Two luminescent block copolymers (PPVPEO200 and PPVPEO600), composed of poly(p-phenylene-vinylene) (PPV) segments with three phenylene vinylene units and poly(ethylene oxide) (PEO) segments with molecular weight of 200 and 600, respectively, have been successfully synthesized. The structures of the copolymers were verified using FTIR, H-1-NMR, and elemental analysis. Single-layer polymer light-emitting electrochemical cells (LEC) devices fabricated on the bases of thin films of PPVPEO600 and on the bases of thin films of blends of PPVPEO200 with additional PEO both demonstrated good electroluminescent (EL) performance with the onset voltage of 2.6 V and EL efficiency of 0.64 cd/A and 0.68 cd/A at 3.2 V, respectively. Thermal analysis shows that the decomposition temperature of PPVPEO600 is about 305 degrees C, which is higher than that of PPVPEO200 and PEO. AFM studies of PPVPEO600 thin films exhibits that the block copolymer self-assembles to form nanoscale network structures with pseudo-cross-linking points, thus accounting for its high thermal stability and good EL performance. (c) 2007 Wiley Periodicals, Inc.