This paper reviewed the concept of chaim entanglement and the methods to characterize entanglement.A new 1H-NMR strategy was developed to characterize the degree of chain interpenetration in glassy polymers chain

which indirectly offer the information of entanglement.This strategy was run in the isotopically enriched polymer blends using dipolar filter under fast magic angle spinning.By this strategy we found the original degree of interpenetration of polymer chains in solution could be partly retained by freeze drying.It was also found that in the PS cast film

even when the molecular weight of PS was much less than its critical entanglement molecular weight(M_c)

the PS chains interpenetrated heavily

in which Van der Waals interaction played an important role.