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Abstract

Polymers containing chromophores based on l,3-diphenyl-prop-2-en-l-one (chaicone) undergo photocrosslinking when irradiated with UV light. This photocrosslinking reaction was followed using four different spectroscopic techniques.

UV/visible photoacoustic spectroscopy was used to try and assess the degree of cure in the polymer film. Some changes in the spectra of the polymers were observed. However it was shown that this technique can-not be used for quantitative work since the PA signals exhibit saturation. The highly absorbing nature of the polymers and the limited modulation frequency range of the instrument, meant that this problem of saturation was insurmountable.

Depth profiling of some samples was achieved by variation of modulation frequency.

A signal occurring 90° out of phase with the main signal was attributed to reflection of heat from the sample - substrate boundary.

A simple statistical model was derived, which indicates that polymers based on chaicone should have the same number of unreactive sites as polymers containing the photoreactive cinnamate group. However polymers based on 1,5-diphenyl-pent-1,4-dien-3-one should have fewer unreactive sites.

The use of IR transmission spectroscopy proved useful for comparing rates of reaction of polymers containing different concentrations of the same chromophore and of polymers containing different chromophores. Irradiation generated a concentration gradient, this made it impossible to determine absolute rates. A kinetic model was devised in which at-tempts were made to account for concentration of unreactive sites and for the development of concentration gradients.

The IR spectra indicate that the statistical model predictions of un-reactive sites are too high.

More information about the absorption bands of the polymers, in the UV/ visible region was obtained by diffuse reflectance spectroscopy, particularly at low wavelengths. The polymers exhibit a short wave-length absorption band which was not found in solution spectra. This band disappears on irradiation and was tentatively assigned to an inter- molecular interaction in the solid phase.

Well resolved IR spectra of small samples were obtained using FT-IR-PAS, powders gave even better spectra than films. However band intensities in the FT-IR-PA spectra were found to be different to those in trans-mission IR spectroscopy. These differencies were attributed to the thermal diffusion depth varying with frequency in FT-IR-PAS.

An attempt was made to use FT-IR-PAS to depth profile polymer films, but this was found to be a difficult process due to it not being clear as to whether operating under saturation conditions or not.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science T Technology
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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