Rubbery plateau ($G_R$)

The rubbery plateau is a frequency or time range in which a flexible polymer network has an approximately constant elastic storage modulus dominated by chain entropy. A permanently crosslinked elastomer retains a nonzero long-time modulus. An entangled uncrosslinked polymer melt can have a transient plateau but ultimately reaches terminal fluid flow at sufficiently low frequency. The plateau therefore must be interpreted with the network lifetime and observation window specified.