Ultra-high-Tg chromophoric polyimides and polyureas as high-performance nonlinear optical materials

Three approaches to the construction of high-Tg polyimides and polyureas as second-order NLO materials are discussed. In the first approach, copolymerization of bismaleimides with o,o′-diallylbisphenol-A followed by functionalization with high-β NLO chromophores using a Mitsunobu procedure yields, after poling and curing, a series of heavily crosslinked chromophoric polyimides with Tg values as high as 320°C and partially resonant X⁽²⁾ responses as high as 1.0×10^-7 esu (42 pm/V at 1064 nm, 1.17 eV). In the second two approaches, copolymerization of the chromophore 4,5-bis(4′-aminophenyl)-2-(4″-nitrophenyl)imidazole with bismaleimides or diisocyanates yields polyimides and polyureas with Tg values as high as 292°C and partially resonant X⁽²⁾ values as high as 0.62×10^-7 esu(25 pm/V at 1064 nm). It is found that careful attention to the details of curing and crosslinking during poling results in NLO-active matrices exhibiting negligible decay in X⁽²⁾ on aging in air at 100°C for periods of 1,000-4,000 h. The imidazole based materials exhibit only about 10% X⁽²⁾ decay on aging for 100 h at 200°C under N₂.