<p>Polymer gel research has led to the development of hydrogels with a broad range of functions by tuning their molecular architecture, crosslinking reactions, and network structure. Within this landscape, poly(oligo (ethylene glycol) methacrylate) (pOEGMA)-based materials are useful polyethylene glycol (PEG) analogs. They are biocompatible, and their thermoresponsiveness can be tuned simply by changing the length of the ethylene oxide (EO) side chain. In this focus review, recent progress from our group is summarized to clarify how the EO side-chain length controls the formation, microstructure, and performance of pOEGMA gel networks. Side-chain-length effects on gelation conditions and mechanical properties are outlined, and thermoresponsiveness is subsequently linked by integrating dynamic light scattering with dynamic viscoelasticity. Small-angle neutron scattering provides direct evidence for composition- and temperature-dependent domain structures. Finally, nanoparticle diffusion, as a functional readout linking network heterogeneity to transport, including anomalous diffusion activation near the lower critical solution temperature, is discussed. These studies provide a multiscale framework for the rational design of pOEGMA-based hydrogels with controlled mechanics and transport.</p>