Chain microstructure of soluble copolyimides containing moieties of aliphatic and aromatic diamines and aromatic dianhydrides prepared in molten benzoic acid

Abstract

Two series of high-molecular-weight copolyimides CPI-1 and CPI-2 containing five-membered imide cycles have been prepared by high-temperature polycondensation in molten benzoic acid (BA) at 140°C from a pair of aromatic/aliphatic diamines (9,9-bis(4-amino)fluorene (AFL) and 1,12-dodecamethylene diamine (DDA)) and one dianhydride (4,4′-oxydiphthalic anhydride (in CPI-1 series) or (1,3-phenylene)-bis(4-oxyphtalic anhydride) (in CPI-2 series)) using different order of the components loading. The diamines moiety distribution in chain was analyzed by means of high resolution carbon nuclear magnetic resonance. It is found that CPI-1 and CPI-2 samples prepared using one-shot comonomers/intermonomer loading have random moieties distribution, whereas the samples prepared using stepwise addition of dianhydride to the mixture of two diamines have multiblock (MB) chain microstructure. Thus, despite complicated scheme of CPIs synthesis in molten BA including several reactions, the process as a whole displays a feature typical for ideal one-stage interbipolycondensation of symmetrical components with independent groups. The average block length increases when DDA and dianhydride are added together slowly to AFL solution in molten BA. The phase morphology of CPI-2 was studied by means of differential scanning calorimeter. The data obtained demonstrate symptoms of microphase separation in nascent powders of MB CPI-2.