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Macromolecules 9(3), 386–388. Publisher: doi.org/10.1021/ma60051a002

Institution-hosted author-paper reproduction: www.eng.uc.edu/~beaucag/Classes/Properties/Pincus76.pdf . The indexed abstract and section I on p. 386 identify the nonlinear restoring force for strongly elongated polymer chains in a good solvent.