and $\rho$ are observed in Fig. \[fig1\]b. Therefore, it can be concluded that the conformation changes of the polymeric chains control the glass transition temperature and the density. In fact, as the rigidity of the chain bending increases, the angle $\theta$ of the polymer chains tends to be stabilized at $\theta_0 = 109.5^\circ$ and the radius of inertia increases. As a result, the glass transition occurs at a higher temperature and the lower density (larger volume). At $\varepsilon_\mathrm{bend} \ls 1$, the effect of the bending interaction of Eq. (\[eq:bend\]) is weak compared to those of the LJ and FENE components of Eqs. (\[eq:LJ\]) and (\[eq:FENE\]). However, at $\varepsilon_\mathrm{bend} \gs 10^3$, the opposite phenomenon occurs.

It is noted that the glass transition occurs at a lower temperature for $L=3$ than for $L=50$, which is consistent with a previous report [@Durand_2010]. Correspondingly, the values of $\rho$ for $L=3$ becomes larger than that of $L=50$. However, common results were observed between $L=3$ and $50$ with respect to the dependences on the rigidity $\varepsilon_\mathrm{bend}$. Specifically, $T_g$ and $\rho$, as well as the conformation of the polymeric chains progressively change when the rigidity increases from $\varepsilon_\mathrm{bend} = 1$ to $10^3$, which also occurs for $L=50$.

