A series of POSS(PFG)n=2-6 macromonomers were further functionalized by reaction with methacryloyl chloride and then polymerized with methyl methacrylate to produce a series of hybrid materials where the amounts of POSS(PEG)n=2-6 used as cross-linkers varied from 0.1 to 0.5 mol %. Thermal investigations using TGA and DSC techniques revealed that both POSS concentrations and PEG chain length play important roles in defining structure-property relationships. Incorporation of POSS always increased thermal stability. Although the POSS is a bulky and multifunctional cross-linker, glass transitions did not always increase. In some instances bulkiness of the group created free volume and chain separation, which led to a reduction in the glass transition temperature.