Gabriel J. Buist

Solubility properties in polymers and biological media. II. A new method for the characterisation of the adsorption of gases and vapours on solids.

Henrys constants at zero solute pressure have been determined by the gas chromatographic peak shape method for twenty-two solutes on four adsorbents (Rohm and Haas Ambersorb XE-348F carbonaceous adsorbent at 323 and 373 K, Sutcliffe Speakman 207A and 207C at 323 K, and Calgon Filtrasorb activated carbon at 323 K). The limiting values of log KH have been analysed in terms of solute dipolarity (pi 2*), solute hydrogen-bond acidity (alpha 2), and basicity (beta 2), and a new solute parameter (log L16), the solute Ostwald absorption coefficient on eta-hexadecane. The multiple linear regression equation, SP = SP0 + l.log L16 + s(pi 2* + d delta 2) + a alpha 2 + b beta 2 where in this instance SP = -log KH, can be used to identify the nature of the solute-adsorbent interactions, and to predict further values of log KH. For the solutes and solids we have studied, only the l.log L16 term is statistically significant, and hence--log KH is proportional to l.log L16. It is concluded that interactions between the gaseous solutes (that include alcohols and amines) and the four adsorbents involve just general dispersion forces.

Preparation and characterization of imidazole–metal complexes and evaluation of cured epoxy networks

A series of copper complexes of epoxy-imidazole adducts have been prepared and characterized by 1H nuclear magnetic resonance (NMR) spectroscopy. Differential scanning calorimetry (DSC) was employed to investigate the thermal behaviour of the curing agents and to investigate the medium-term storage stability of a one-pot composition of a commercial epoxy resin when mixed with the complexes. The cure onset temperatures of the mixtures containing copper complexes are ca. 20–50 °C higher than those of the parent epoxy-imidazole adducts and the decrease of cure onset temperatures in the early stages of storage (up to 100 h) is less. The latent nature and improved storage stability of mixtures containing the copper complex were clearly demonstrated and confirmed by the viscosity behaviour of the catalysed mixtures of the commercial epoxy resins MY720 and MY750. 1H NMR and electron paramagnetic resonance (EPR) spectroscopy were employed to monitor the thermal decomposition of the copper(II) complexes, which were found to decompose at 120–130 °C and exist in equilibrium. Glass fibre-reinforced composite samples were prepared using a commercial epoxy resin cured with the complexes and their physico-mechanical properties were evaluated.

High temperature 1H NMR studies of epoxy cure: A neglected technique

SummaryBy reference to the reaction of a copper complex of phenyl glycidyl ether and 2-ethyl-4-methylimidazole, and Bisphenol A diglycidyl ether, 1H nuclear magnetic resonance spectroscopy at high temperature is shown to be an excellent and under-utilized method for measuring the degree of cure, enabling kinetic parameters to be obtained.

Comparative kinetic analyses for epoxy resins cured with imidazole–metal complexes

Proton nuclear magnetic resonance (1H NMR) spectroscopy experiments were carried out for a commercial epoxy resin system in [2H6]DMSO solution and in bulk. Good agreement was obtained between the secondary rate constants found for the epoxide polyetherification reaction when monitored by Fourier-transform infrared (FTIR) or 1H NMR spectroscopy in the bulk over the range of temperatures studied. This highlights the usefulness of the high temperature bulk NMR technique in kinetic studies of polymerization.

Kinetic and computer modelling of epoxy resin cure

Abstract The use of a combination of computer modelling and tritium radiolabelling is described as a technique for the investigation of the kinetics and mechanism of the autocatalytic reactions occurring in epoxy resin cure. Rate constants for substituted anilines reacting with phenylglycidylether have been derived and the effect of steric hindrance investigated. The program is described and its use in the explanation and understanding of the experimental data is illustrated.

The application of molecular simulation to the rational design of new materials: 1. Structure and modelling studies of linear epoxy systems

Abstract The variation in torsional angles for a model linear epoxy system was studied as a function of applied stress and temperature. It was found that all of the torsional angles demonstrate a population migration from a lower to a higher energy state upon the application of an external stress. Subtle changes in torsional angle values under these conditions result in large energy differences.

Kinetic and simulation studies of linear epoxy systems

The kinetics and mechanism of the reaction between Bisphenol-A phenylglycidylether (BADGE) and 1,2-dianilinoethane (DAE) has been studied by a radiochemical method using tritium as the label and also by gel permeation chromatography (GPC). In parallel with these studies molecular simulation has been used to build models of the linear polymers formed, and their physical and mechanical properties have been calculated. Cast resin samples of the polymer have been produced for experimental determination of the physical and mechanical properties and the results of these determinations have been compared with the calculated values. These were found to be in reasonable agreement.

Chemical models for the cure of epoxy resins: the influence of hydrogen bonding

The industrial cure of epoxy resins requires reliable kinetic models of the chemical reactions which are taking place during cure. We demonstrate here how a combination of novel radiochemical and numerical modelling techniques can provide information on both the rates and the important chemical details of the mechanism of epoxy cure when applied to more tractable chemical models.

Kinetic modelling studies of amine–epoxide reactions: application of radiochemical and numerical techniques

The reaction between phenyglycidyl ether and a series of primary aromatic amines has been studied under conditions where [epoxide][amines](conditions which we categorise as ideal) using a radio-high-performance liquid chromatography (HPLC) method that is shown to be very versatile and capable of wide application. The results show that the small amounts of water present in the reaction medium possess a catalytic role as do the hydroxylated species formed during the course of the reaction. The detailed information so obtained makes it possible to use numerical techniques so that a comparison can be made between a theoretical model and the actual experimental behaviour.

Chemistry of isocyanides. Part 2. Nucleophilic addition of hydroxide to aromatic isocyanides in aqueous dimethyl sulphoxide. Correlations of rate with a nucleophilicity function

A range of aromatic isocyanides has been found to undergo nucleophilic addition of hydroxide in aqueous dimethyl sulphoxide (DMSO) over the composition range 0–98.67 mol% DMSO. The rate of reaction increases as the aqueous content of the solutions is decreased. At compositions low in DMSO correlations of log kobs with H–+ log aw are linear with slopes of 0.47–0.50, while at higher levels of DMSO correlations are also linear, but with slopes of 0.73–0.90. The results are discussed in terms of a solvent-induced switch from a concerted to a stepwise mechanism. An unusually enhanced reactivity of m-nitrophenyl isocyanide is observed and possible explanations for this are considered.