= Polymer entanglement
A polymer entanglement is a constraint on a chain's motion caused by the inability of neighbouring chain contours to pass through one another. It is not a permanent chemical <cross-link>. In a dense <polymer melt>, these constraints can create long relaxation times and a transient <rubbery plateau>. Chains eventually release constraints through mechanisms such as <reptation> and motion of their neighbours. Entanglement therefore strongly affects dynamics even when the equilibrium size of a long chain remains approximately that of an <ideal chain> because excluded-volume interactions are screened.
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