13 C-NMR analysis of chain microstructure of copolyimides on the basis of 2,2-bis[(3,4-dicarboxyphenoxyl)-phenyl]-propane dianhydride synthesized in molten benzoic acid

Three series of copolyimides CPI-1, CPI-2 and CPI-3 were prepared in molten benzoic acid, based on 2,2-bis-[(3,4-dicarboxyphenoxy)-phenyl]-propane dianhydride (intermonomer) and three pairs of diamines (comonomers): aromatic/aliphatic (CPI-1, CPI-3) and moderate basic aromatic/low basic aromatic (CPI-2). The chain microstructure of copolyimides was determined by means of the high resolution ¹³C NMR spectroscopy. It was found that microstructure of copolyimides depends on the order of comonomers/inermonomer loading. The one-shot loading of comonomers/intermonomer mixture leads to random copolymer whereas slow addition of intermonomer to the mixture of two comonomers leads to preferentially multi-block copolymer.