Polyurethane polymers (PUs) have been synthesized as solid-solid phase change materials for thermal energy storage using three different kinds of diisocyanate molecules and polyethylene glycols (PEGs) at three different molecular weights. PEGs and their derivatives are usually used as phase change units in polymeric solid-solid phase change materials due to the hydroxyl functional groups. 1000, 6000, and 10,000 g/mol number average molecular weight PEGs are used as working element as hexamethylene, isophorone, and toluene diisocyanates are used as hard segment at the backbone. The effects of molecular weight of PEG and type of diisocyanate on the thermal energy storage properties have been discussed. Only two of the produced polymers show solid-liquid phase change as the rest show solid-solid phase transitions. The produced PUs with a solid-solid phase transitions have potential to be used in thermal energy storage systems. (C) 2012 Elsevier Ltd. All rights reserved.