Macrocycles 23. Odd–even effect in the cyclization of poly(ester imide)s derived from catechols

Various poly(ester imide)s, PEIs, were prepared from N-(4-carboxyphenyl) trimellitimide (4-CPTI) or from N-(3-carboxyphenyl) trimellitimide (3-CPTI). Various catechols or 5-methylresorcinol served as comonomers. MALDI-TOF mass spectrometry revealed that the PEIs derived from 4-CPTI and catechols contain significantly more even than odd cycles, whereas the PEIs derived from 3-CPTI and catechols contained almost equal amounts of odd and even-numbered cycles. The predominant formation of even-numbered cycles is explained by a ‘hair pin’ conformation of the growing oligomers based on strong donor–acceptor (DA) and dipole–dipole interactions. The resulting ‘collapsed cycles’ with parallel alignment of the 4-CPTI units have the consequence that most cyclic oligomers and polymers possess mesogenic properties and form a nematic melt. The temperature range of the nematic phase depends on the substituent of the catechol units.