Hydrogenated ring-opened polynorbornene: A highly crystalline atactic polymer

Ring-opening metathesis polymerization (ROMP) of norbornene with most catalysts produces a polymer with an atactic placement of the cyclopentylene rings, yet partial hydrogenation of this polymer is known to yield a crystalline product. We report here a facile catalytic route to saturate polynorbornene (PN); fully hydrogenated polynorbornene (hPN) is highly crystalline, with an equilibrium melting point estimated as 156°C. The crystal lattice is monoclinic, with parameters a = 6.936 Å, b = 9.596 Å, c = 12.420 Å, and β= 130.7° at room temperature, indicating nearly complete extension of the hPN backbone within the unit cell. The material remains highly crystalline until the melting point is reached, but near 105°C, the crystal structure transforms to one characterized by substantial rotational disorder of the hPN chains about their axes, while retaining substantial translational order.