Synthesis of soluble polyimides for vertical alignment of liquid crystal via one-step method

A series of polyimides (PIs) were copolymerized from 4-dodecyloxy-biphenyl-3′,5′-diaminobenzoate (DBPDA), 3,3′-dimethyl-4,4′-methylene-dianiline (DMMDA) and 4,4′-oxydi(phthalic anhydride) (ODPA) via one-step method. The PIs possessed excellent solubility in polar aprotic solvents and easily formed thin flexible films by solution casting. The glass-transition temperatures (T_gs) of the PIs were in the range of 219-242 °C and thermal decomposition temperatures in nitrogen occurred above 350 °C. The resultant PI films exhibited high transparency at wavelengths greater than 400 nm and induced excellent uniform vertical alignment of liquid crystal (LC). Even after the rubbing process, the pretilt angles of LC were still above 89°. The PI seems to be a prospective material for alignment layers in flexible displays.