Synthesis and functionalization of ROMP-based gradient copolymers of 5-substituted norbornenes

Gradient copolymers of exo-5-(benzyloxy)norbornene and exo-5-[(4-tert-butyl)benzyloxy]-norbornene were synthesized via ring-opening metathesis polymerization (ROMP). Kinetic studies revealed that the reactivity ratios of both monomers were close to unity. As predicted, this monomer pair did not result in copolymers with significant gradients under batch polymerization conditions. However, semibatch conditions resulted in copolymers with sizable gradients whose shape was independent of the rate of addition. Addition of the monomers simultaneously via a dual and opposite ramping strategy led to a 50/50 copolymer with an exceptionally linear g adient. These gradient copolymers were further functionalized via hydrogenation, bromination, and bromoalkoxylation.