Polymerization of benzoguanamine and pyromellitic dianhydride under microwave radiation and its third-order optical nonlinearities

Polycondensation and imidization of benzoguanamine and pyromellitic dianhyd ride under microwave radiation were studied. The effects of the microwave r adiation time (power), the composition of the monomer on the imidization, a nd the polymer yield were discussed. The polycondensates' third-order optic al nonlinearities and time responses were measured by a phase conjugate for ward, 3-dimensional degenerate, four-wave mixing technique. At the same tim e they were compared with relevant conventional thermopolymerization. The r esults showed that the polycondensates had high third-order nonlinear optic al coefficients [polyimide (PI) chi ((3)) = 1.181 x 10(-13) esu] and fast t ime responses (22 ps). The third-order nonlinear optical coefficients under microwave radiation were higher than that of conventional thermopolymeriza tion (microwave radiation PI chi ((3)) = 1.181 X 10(-13) esu: thermopolymer ization PI chi ((3)) = 0.686 X 10(-13) esu). The experimental results also showed that the third-order optical nonlinearities were not only affected b y the length of the polycondensate chain, but also the polycondensate pi -e lectron density distribution, which was explained and confirmed by computat ion with the semiempirical Austin method. (C) 2001 John Wiley & Sons, Inc.