The dynamics of rigid random polymer coils in dilute solution has been investigated by neutron spin-echo (NSE) spectroscopy. The polymers used were polynorbornenes that consist of chains of the bridged norbornene rings with hexyl (PNBH) or propyl (PNBP) side groups. These polymer molecules have large internal rotation barriers that hinder conformational changes and give each chain a kind of individual shape memory. Thereby the chains exhibit a dynamical stiffness that leads to a significantly retarded relaxation as compared to flexible polyisoprene chains (PI). While the latter perfectly match the prediction of the Zimm model, the polynorbornene spectra display the signature of a dynamical stiffness due to the "frozen" coil conformation of the PNBH or PNBP chains.