Summary
The history of exploration of ideal polymer networks is reviewed, followed by a demonstration of fabrication and applications of novel polymer networks free from defects/entanglements. The networks, we call, are Tetra‐PEG gels, consisting of two types of tetra‐arm poly(ethylene glycol) (PEG) prepolymers that have mutually reactive amine (Tetra‐PEG‐NH2) and activated ester (Tetra‐PEG‐NHS) terminal groups, respectively. Here NHS represents N‐hydroxysuccinimide. The novelty lies in “cross‐end‐coupling” of symmetrical tetra‐arm PEGs having complementary end groups. Small‐angle neutron scattering (SANS) results on Tetra‐PEG gels, together with mechanical properties and swelling behaviors, strongly suggest that thus prepared Tetra‐PEG gels are near‐“ideal” polymer networks with very small fractions of defects. In order to answer the reasons why such a structure could be formed, the kinetics of gelation was investigated by IR, UV, and time‐resolved rheological and SANS measurements. Furthermore, fabrication of Tetra‐PEG ion gels, having good mechanical properties, is demonstrated.