We investigate the effects of polymer volume fraction on the mechanical properties of polymer gels by varying the volume fraction of network at preparation (φ0) and at interested state (φm). Furthermore, we investigate the effect of φ0 on the degree of the equilibrium swelling. We employ the Tetra-PEG gels with precisely tuning network strand length and the polymer volume fraction at preparation (φ0) as a model system. The φ0-dependence of the elastic modulus is almost proportional to φ0/N, which corresponds to the prediction of the classical rubber elasticity theory. The φm-dependence of the elastic modulus exhibits the crossover at φ*. The dependence in semi-dilute region is stronger than that in dilute regions. The φ0-dependences of the elastic modulus and the polymer volume fraction at the equilibrium swollen state also exhibit the crossover at φ*. The dependences in semi-dilute region are weaker than those in dilute regions. The Obukhov model successfully describes these dependences by considering the excluded volume effect. On the other hand, the familiar C* theorem fails to explain the experimental results.
