In dilute heteropolymer solutions, a limited number of the chains, just like proteins, could collapse and associate to form a stable/metastable mesoglobular phase between single-chain globules and macroscopic precipitates. Recently, we found that inserting more hydrophobic comonomers into a thermally sensitive chain backbone surprisingly led to the formation of smaller mesoglobules in water. This apparent contradiction to our conventional wisdom can be satisfactorily explained in terms of the overlooked viscoelastic effect; namely, hydrophobic association inside each mesoglobule increases the chain relaxation time (tau(e)). When it becomes much longer than the interaction time (tau(e)) of two colliding mesoglobules, each mesoglobule behaves like a tiny nonadhesive "glass" ball. This stabilization mechanism is completely different from thermodynamic consideration in which one normally tries to make the particle surface hydrophilic so that tau(e) is reduced.