The polysilsesquioxane having amino and phenyl groups (APSQ) was prepared from the corresponding trimethoxysilanes by co-condensation under basic conditions. The amino group on APSQ was utilized as an initiator for graft polymerization of epsilon-caprolactone (CL). The ring-opening polymerization of CL, in the presence of a catalytic amount of the base prepared from triazabicyclodecene, proceeded effectively to afford the polysilsesquioxane having poly(CL) as the graft chains (GrPSQ). In the grafting, no formation of cross-linked product was observed. The grafted poly(CL) component in GrPSQ showed improved durability for heat as an advantage of the hybrid polymer containing polysiloxane structure. (C) 2008 Elsevier Ltd. All rights reserved.