Solid-solid phase change materials (SS-PCMs) are very promising in thermal management due to controlling temperature by storing and releasing heat, negligible volume expansion during phase transition and no leakage issue. We have synthesized and characterized a crosslinking co-polymer Polyethylene glycol (PEG)/toluene diisocyanate (TDI)/ polystyrene co-allyl alcohol (PSAA). We have shown two different forms of the same polymer by drying it with two different solvents: water and acetone. A comparative study is performed to obtain insights into the synthesis process of the SS-PCM. The polymers, derived from the two different processes, have the same chemical structure, and crystalline phases; however, they have different thermophysical properties and morphologies. The true density of polymer dried in water and acetone is 1.62 g/cc and 1.29 g/cc, respectively. The corresponding decomposition temperature is 371 °C and 402 °C. Polymer dried in water absorbs 100.24 J/g during heating and releases 96.282 J/g during cooling, compared to corresponding values of 129.9 J/g and 127.5 J/g for polymer dried in acetone. Both forms of the polymer are promising as SS-PCM material, which can be used to cool electronic devices in various applications. It is found that the heat sink with 5 plate fins filled with polymer dried in water significantly reduced the chip temperature with earlier initiation of phase transition compared to the heat sink containing only PCM.