This article presents a comparison of data obtained from a low-temperature cure of an epoxy/amine system by three independent cure monitoring techniques: ultrasonic wave propagation, dielectric permittivity, and nuclear magnetic resonance. The sizes and thermal histories of the samples studied by the three techniques were controlled for comparability between the methods. The three techniques gave consistent information on the progress of cure and were complementary, in that each was particularly sensitive to different stages of the cure process.

The iron is displaced 0.48 A from the plane of the four nitrogens and 0.56 A from the mean porphyrin plane. The O-C bond of the methoxide is eclipsed with respect to one of the Fe-N bonds. The experimental electron distribution was determined by least-squares refinement including multipole deformation functions (R = 2.3%, Rw = 2.8%). Populations of the deformation functions in the carbon atoms of the porphyrin ligand agree well with those found previously in (mero-tetraphenylporphyrinato)cobalt(II), which suggests transferability of ligand density between complexes. An approximately spherical electron distribution is found at the iron site, and experimental d-orbital occupancies calculated for the iron atom from the deformation populations are consistent with a high-spin Fe(III) state. However, small but significant deviations from spherical symmetry are observed which, together with observed net atomic charges, have been used to calculate a Móssbauer quadrupole splitting constant of +0.6 (3) mm/s.

In this study, the glass transition temperature Tnormalg is determined from thermal expansion measurements in a series of glass compositions prepared by bulk fusion of a phosphosilicate matrix to which oxides of boron, germanium, or arsenic are added. On a per‐molar basis, addition of boron was observed to be the most effective in lowering the glass transition temperature of the phosphosilicate matrix, as compared to arsenic or germanium, which is found to be the least effective. For borophosphosilicate glass with concentrations of B2O3 less than 13 m/o, values of Tnormalg are observed to be reduced by increasing the P2O5 content. Near 13 normalm/normalo B2O3 the temperatures become independent of P2O5 , while at a still higher B2O3 content they are actually raised upon increasing the P2O5 concentration. For the germanophosphosilicate glass, no such reversal is noted as values of Tnormalg decrease slightly with P2O5 , additions at all GeO2 concentrations. Glass compositions with potential VLSI applications can, thus, have the P2O5 content reduced to the minimum value required to provide gettering without significantly affecting the glass transition or associated viscous flow parameters. From a comparison of the measured values of Tnormalg in bulk glasses with reported values of the flow temperature Tf for films with corresponding compositions, a correlation factor relating those two parameters is established. Thus, the relatively simple thermal expansion technique can now be used to survey for glass compositions with promising flow characteristics without the rigorous and time consuming effort of conducting the more difficult bulk viscosity experiments or developing deposition processes for films with possibly unsuitable viscous characteristics.

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The tracking of the cure of epoxy adhesives and the assessment of the cure state of adhesive bondlines joining engineering components are important for quality assurance during manufacture and for the safe functioning of manufactured assemblies in the field. Ultrasound can be used to give estimates of the compression modulus of curing and cured materials and thereby provide a means to assess non-destructively the cure state of adhered joints during manufacture and in service. These techniques are at present difficult to apply and are predominantly empirical in that little is known about the relationships between the measured ultrasound data and the evolving molecular structure of the adhesive as it cures. The present paper describes the application of a group of physical techniques that can be used to characterise the polymer structure during cure, with the aim of relating these to phenomena measurable by ultrasound. Wide angle X-ray scattering (WAXS) provides a basic measure of polymer chain formation, which is seen to correlate closely with the compression modulus as it develops during cure. Low resolution nuclear magnetic resonance (NMR) provides a means to observe the mobility of bound hydrogen nuclei and thereby to track the change in state of a resinhardener system from a viscous liquid to a crosslinked solid. The NMR data obtained during cure correlated well with compression modulus development. Ultrasonic shear wave spectrometry indicates when a curing material can first support shear motions and this agrees well with NMR data and with specifications of gel point given by manufacturers. Ultrasonic compression wave absorption data provide frequency dependent patterns that change during the cure cycle and that can be explained on the basis of the results of the WAXS, NMR, and shear wave experiments. These changing patterns have potential for tracking cure using low cost ultrasonic techniques, the results of which can be related to phenomena taking place on a molecular scale.PRC/1575