Preparation and properties of the polyimide derived from cyclobutanetetracarboxylic dianhydride (CBDA) with diamines are investigated, focusing on the interfacial polycondensation of cyclobutanetetracarboxylic acid dimethylester dichloride (2a) with diamines.
Dimethylester was conveniently prepared from CBDA by refluxing in methanol solution. Dimethylester consists of two regio isomers; one is α-type (1a) with centrosymmetry, the other is β-type (1b) with plane symmetry. Separation of the mixture into each of pure 1a and 1b was successfully performed by fractional crystallization. The structure of the first fraction is 1a, which was determined by x-ray crystal analysis. The second fraction was necessarily assigned to 1b. 1a was converted into 2a by the reaction of thionyl chloride. The interfacial polycondensation of 2a with diamines afforded a high molecular weight polyamic ester. Polyimide was obtained only by heating the polyamic ester to about 230–280 °C. The cyclobutane polyimide thus obtained was thermally stable up to 400 °C, and less stable under hydrolysis than polypyromellitic imide.
