect of the monomer concentration, initiator concentration and temperature on the rate of polymerization (R_p) was studied. The activation energy of the polymerization was calculated (ΔE = 48.94 kJ/mol). The molecular weight of PFPMI and polydispersity index of the polymer were determined by gel permeation chromatography and were equal to 73,500, 16,700 and 2.27, respectively. The properties of PFPMI, including thermal behavior, thermal stability, the glass transition temperature (T_g = 236 °C), photo-stability, solubility and solution viscosity were studied.     

Electrochromic properties of novel strictly alternating poly(amine-amide-imide)s with electroactive triphenylamine moieties

A series of novel triphenylamine-containing aromatic poly(amine-amide-imide)s (PAAIs) were prepared by the phosphorylation polyamidation reactions from the diamine, N,N′-bis(4-aminophenyl)-N,N′-diphenyl-1,4-phenylenediamine, and various imide ring-preformed dicarboxylic acids. All the PAAIs were amorphous, had good solubility in many polar aprotic solvents, and exhibited excellent thin film forming capability with good mechanical properties. They displayed relatively high glass-transition temperatures (220-306 °C) and good thermal stability, with 10% weight-loss temperatures in excess of 522 °C in air or nitrogen and char yields at 800 °C in nitrogen higher than 66%. The solutions of polymers in NMP exhibited strong UV-vis absorption bands with a maximum around 315 nm. The hole-transporting and electrochromic properties were examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the PAAIs prepared by casting polymer solution onto an indium-tin oxide (ITO)-coated glass substrate exhibited two reversible oxidation redox couples at 0.63 and 1.01 V vs. Ag/AgCl in acetonitrile solution. All the PAAIs revealed very stable electrochromic characteristics, changing color from original pale brownish to green, and then to blue at 0.67 and 1.08 V, respectively.     

Nafion/2,2'-bipyridyl-modified bismuth film electrode for anodic stripping voltammetry

This paper describes the fabrication, characterisation and the application of a Nafion/2,2′-bipyridyl/bismuth composite film-coated glassy carbon electrode (NC(Bpy)BiFE) for the anodic stripping voltammetric determination of trace metal ions (Zn²⁺, Cd²⁺ and Pb²⁺). The NC(Bpy)BiFE electrode is prepared by first applying a 2.5 mm³ drop of a coating solution containing 0.5 wt% Nafion and 0.1% (w/v) 2,2′-bipyridil (Bpy) onto the surface of a glassy carbon electrode, while the Bi film was plated in situ simultaneously with the target metal ions at −1.4 V. The main advantage of the polymer coated bismuth film electrode is that the sensitivity of the stripping responses is increased considerably due to the incorporation of the neutral chelating agent of 2,2′-bipyridyl (Bpy) in the Nafion film, while the Nafion coating improved the mechanical stability of the bismuth film and its resistance to the interference of surfactants. The key experimental parameters relevant to both the electrode fabrication and the voltammetric measurement were optimized on the basis of the stripping signals. With a 2 min deposition time in the presence of oxygen, linear calibration curves were obtained in a wide concentration range (about 2-0.001 μM) with detection limits of 8.6 nM (0.56 μg dm⁻³) for Zn²⁺, 1.1 nM (0.12 μg dm⁻³) for Cd²⁺ and 0.37 nM (0.077 μg dm⁻³) for Pb²⁺. For nine successive preconcentration/determination/electrode renewal experiments the standard deviations were between 3 and 5% at 1.2 μM for zinc and 0.3-0.3 μM concentration level for lead and cadmium, respectively, and the method exhibited excellent selectivity in the presence of the excess of several potential interfering metal ions. The analytical utility of the stripping voltammetric method elaborated was tested in the assay of heavy metals in some real samples and the method was validated by ICP-MS technique.     

Hole-transporting [3,3′]bicarbazolyl-based polymers and well-defined model compounds

Polymers containing bicarbazolyl moieties in the main chain have been synthesized by the modified Ullmann coupling reaction from 9H,9′H-[3,3′]bicarbazolyl and different dihalo derivatives. The number-average molecular weights of the polymers synthesized were in the range of 2500-6200 with a molecular weight distribution of 1.6-3.1. Well-defined model compounds for the polymers have been synthesized by stepwise reactions. All these compounds have been found to form glasses with glass transition temperatures in the range of 57-119 °C as characterised by differential scanning calorimetry. The electron photoemission spectra of the compounds have been recorded and the ionisation potentials of 5.35-5.4 eV have been established. Room temperature hole drift mobility of the synthesized compounds molecularly dispersed in a polymer host range from 10⁻⁶ to 3 × 10⁻⁵ cm²/V s at an electric field of 10⁶ V/cm at the room temperature.     

Synthesis and characterization of novel fluorinated polyimides derived from 4-phenyl-2,6-bis[4-(4′-amino-2′-trifluoromethyl-phenoxy)phenyl]pyridine and dianhydrides

A series of organo-soluble polyimides were prepared from a novel fluorinated diamine monomer, 4-phenyl-2,6-bis[4-(4′-amino-2′-trifluoromethylphenoxy)phenyl]pyridine and various commercial aromatic dianhydrides. These polyimides had good solubility in common organic solvents. The obtained strong and flexible PI films exhibited excellent thermal stability with the decomposition temperature (at 5% weight loss) of above 561 °C and the glass transition temperature in the range of 258-312 °C. Moreover, the polymer films showed good electrical insulating property, low dielectric constant and low water uptake due to the introduction of fluorinated substitutes in the polymer backbone. The remarkable combined features ensure these polymers to be ideal candidate materials for advanced microelectronic industry and other related applications.     

Synthesis, characterization and photocrosslinking properties of polyacrylamides having bromo substituted pendant cinnamoyl moieties

New 3- and 4-bromocinnamoyl aniline were synthesized condensing 4-aminoacetophenone and the respective bromobenzaldehydes in the presence of sodium hydroxide. The monomers, 4-(3′-bromocinnamoyl) phenyl acrylamide (4,3′-BCPA) and 4-(4′-bromocinnamoyl) phenyl acrylamide (4,4′-BCPA) were prepared by reacting the respective chalcones and acryloyl chloride in the presence of triethylamine at 0-5 °C. Homopolymers of 4,3′-BCPA and 4,4′-BCPA was carried out in methyl ethyl ketone using benzoyl peroxide (BPO) under nitrogen atmosphere at 70 °C. The prepared polymers were characterized by UV, IR, ¹H-NMR and ¹³C-NMR techniques. The molecular weights (M_w and M_n) of the polymers were determined by gel permeation chromatography. The thermogravimetric analysis (TGA) of the polymers in nitrogen atmosphere reveals that they possess very good thermal stability required of a negative type photoresist. The glass transition temperature of poly(4,3′-BCPA) and poly (4,4′-BCPA) were found to be 55 and 64 °C respectively. The solubility of the polymers was tested in various polar and non-polar solvents. Photocrosslinking nature of the polymer samples was carried out in the presence and absence of various triplet photosensitizers in solution phase using chloroform solvent under medium frequency UV light. For using the polymers as negative photoresist materials the rate of photocrosslinking of the polymers was measured under the influence of different solvents, concentrations and position of the substituent.     

Removal of heavy metal ions from aqueous solutions by filtration with a novel complexing membrane containing poly(ethyleneimine) in a poly(vinyl alcohol) matrix

A novel complexing membrane was used for the removal of heavy metal ions such as Pb(II), Cd(II) and Cu(II) from aqueous solutions. The membrane consists in a semi-interpenetrating polymer network of crosslinked poly(vinyl alcohol) as the matrix and poly(ethyleneimine) as the complexing polymer. The absorption reactions followed pseudo-first-order kinetics with similar rate constants for the three cations. A model is proposed for the absorption–desorption process in order to rationalize the data obtained for the retention ratio and the retention efficiency ratio. The corresponding equilibrium constants were determined for the three metal ions, showing that the affinity order of the membrane is Pb > Cu > Cd. This sequence is consistent with the order of maximum uptake of the ions per gram of membrane: 0.59, 0.47 and 0.33 mmol g⁻¹, respectively. On the other hand, the uptake order is different on a mass basis: 123, 30 and 37 mg g⁻¹, respectively. Regeneration of the membrane and metal recovery were studied with HCl and HNO₃ at different concentrations. Filtration of solutions of each metal ion showed large elimination ratios (96–99.5%) with a retention sequence Cd > Cu > Pb. The membrane remained efficient until complete saturation of its sites. Moreover, Cu retention is larger than expected, indicating possible additional chelation by the PVA matrix. Better retention ratios were observed when the concentration of the feed solution was kept constant. Filtration of a mixture of the three cations (all at 100 ppm concentration) resulted in the same retention sequence, but the elimination ratios were smaller and Pb was eventually displaced by Cu and Cd that were present in larger molar concentrations.     

Synthesis and characterization of a π-conjugate, covalent layered network derived from condensation polymerization of the 4,4′-bipyridine-cyanuric chloride couple

Nucleophilic substitutions of the reactive chlorine atoms in cyanuric chloride by the bridging 4,4′-bipyridine in refluxing toluene lead to quaternarization of the latter and the subsequent formation of a π-conjugate, covalent layered network. The network is composed of central 1,3,5-triazine units with 4,4′-bipyridinium rings covalently attached and balanced by the released chloride ions. Due to the extremely high electron deficiency of the triazine rings, the material undergoes partial reduction by its compensated chloride ions resulting in a radical concentration of 1 × 10²⁰ spin g⁻¹, according to EPR quantitative analysis. In this instance, the radicals provide stability to the organic network by minimizing its electron deficiency. The material exhibits thermal and electrochemical stability, as evidenced by thermal gravimetric analysis (TGA) and cyclic voltammetry techniques. As such, the π-conjugate organic material displays low band gaps and electrical conductivity in the range of 10⁻⁴-10⁻⁵ S cm⁻¹ at room temperature.     

Aqueous solution behavior of p(N-isopropyl acrylamide) in the presence of water-soluble macromolecular species

We report here the polymerization of N-isopropyl acrylamide (NIPAM) via the reversible addition fragmentation chain transfer (RAFT) process. Two trithiocarbonates (S,S′-bis(α,α′-dimethyl-α″-acetic acid)-trithiocarbonate and 2-dodecylsulfanylthiocarbonylsulfanyl-2-methyl propionic acid) were used as the chain transfer agents in conjunction with 4,4′-azobis(4-cyanovaleric acid) and 2,2′azobis(2-methylpropionamidine) dihydrochloride as the initiating species. Poly(NIPAM) is a thermo-responsive polymer that has a sharp lower critical solution temperature (LCST). Herein, we investigated the aqueous solution behaviour of well defined p(NIPAM) prepared by the RAFT process as a function of molecular weight (degree of polymerization: 50, 100 and 200) and temperature. Furthermore, we examine the influence of varying concentrations of macromolecular species (neutral polyethylene glycol (M_n - 3400 g/mol) and ionic bovine serum albumin (M_n - 63 000 g/mol)) on the LCST of p(NIPAM). The aqueous solution behaviour was assessed by spectrophotometry, dynamic light scattering and surface tensiometry. The macromolecular additives was found to have a significant effect on the coil to globular transition of the lower molecular weight p(NIPAM).