Studies directed towards the step-growth photopolymerization of carbonyl compounds

Abstract

This thesis describes some work carried out in the relatively new area of step-growth photopolymerization of carbonyl compounds. The possibility of extending the photoreductive polymerization of aromatic diketones (leading to the synthesis of polybenzopinacols) to the photochemical synthesis of pentaphenylglycerols and higher analogues was investigated; however examination of the model photochemical reaction between benzophenone and triphenylglycol established that this glycol (and the related 1,2,2,2-tetraphenylethanol) is not a hydrogen donor for triplet benzophenone. In an attempt to examine the possibility of extending the photoreductive addition of benzophenone to diphenylmethane to polymer synthesis, m-dibenzoyl- benzene and m- and p-dibenzylbenzenes were prepared and characterized. Irradiation of the diketone in the presence of an equiraolar amount of either of the dibenzylbenzenes afforded low molecular weight products, shown by (^1)H and 13c n.m.r. spectroscopy to contain benzoplnacol, tetraphenylethane and 1,1,2,2-tetraphenylethanol type of units, in addition to benzophenone-type carbonyl and benzyl groups. Results obtained from the pyrolytic decomposition or treatment with dehydrating agents of one of the products were consistent with the proposed structure. Irradiation of tere- or iso-phthalaldehyde in the solid state yielded mostly starting materials whereas branched low molecular weight products were obtained from the irradiation of either of these aromatic dialdehydes in the presence of the hydrogen-donating isopropanol. An investigation on the structure of the 'photopolymer' produced on irradiating benzaldehyde in the liquid phase, by means of conventional spectroscopic analyses did not lead to a convincing structural hypothesis. 'Classical' chemical reactions proved to be more useful in this case; it was thus shown that the 'photopolymer', which has the same elemental composition as benzaldehyde but a molecular weight 9-11 times as high, can be acetylated, oxidized and is reactive towards sulphuric acid; it is furthermore stable to irradiation in benzene solution at 300nm in the absence of air and non-photo- reducible in isopropanol; it is however reduced by either sodium borohydrlde or sodium bis(2-methoxyethoxy)-aluminium hydride giving rise to a different structure in each case. Finally an extension of the Paterno-Buchi reaction of perfluoro compounds to polymer synthesis was attempted by examining the cycloaddition of perfluoroglutarylfluoride to two perfluoroolefins under a variety of experimental conditions. This work was largely unsuccessful and the rationalization of the results obtained will be found in the last Chapter of this thesis.