Polymerization of benzoguanamine (BGA) and 2,4-tolylenediisocyanate (TDI), BGA-TDI polycondensation polyurea (PU), and pyromellitic dianhydride (PMDA) in solid phase under microwave radiation was studied. In the system of TDI and BGA, the effect of microwave radiation time, the composition and concentration of monomer, the temperature, and the concentration of catalyst on the third-order optical nonlinearities of polymer were discussed. In the system of PU and PMDA, the effect of imidization degree on third-order optical nonlinearities was also discussed. The results showed that the prepared polymer had high third-order nonlinear optical coefficients (PU: chi((3)) = 1.174 X 10(-13) esu) and fast time responses (24 ps); simultaneously, the third-order optical nonlinearities of polymer were improved greatly by microwave radiation. The results also showed that third-order optical nonlinearities were affected not only by the length of the polycondensate chain but also by the molecular structure, which was explained and confirmed by the computation of the AMI semiempirical method and UV-visible absorption spectrum. (C) 2003 Wiley Periodicals, Inc.