Relatively low thermal stability of second-order nonlinear optical (NLO) coefficient due to the relaxation of dipole orientation is a major problem limiting the practical application of these NLO polymers. NLO polymers with suitable T-g are always important for optical devices. In the present work a synthetic approach to styrene-(N-(4-hydroxyphenyl) maleimide) copolymer (SHMI) with 4-[N-ethyl-N-(2-hydroxyethyl) amino]-4'-nitroazobenzene (DR1) as side chain and chromophores has made it possible to efficiently prepare a NLO polymer. The copolymer with high T-g of 202 degrees C has low relaxation of dipole orientation. The maximum optical loss at the optical communication wavelength is less than 0.9 dB. NLO coefficient r(33) is 8.2 pm/V (1550 nm) and its maximum relaxation at room temperature is 18%. (c) 2008 Wiley Periodicals, Inc.