Properties of ultrahigh-Tg chromophoric polyimides and polyureas as high-performance nonlinear optical materials: architecture-processing-temporal stability relationships

Three complementary approaches to the construction of electric field polable high-Tg (glass transition temperature) 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 approximately 260°C and χ⁽²⁾ responses as high as 1.0 × 10^-7 esu (42 pm/V at λ_o = 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 χ⁽²⁾ values as high as 0.62 × 10^-7 esu (25 pm/V at λ_o = 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 χ⁽²⁾ on aging in air at 100°C for periods of 1000 - 4000 h. The imidazole- based materials exhibit only approximately 10% χ⁽²⁾ decay on aging for 100 h at 200°C under N₂.