Exact Solution to Ideal Chain with Fixed Angular Momentum
  The statistical mechanics of a non-interacting polymer chain in the limit of a large number of monomers is considered when the total angular momentum, L, is fixed. The radius of gyration for a ring polymer in this situation is derived exactly in closed form by functional integration techniques. Even when L = 0 the radius of gyration differs from that of a random walk by a prefactor of order unity. The dependence on L is discussed qualitatively and the large L limit can be understood by physical arguments. 
J.M. Deutsch