Dielectric, mechanical, thermal, rheological, and electron microscopy measurements are reported on the effect of varying the proportion of a blended thermoplastic, poly (ether sulfone), on the cure and properties of an epoxy resin system, an aromatic diamine cured trifunctional aromatic epoxide. Data presented cover both changes in physical properties during cure and final properties of the cured matrix. The initial mixture, prepared by solution casting, is homogeneous, but phase separation occurs rapidly in the initial stages of curing. Dielectric, thermal, and rheological measurements obtained during the curing process are consistent with phase separation occurring within the resin. Analysis of the dielectric data obtained from fully cured materials demonstrates the existence of a relaxation process which can be ascribed to polarization of a conducting occluded phase. Correlation of these data with those obtained from electron micrographs indicates that the type of phase structure changes with thermoplastic content. A number of the mechanical properties are observed to change at about 20-25% (w/w) of incorporated thermoplastic, coincident with the occurrence of a cocontinuous phase. The effects of these changes in the morphology on the mechanical, dielectric, and thermal properties of this thermoplastic-modified thermoset are discussed.

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Dynamic mechanical thermal analysis (DMTA) on a series of poly(ethersulfone)−amine-cured epoxy resin systems indicates phase separation is occurring, in agreement with previous electron microscopic and dielectric observations. Atomic force microscopy (AFM) measurements reveal that the surface roughness changes with composition and is greatest for the cocontinuous phase structure. Dielectric and gravimetric studies are reported on the absorption of water by these resin systems. Gravimetric measurements yield diffusion coefficients, obtained from the initial slopes, which vary slightly with thermoplastic composition. The equilibrium water uptake decreases with increasing thermoplastic content and when normalized by the volume fraction of epoxy resin exhibits a fairly constant value which infers that the majority of the water is dispersed in the epoxy phase. Analysis of the dielectric data at 10 Hz indicates that behavior similar to that obtained from gravimetric analysis is observed outside the cocontinuous phase region. At the cocontinuous composition, anomalous behavior was observed and is attributed to polarization phenomena associated with the microporous structure of the surface of these polymers. Dielectric analysis indicates that the relative rates of absorption depend on the frequency of observation and that there are two extreme types of environment present in these systems. Some of the water molecules are “bound” to hydroxyl groups generated in the cure process and others exist as “free” molecules in microcavities.

Differential scanning calorimetry (DSC) has been used to investigate the thermal transitions occurring for a series of Argonne Premium Coals. Two sets of experiments were conducted using different heating profiles to further examine a second-order transition which had previously been observed for Illinois No. 6 coal. Thermogravimetric analysis (TGA) was also conducted on the samples to support the DSC data. The DSC results show that on initial heating a first-order transition is observed which is a function of the cooling cycle and that subsequent scanning shows a clear and reproducible second-order process with the characteristics of a glass transition process. TGA shows that no mass loss is associated with either of these transitions.

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