Stuart Anson Brewer

Diels–Alder chemistry at furan ring functionalized solid surfaces

A substrate-independent method for Diels-Alder chemistry at solid surfaces is described for the first time.

Quantitative NMR monitoring of liquid ingress into repellent heterogeneous layered fabrics

Fabrics which are water repellent and repellent to other liquids are often constructed using multiple layers of material. Such a construction is preferable to a single layer of a liquid-repellent textile because, under the action of an applied pressure, ingress of a liquid through the first layer can be halted by the second or subsequent layers. In the quantitative investigation of this problem, current techniques provide limited information on the progress and distribution of the liquid as it ingresses into a fabric. Moreover, many techniques require that the material is delaminated prior to analysis, and cannot be conducted in real time to measure the progress of a liquid through the textile substrate. In this work we demonstrate that unilateral NMR, which allows signal to be collected from a volume of interest in a material residing above the instrument, can be a powerful tool to quantitatively monitor the ingress of a liquid through a layered sample exhibiting pronounced heterogeneities in repellency. A known volume of oil was placed on the top of a model textile sample composed of three 80 microm thick layers. Spatially resolved one dimensional vertical NMR profiles of the system were acquired as a function of the pressure vertically applied to the top of the sample. These profiles show that the absolute liquid volume present in each layer of textile can routinely be measured within 4 min with a spatial resolution of 15 microm. If each individual layer exhibits different repellency to the test liquid, the complexity of the dynamics of the ingress can be investigated in great detail. An elegant application of the unilateral instrument was obtained in which the sensitive volume matched the region of interest of the individual layers of the textile under investigation.

Syntheses and crystal structures of Cu(II) and Zn(II) complexes of 2,2′-dipyridyl(N-propenyl)amine

Abstract Reaction between copper(II)- and zinc(II)-nitrates and 2,2′-dipyridyl(N-propenyl)amine (Prdpa) affords 1:1 complexes M(Prdpa)(NO3)2 (M=Cu, 1; M=Zn, 5) for both metal ions and a 1:2 adduct M(Prdpa)2(NO3)2 (2) for copper only. In ethanol 1 dissociates to form 2 and copper nitrate. X-ray diffraction studies on 1, 2 and 5, and on the 2,2′-dipyridylamine (Hdpa) analogue of 1, Cu(Hdpa)(NO3)2 (4), are reported. The metal centres exhibit square pyramidal (1) or distorted octahedral (2, 4, 5) primary coordination spheres. Bridging nitrate groups linking Cu atoms in 1 and 4 result in CuONOCu chains, which in the case of 4 are extensively cross-linked by N−H⋯ONO2 H-bonding into 3D-arrays. Intermolecular C−H⋯ONO2 interactions are apparent in the solid-state structure of 2. The structural effects of replacing the NH atom on Hdpa by a propenyl group in 6-coordinate Cu(II) complexes are assessed.

Synthesis of model organosiloxanes containing perfluoroether side-chains

A series of organotrisiloxanes [(Me3SiO)2MeSi(CH2)nO(CH2)mRf], (n = 3, m = 1, Rf = CF3; n = 3, m = 2, Rf = C4F9, C6F13, C8F17, C10F21, C7F15; n = 5, m = 1, Rf = CF3; n = 10, m = 0, Rf = C3HF6; n = 10, m = 1, Rf = CF3) have been prepared by the [Pt(cyclooctadiene)Cl2] catalysed hydrosilylation reaction between heptamethyltrisiloxane and CH2CH(CH2)n−2O(CH2)mRf. Yields are dependent upon the alkene chain length and degree of branching of the Rf group. Isomeric products [(Me3SiO)2MeSi(CH2)3OCH2CF3] and [(Me3SiO)2MeSiCH(Me)CH2OCH2CF3] were detected in reactions involving CH2CHCH2OCH2CF3 only.

The influence of humidity on the protective performance of a membrane based on poly(vinyl alcohol)

A solid-state NMR study has been used to rationalize the way humidity affects the barrier properties of a polyvinyl alcohol-based membrane. Polymer blends composed of polyvinyl alcohol–polyethyleneimine (PVOH–PEI) and polyvinyl alcohol–polydiallyldimethyl ammonium chloride (PVOH–PDADMAC) were investigated. At 90% relative humidity the PVOH–PEI material retains a PVOH-rich component that is detected in a cross-polarization NMR experiment and is therefore assumed to be relatively immobile. The barrier properties of this material are also largely retained at this relative humidity. Under the same conditions of humidity no signal is detected in the cross-polarization NMR experiment for the PVOH–PDADMAC system and the barrier properties of the PVOH–PDADMAC system are compromised. The persistence of the more rigid domains in the PVOH–PEI material is used to explain the barrier properties of this blend at high relative humidity. For the PVOH–PDADMAC system the cross-polarization signal is recovered and the barrier properties of the blend are restored to their original level as the humidity is lowered.

Synthesis of a series of dichloroamino- and dihalosulfonamido-1,3,5-triazines and investigation of their hindered rotation and stereodynamic behaviour by NMR spectroscopy

Mono-substituted 1,3,5-triazines (s-triazines) have been prepared and characterised by NMR spectroscopy. The room temperature 13C NMR spectra of dichloroamino-s-triazines show three signals for the triazine ring, clearly indicating that C(2) and C(3) are in inequivalent environments. At elevated temperatures, two of the signals broaden and coalesce. Conversely, a number of dihalosulfonamido-s-triazine compounds were found to display only one signal for C(2) and C(3), indicating that the degree of π-bonding in the exocyclic C–N bond in these compounds is less significant. The low temperature exchange limits for the dihalosulfonamido-s-triazine compounds are reported.