Alan M. Kenwright

Low temperature synthesis of high molecular weight polyaniline

Abstract Oxidative chemical polymerization of aniline in hydrochloric acid solution at sub-zero temperatures leads to polyaniline with a molecular weight five to ten times higher than that prepared at room temperature. The optimum polymerization temperature to give a polymer with the highest yield and molecular weight has been determined, and solution state 13C n.m.r. spectroscopy shows that the improved polyaniline has fewer defect sites compared to the standard polymer. Despite these intrinsic improvements, the conductivity is of the same order of magnitude as standard polyaniline. A solvent-cast film of polyaniline camphorsulfonate had a conductivity of 295 S cm−1, although this rose to 820 S cm−1 along the stretch direction after the film had been uniaxially oriented. An oriented film cast from N-methyl-2-pyrrolidone solution and protonated with methanesulfonic acid showed a conductivity of 260 S cm−1 along the stretch direction and 31 S cm−1 perpendicular to this.

Changing the local coordination environment in mono- and bi- nuclear lanthanide complexes through “click” chemistry

Alkyne appended lanthanide complexes derived from DO3A undergo copper catalysed cycloaddition reactions with azides to form triazole appended complexes: coordination of one of the triazole nitrogen atoms to the metal centre changes the local coordination environment and the spectroscopic properties of the complex.

Quantitative aspects of solid state 13C n.m.r. of coals and related materials

Abstract The quantitative aspects of cross-polarization (CP), which is used in conjunction with dipolar decoupling and magic-angle rotation to obtain high resolution 13 C n.m.r. spectra of coals, have been studied using a bituminous coal (82 wt% C, dmmf basis) and asphaltenes from an extract of the same coal. The condition for obtaining reliable quantitative data, that rotating frame 1 H relaxation times ( T 1 p ′ these govern the extent of CP) are much longer than the time required to polarize the carbons present (≈1 ms), was met for the asphaltenes. In contrast, about half the protons in the coal have T 1 p 5 of ≈ ⩽ 1 ms, these times being too short to allow CP of all the carbons. Although the aromaticities obtained for this coal were fairly constant (≈0.75) using (CP) contact times > 0.5 ms, the total peak intensity decreased markedly as the contact time was increased and was much less than that for the asphaltenes. These results indicate that not all the carbons in bituminous coals are observed by CP and, as a consequence, aromaticities reported in the literature for some bituminous coals appear to be low.

Time-resolved near-IR luminescence from ytterbium and neodymium complexes of the Lehn cryptand

Abstract The Lehn cryptand has been widely applied to the study and application of luminescent lanthanide ions. We have demonstrated that the ytterbium and neodymium complexes are also luminescent. The luminescence lifetimes of the ytterbium complex fit well to established models for determining the number of inner sphere water molecules. By contrast, the neodymium complex exhibits unusually long lifetimes in aqueous media when compared to those observed with aminocarboxylate ligands. This behaviour may be ascribed to the relatively small number of proximate C–H oscillators in the cryptate.

Ring-opening metathesis polymerization of monocyclic alkenes using molybdenum and tungsten alkylidene (Schrock-type) initiators and 13C nuclear magnetic resonance studies of the resulting polyalkenamers

Abstract The ring-opening metathesis polymerization of a series of cycloalkenes initiated using well defined Schrock-type initiators is described. The products have been characterized by gel permeation chromatography, nuclear magnetic resonance and differential scanning calorimetry. The influence of initiator, reaction conditions and monomer structure is analysed in detail. The detailed microstructures of the polymers can be deduced from the 13C nuclear magnetic resonance spectra and apparent anomalies are accommodated in terms of the γ-gauche effect established by Tonelli.

Design Principles and Theory of Paramagnetic Fluorine-Labelled Lanthanide Complexes as Probes for 19F Magnetic Resonance: A Proof-of-Concept Study

The synthesis and spectroscopic properties of a series of CF(3)-labelled lanthanide(III) complexes (Ln=Gd, Tb, Dy, Ho, Er, Tm) with amide-substituted ligands based on 1,4,7,10-tetraazacyclododecane are described. The theoretical contributions of the (19)F magnetic relaxation processes in these systems are critically assessed and selected volumetric plots are presented. These plots allow an accurate estimation of the increase in the rates of longitudinal and transverse relaxation as a function of the distance between the Ln(III) ion and the fluorine nucleus, the applied magnetic field, and the re-rotational correlation time of the complex, for a given Ln(III) ion. Selected complexes exhibit pH-dependent chemical shift behaviour, and a pK(a) of 7.0 was determined in one example based on the holmium complex of an ortho-cyano DO3A-monoamide ligand, which allowed the pH to be assessed by measuring the difference in chemical shift (varying by over 14 ppm) between two (19)F resonances. Relaxation analyses of variable-temperature and variable-field (19)F, (17)O and (1)H NMR spectroscopy experiments are reported, aided by identification of salient low-energy conformers by using density functional theory. The study of fluorine relaxation rates, over a field range of 4.7 to 16.5 T allowed precise computation of the distance between the Ln(III) ion and the CF(3) reporter group by using global fitting methods. The sensitivity benefits of using such paramagnetic fluorinated probes in (19)F NMR spectroscopic studies are quantified in preliminary spectroscopic and imaging experiments with respect to a diamagnetic yttrium(III) analogue.

Transesterification in poly(ethylene terephthalate) and poly(ethylene naphthalene 2, 6-dicarboxylate) blends; the influence of hydroxyl end groups

Two samples of a single composition blend of PET and PEN were prepared by solution blending using different solvents such that the hydroxyl end groups in one blend were modified. The rate of transesterification in each blend was studied using proton NMR, an established technique for this system. The results indicate that the rate of transesterification is influenced dramatically by end group modification, providing clear evidence that hydroxyl end groups participate in the reaction mechanism.

Synthesis and Spectroscopic Studies on Azo-Dye Derivatives of Polymetallic Lanthanide Complexes: Using Diazotization to Link Metal Complexes Together

Heteronuclear tetrametallic lanthanide complexes have been synthesized from stable complexes by diazotization and azo-compound formation. Luminescence spectroscopy has been used to show that the complexes used as building blocks are stable under the reaction conditions.

A 13C n.m.r. study of transesterification in mixtures of poly(ethylene terephthalate) and poly(butylene terephthalate)

Abstract Poly(ethylene terephthalate) and poly(butylene terephthalate) homopolymers and mixtures of these two polymers have been heated in the absence of oxygen at 573 K for 30 min and 476 K for 6 h. The resultant polymers have been analysed using solution viscometry, d.s.c., density determination and 13C n.m.r. Degradation has been observed when the polyesters are heated at 573 K and this is particularly evident for the poly(butylene terephthalate). Assignment of resonances due to homogeneous and heterogeneous dyads and degradation products in the n.m.r spectra have been made using model compounds and a random copolyester which have been synthesized by us. Using these assignments we have calculated sequence length distributions of ethylene and butylene sequences in the materials obtained. On heating at 573 K transesterification of the polyester present in the minority is complete and a single random copolymer is obtained. From the melting point data, it is clear that two copolyesters result when the mixtures are heated at 476 K for 6 h. The values for the number average sequence length suggest that block copolyesters are produced.

Solution-state carbon-13 nuclear magnetic resonance studies of polyaniline

Abstract Solution-state 13 C nuclear magnetic resonance spectra are presented for the emeraldine base and leucoemeraldine base forms of polyaniline. The bulk of the leucoemeraldine base sample gives a simple two-line spectrum, which is readily assignable. The emeraldine base samples give spectra of much greater complexity, showing many more lines than there are carbons in the postulated chain repeat unit. This is rationalized in terms of slow interchange of the many conformers available to the emeraldine base form. A quantitative ‘region assignment’ is made. Gel permeation chromatography measurements show that interconversion between the two forms is achieved without either significant crosslinking or chain scission. The minor peaks in the spectrum of the leucoemeraldine base form due to chain defects (including chain ends) are compared with chemical shift values calculated for postulated structures, and some structures can be rejected on the basis of this.