  We perform computer simulations of mechanically linked (poly[2]catenanes, PC)
and chemically bonded (bonded rings, BR) pairs of self-avoiding ring polymers
in steady shear. We find that BR's develop a novel motif, termed gradient
tumbling, rotating around the gradient axis. For the PC's the rings are
stretched and display another new pattern, termed slip-tumbling. The dynamics
of BR's is continuous and oscillatory, whereas that of PC's is intermittent
between slip-tumbling attempts. Our findings demonstrate the interplay between
topology and hydrodynamics in dilute solutions of connected polymers.
