Two novel functional ladder-like polysilsesquioxanes with double-chain macromolecular backbones and nonlinear optical (NLO) chromophore-containing side chains for NLO applications (NLO-T-1 and NLO-T-2) were synthesized successfully for the first time via the introduction of the NLO chromophores to the side chains of the ladderlike polychloropropylsilsesquioxane (Cl-T-1) and ladderlike poly(4-chloromethylphenyl)ethylsilsesquioxane (Cl-T-2), respectively, by an etherification reaction. The obtained polymers were characterized by FTIR,H-1 NMR,C-13 NMR, Si-29 NMR, X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), vapour pressure osmometry (VPO), fluorescence spectroscopy and second-harmonic generation (SHG) measurements. The poled thin films of the above two ladder-like NLO polymers showed d(33) coefficients of 9.2 and 9.6 pm V-1, respectively. Compared with the corresponding single main chain polymers, the poled thin films of the synthesized ladder-like NLO polymers demonstrated a much higher thermal stability of SHG. (C) 2001 Elsevier Science B.V. All rights reserved.