Syntheses and Properties of Soluble Biphenyl-Based Polyimides from Asymmetric Bis(Chlorophthalimide)s

A novel synthesis of asymmetric bis(chlorophthalimide)s (3,4-BCPIs) has been established. The polymerizations of them produced higher molecular weight (0.38-0.51 dL/g) polyimides containing biphenyl units than those of isomeric polymers derived from symmetric bis(chlorophthalimide)s (4,4′-BCPIs) and 3,3'-BCPIs. The distribution of the formed biphenyl units of head to tail, head to head, and tail to tail in the chain of the polymers was about 58.0:21.0:21.0, determined by ¹³C NMR spectra of the polymers. The composition of model compounds, determined by HPLC, was well consistent with the ¹³C NMR spectrum result. Comparing with polymers derived from 4,4?′-BCPIs and 3,3′-BCPIs, the polymers derived from 3,4-BCPIs showed better solubilities in N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and N-methylpyrrolinone (NMP). Flexible films could be cast from the polymer solution with the inherent viscosities of above 0.35 dL/g. The polymer derived from asymmetric bis(chlorophthimide)s gave the highest T_g among the isomeric polymers. The 10% weight loss of these polyimides was above 549°C.