John M. Barton

Mechanical properties of tough, high temperature carbon fibre composites from novel functionalized aryl cyanate ester polymers

Abstract Carbon fibre pre-impregnated tape (prepreg) was prepared from a range of prepolymers comprising blends of propenyl-functionalized cyanate ester (CE) oligomers with commercial bis-maleimide (BMI) monomers. Cured neat resin plaques and carbon fibre composites were prepared by autoclave moulding. Various blends of a commercial BMI mixture, a CE and a co-monomer with either allyl or propenyl and cyanate pendant groups were prepared. Differential scanning calorimetry (d.s.c.) data were used to monitor cure of neat resin, while dynamic mechanical thermal analysis (d.m.t.a.) was used to assess cure cycles of composite materials by the measurement of glass transition temperatures (Tg). Composite properties measured were interlaminar shear strength, flexural strength, compressive strength and Mode 1 Fracture toughness (GIC).

Some effects of structure on the cure of glycidylether epoxy resins

Abstract Three glycidylether epoxy resins with functionalities of 2, 3 and 4 were purified and extensively characterized. The cure of the resins with diaminodiphenylsulphone, both alone and as blends, was studied using rheometry and differential scanning calorimetry. The effect of resin functionality on the rate of cure was greater than would be expected from simple concentration effects. The kinetics were best described by an autocatalytic model over approximately the first 40% of reaction. Thereafter an n th order expression gave a better fit to the data. The modulus crossover point, t G ′ = G ″ , was found to be a reproducible indication of gelation, and the fractional conversions at this point, obtained by combining d.s.c. and rheology data, were compared to the values predicted by gelation theory. A model was used to predict the viscosity of samples during cure as an aid to processing.

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.

THE DEVELOPMENT OF CONTROLLABLE METAL-CHELATE CURING AGENTS WITH IMPROVED STORAGE STABILITY

SummaryThe novel latent epoxy curing agent and commercial epoxy system designated MY750/Cu(PGE-EMI)4Cl2 shows remarkable properties under both extended storage and cure conditions. For example, after a period of 2600 hours at ambient temperature the viscosity of an MY750/Cu(PGE-EMI)4Cl2 mixture is still low enough (ca.3x106 cps) to be measured at ambient temperature, while the corresponding MY750/(PGE-EMI) adduct mixture is too viscous to be measured (ca. 8x106 cps) after only 430 hours. The slower increase in viscosity of the complex mixture indicates that it is much more stable than its parent imidazole when dispersed in an epoxy prepolymer over an extended period of time. FTIR and 1H n.m.r. data suggest that after heating an MY750/Cu(PGE-EMI)4Cl2 mixture for 5 minutes at high temperatures (120–140°C) and a room temperature quench, almost no further cure occurs thereafter.

Physical ageing of an epoxy resin/polyethersulphone blend

Abstract An epoxy resin was blended with polyethersulphone. The enthalpy relaxation data obtained after annealing the neat cured resin and the blends at 180°C have been curve fitted to an equation which uses the Kohlrausch-Williams-Watts function. Such an approach may enable the prediction of the long term effects of ageing on the engineering properties of such materials.

Studies on a series of bis-arylimides containing four phenylene rings and their polymers: 3. Kinetic analysis of the thermal polymerizations

Abstract A series of aryl bis-maleimides (BMIs) and bis-citraconimides (BCIs) were characterized by d.s.c. using both temperature scans and isothermal experiments. Impurities in the BMIs tend to increase the temperature at which thermal polymerization starts, while the converse is true for BCIs. This was attributed to the presence of an itaconimide impurity in the BCIs. In particular, the thermal polymerization kinetics of the compounds were investigated. Effects of structure and monomer purity on the thermal polymerization characteristics were identified.

The synthesis, characterization and polymerization kinetic study of a series of related addition polyimides:

A series of eight addition polymides (aspartimides) was prepared in which the imide and amino groups were attached to the ends of aromatic residues containing two or four phenylene rings. The co-monomers (bis-maleimides. BMIs, and diamines) were purified using column chromatography before being fully characterized by spectroscopic techniques. The thermally induced Michael addition and polymerization reactions of the blended co-monomers were monitored using differential scanning calorimetry (Dsc) at several heating rates to enable the kinetics of the processes to be investigated. The thermal stabilities of the thermoset products of these aspartimides were evaluated by thermogravimetric analysis (TGA). Dynamic mechanical thermal analysis (DMTA) was employed to test the physical properties of the neat resins.

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.

A comparative study of the relative reactivity of alkenyl-functionalized toughening modifiers for bis-maleimides

SummaryA study of the copolymerization of HPLC-pure bis(4-maleimidophenyl)methane (DDM-BMI) with four alkenyl-functionalized aromatic comonomers using differential scanning calorimetry (DSC) and the effects of various catalysts on the reaction is presented. The added catalysts appeared to have little effect on the overall polymerization behaviour and the onset of reaction was largely governed by the fusion temperature of the DDM-BMI monomer. However, the maximum rate (during scanning at 10K/minute) was dependent on the structures of the alkenyl co-monomers.A study of the relative reactivity of ortho disbustituted allyl and propenyl bis-phenols employing DSC and dilute solution Fourier transform infra-red (FT-IR) spectroscopy is also presented. Attempts are made to reconcile the reactivity with the nature and orientation of the substitutents.