Force-extension relations for polymers with sliding links.

Topological entanglements in polymers are mimicked by sliding rings (slip links) that enforce pair contacts between monomers. We study the force-extension curve for linear polymers in which slip links create additional loops of variable sizes. For a single loop in a phantom chain, we obtain exact expressions for the average end-to-end separation. The linear response to a small force is related to the properties of the unstressed chain, while for a large force the polymer backbone can be treated as a sequence of Pincus-de Gennes blobs, the constraint effecting only a single blob. Generalizing this picture, scaling arguments are used to include self-avoiding effects.