A homologous series of PEG (various chain length)-substituted octasilsesquioxanes were prepared by the hydrosilylation of unsaturated PEGs (poly(ethylene glycol)s) with both octa(dimethylsiloxy)silsesquioxane (Q(8)M(8)(H)) and octahydridosilsesquioxane (T-8(H)). The silsesquioxane-PEGs materials were produced by the initial synthesis of a series of allyl-modified poly(ethylene glycol)s and subsequent attachment to both (Q(8)M(8)(H)) and (T-8(H)). The products were chemically characterized by Fourier transform infrared (FTIR) and nuclear magnetic resonance (H-1, C-13, and Si-29 NMR) spectroscopy, and the properties of the allyl PEGs and their POSS hybrids were thermally characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The attachment of the PEGs onto the POSS macromonomers (Q(8)M(8)(H) and T-8(H)) clearly demonstrated a chain-length-dependent increase in T-g and a concomitant suppression of crystallization.