Preparation of 1,2,3,4- cyclobutanetetracarboxylic acid dianhydride (CBDA)To a 2L quartz glass photoreactor equipped with sixteen UV lamps (300nm) , a stirrer and a cooler were attached and 250ml of ethyl acetate and 100g of maleic anhydride were added thereto followed by stirring for complete mixing. To avoid an excessive temperature increase, an air-cooling type cooler was first run and then UV light was illuminated for a photoreaction for 24h with stirring so as not to have the reactants adhered to the reactor walls. As a result, 71g of white solid was obtained. After the filtration, the white solid was dried for 24h in a vacuum dryer at 60°C Thus-obtained solid was then added to acetic anhydride, dissolved therein and slowly heated to 150°C followed by the reaction for 24h . Hot reaction solution was filtered through a filter paper to remove impurities and kept in a freezer at the temperature of 0°C or less for recrystallization for 24h to obtain a yellow solid. Thus-obtained solid was filtered and washed three times with 1,4-dioxane to remove acetic anhydride, and then dried in a vacuum oven at 60°C for 48h to obtain 64g of 1, 2, 3, 4 -cyclobutane tetracarboxylic acid dianhydride (CBDA) .
