Labile polycarbonates containing azo units susceptible to thermolytic or acidolytic degradation

Abstract

Co- and terpolycarbonates containing thermosensitive cycloallylic, benzylic or tertiary diols and, in addition, labile azo functionalities were synthesized in solution from bis(imidazole-carboxylate)s under phase-transfer conditions. The azo groups were introduced by using 2,2'azobis(2-methylpropanol) (1) and azobis(1-hydroxymethyl)cyclohexane (2) as diol components. All copolymers were obtained as amorphous, soft materials with glass transition temperatures below 30°C. Partial crystallinity, however, could be obtained in terpolycarbonates, leading to improved mechanical stability of the products. The polymers were obtained with molar masses Mn in the range 6000-12 900 g/mol. Depending on the structure, the polymers decomposed between 180 and 220°C in a clean, fast, and exothermic process, liberating mostly volatile products. The thermal lability of the azo moieties 1 and 2 was similar to that of the labile carbonate units. In the presence of acids, the thermal stability was drastically reduced and the decomposition started between 65 and 80°C. This allowed the lithographic imaging of these polymers in the presence of a photochemical acid generator. In addition, the imaging of these polymers by UV light in the absence of acid was possible, due to the moderate photolability of the azo group.