Polyisocyanotripeptides (TriPIC) are biomimetic polymers which consist of a β-helical backbone stabilized by hydrogen bonds between amide groups. Their oligoethylene glycol side chains give aqueous TriPIC solutions a thermoresponsive behavior: at 50 °C the solution becomes a hydrogel. In this paper we study the molecular structure and water dynamics of TriPIC aqueous solutions while undergoing gelation using FT-IR spectroscopy and polarization-resolved femtosecond infrared spectroscopy (fs-IR). We find evidence that the oligoethylene glycol side chains trap part of the water molecules upon gel formation, and we propose that the interaction between the oligoethylene glycol side chains and water plays an essential role in the bundling of the polymers and thus in the formation of a hydrogel.