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 13 C NMR spectra of the polymers. The composition of model compounds, determined by HPLC, was well consistent with the 13 C 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.