A detailed study has been made of the thermal cure of two polyimides using infrared analysis. It is shown that two of the IR bands commonly used to determine the amount of imidization are affected by both interference from other species and by polymer morphology. These bands, located near 1780 cm−1 and 730 cm−1, overlap bands attributed to anhydride, which is formed when the polymer is heated. A correction for this effect is described. However, the measured absorbances of these bands are also subject to a dichroic effect. Any anisotropy in the samples can therefore affect the results. A third band, that located near 1370 cm−1, does not overlap anhydride peaks and did not, using the approach described here, display any effect due to dichroism. Thus it appears to offer a reliable way of following imidization by IR.

Films of poly(methyl methacrylate), of varying thicknesses from near monolayer to 2 gm, on gold and silicon substrates have been examined by external reflection infrared spectroscopy. The shape of the 1731 cm'1 C=0 band has been determined as a function of film thickness, angle of incidence, and polarization of the incident beam. Theoretical calculations of the band shape distortions of the C=0 stretching mode are in good agreement with the observed spectra. Additional calculations, based on indices of refraction calculated from the Kramers-Kronig relation, demonstrate the effects of wavelength, extinction coefficient, and bandwidth on hypothetical reflection spectra. Some general conclusions are drawn with respect to the types of shifts and distortions one can expect in the reflection spectra of typical organic polymer films. These results suggest that significant care be taken in the assessment of chemical changes from band shifts and splitting in polymer/metal reflection spectra.

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The photodimers formed by polycyclic aromatic hydrocarbons, such as anthracene, and their derivatives can be photodissociated to the original monomers. When the photodimer is held in a rigid matrix, the dimer can be remade efficiently because the two monomers are held in the proper relationship for photodimerization. The absorption spectra of monomer and photodimer differ substantially, and associated with this is a difference in refractive index. These characteristics as well as the stability of both states at room temperature make such a system attractive for reversible phase holographic recording with nondestructive readout. We have investigated several photodimer systems as solutions in rigid transparent polymer matrices, as well as some single crystals of photodimers. We have been able to write and erase diffraction gratings repeatedly. The photosensitivities ( 0.1 J cm(-2)), which are close to the maximum possible for a system with no gain, are high enough to be useful. Grating scattering efficiencies in the range of 0.01-5% have been observed. The physical, chemical, and photochemical characteristics of these systems, as well as some basic general considerations, are discussed.

SynopsisSolid samples of a nonhydrolytically stabilized bisphenol-A polycarbonate were hydrolyzed at 125°C and 1.4 atm of steam. IR and UV techniques were used both to estimate the degree to which the unhydrolyzed polymer is capped by a chain-terminating agent and to determine the rate of hydrolysis as indicated by the formation of new phenolic end groups. The rate of formation of lowmolecular-weight products, particularly bisphenol-A, was estimated by gel permeation chromatography studies. The combined results suggest that the degree of end-group capping is an important factor in the hydrolytic stability of the solid polymer. A model consistent with these results is proposed.