Electrochemical and chemical polymerization of acrylamide

The electrochemical and chemical polymerization of acrylamide (AA) has been studied. The electrolysis of the monomer in N,N-dimethylformamide (DMF) containing (C₄H₉)₄NClO₄ as the supporting electrolyte leads to polymer formation in both anode and cathode compartments. The cathodic polymer dissolves in the reaction mixture and the anodic polymer precipitates during the course of polymerization. A plausible mechanism for the anodic and cathodic initiation reaction has been given. The chemical polymerization of acrylamide that has been initiated by HClO₄ is analogous to its anodic polymerization. The polymer yield increases with an increase in concentration of the monomer and HClO₄. Raising the reaction temperature also enhances the polymerization rate. The overall apparent activation energy of the polymerization was determined to be ca. 19 kcal/mole. The copolymerization of acrylamide was carried out with methyl methacrylate (MMA) in a solution of HClO₄ in DMF. The reactivity ratios are r₁ (AA) = 0.25 and r₂ = 2.50. The polymerization with HClO₄ appears to be by a free radical mechanism. When the polymerization of acrylamide is carried out with HClO₄ in H₂O, a crosslinked water-insoluble gel formation takes place.     

Synthesis,Spectral and Structural Studies of a Novel Semicarbazone Synthesized from Quinoline-2-Carboxaldehyde and N<Superscript>4</Superscript>-Phenyl-3-Semicarbazide

Abstract  

A new semicarbazone, HL has been synthesized from quinoline-2-carboxaldehyde and N⁴-phenyl-3-semicarbazide and structurally and spectrochemically characterized. ¹H NMR, ¹³C NMR, IR and electronic spectra of the compound are studied. The existence of keto form in the solid state is supported by the crystal structure and IR data. The compound crystallizes into an orthorhombic space group P2₁2₁2₁. Intra and intermolecular hydrogen bonding interactions facilitates unit cell packing in the crystal lattice.     

Preparation and characterization of 1,2,3‐triazole‐cured polymers from endcapped azides and alkynes

Fourteen commercial polyols have been characterized by GPC, NMR spectroscopy, and elemental analysis. From these, eight corresponding tosylates, six nitrate esters, seven mesylates, 13 alkynes, and 14 azides have been prepared and all these derivatives have been fully characterized. Five alkyne monomers and eight azide monomers were also prepared. Twelve alkynes and 13 azides (functionality 2–4) were combined in 1,3‐dipolar cycloaddition reactions under neat conditions to prepare triazole‐cured polymers, avoiding any heavy metal catalyst. Characterization by NMR spectroscopy, elemental analysis, and gel permeation chromatography indicated triazole polymers 14 , 22 , 23 , 28 , and 30 with degrees of polymerization of 17–28 to be the best candidates for future work. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 238–256, 2008     

Colorimetric and fluorescence sensing of fluoride anions with potential salicylaldimine based schiff base receptors

Salicylaldimine based schiff base receptors with different substituents showing fluorescent enhancement in the presence of fluoride anion was visualized through naked eye as well as by change in spectral properties (UV–vis and fluorescent techniques). The reason for such fluorescence enhancement may be due to hydrogen bond interaction between receptor recognition site and fluoride anion. Such a hydrogen bond interaction creates a six-membered transition state, which avoids quenching processes. To support this, fluorescence enhancement factor (FEF) was calculated and it was found to be more (FEF = 652) for –NO₂ substituted receptor compared to other receptors.     

Synthesis of Boltorn 1,2,3‐triazole dendrimers by click chemistry

Second‐, third‐, and fourth‐generation hyperbranched aliphatic polyols namely Boltorn® H20, Boltorn H30, and Boltorn H40 were endcapped with azido and activated acetylenic groups in good to excellent yields (75–95%) following an acid catalyzed procedure. The resultant terminally functionalized dendritic azido and acetylenic groups undergo 1,3‐dipolar cycloaddition using methyl (or ethyl) propiolate and benzyl azide, respectively, under catalytic or noncatalytic conditions below 40 °C to yield 1,2,3‐triazole dendrimeric polymers in 82–95% yield, under extremely mild conditions that could be applied for compounds sensitive to acid, base, or heat. The dendritic azido and activated acetylenic derivatives may act as novel scaffolds to tune the mechanical properties of different polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3748–3756, 2009     

Electrochemical anionic polymerization of 4-vinylpyridine in pyridine

The preparation of poly-4-vinylpyridine (poly-4VP) by electrochemical polymerization of 4-vinylpyridine (4VP) in pyridine containing sodium tetraphenylboron (NaBPh₄) is described. Information on the influence of monomer concentration, current density, polymerization rate, molecular weight, and electrochemical efficiency is presented. The polymerizations were performed under conditions of constant electrolysis current. Polymer formed in the cathodic compartment only, where a red-orange solution developed after about 15 min of electrolysis time. The optical absorption spectra of these colored solutions were studied. Cyclic voltammograms of 4VP in pyridine and NaBPh₄ are also reported, and the influence of the scan rate upon peak current is described. The results indicate that the polymerization was anionic and nonterminating. The characteristics of the electrochemical polymerization of 4VP in pyridine are compared with those of the same monomer in liquid NH₃. In the former case, the catholyte was homogeneous, and polymer growth occurred in the liquid phase, while in the latter growth took place in a heterogeneous environment. Kinetic consequences of these physical differences are pointed out. Suggestions for the mechanism of this electrochemical initiation are advanced.     

Kinetics of receptor directed assembly of multisegment nanowires

We demonstrate the receptor directed end-to-end assembly of multisegment Au/Ni/Au nanowires under agitation in ethanol. The gold end-segments were functionalized with biotin-terminated thiol thereby restricting aggregation to end-to-end attachment via an avidin linkage. On mixing biotin-terminated nanowires with avidin-terminated nanowires, the average chain length is shown to increase linearly with time. The rate constant was independent of the nanowire concentration. Kinetic Monte Carlo simulations were used to model the self-assembly process, and we show that the directed end-to-end assembly of nanowires is similar to the polycondensation of linear polymers.