Olefin cross-metathesis of polynorbornene with polypentenamer: New norbornene–cyclopentene multiblock copolymers

Abstract

Statistical multiblock copolymers of norbornene (NB) and cyclopentene (CP) with different compositions and average block lengths are synthesized via the metathesis of polynorbornene (PNB) with polypentenamer (PCP) mediated by Grubbs’ catalysts of the 1st (G1) and 2nd (G2) generations. Interest in the copolymerization of NB and CP is dictated by the attractive properties of their homopolymers, whereas its realization is hampered by the mismatch in their metathesis polymerization activities. This difficulty can be circumvented by starting from the homopolymers, which are well-known industrial products. Our study demonstrates that the interaction of PNB with PCP in dilute solutions at room temperature in the presence of G1 leads to the copolymers with short CP blocks of 1–3 units separating longer NB blocks. In situ 1H NMR monitoring of the process reveals nearly full depolymerization of PCP via the ring-closing intramolecular metathesis and the formation of NB–CP copolymers presumably via the interaction of CP with PNB. The depolymerization can be suppressed by increasing the concentration of reacting polymers and replacing G1 with more active G2. Under these conditions, the cross-metathesis of PNB with PCP results in the multiblock NB–CP copolymers with composition close to that of the initial homopolymer mixture, but short blocks of the both comonomers. A copolymer with longer blocks that can inherit properties of the parent homopolymers is obtained by decreasing the reaction temperature to 5 °C. Additional information about the structure of NB–CP copolymers is obtained via their hydrogenation followed by spectral and thermal characterization. Thus, the macromolecular cross-metathesis of unsaturated polymers appears to be a versatile method to synthesize copolymers with different backbone structures that are hard to reach by other methods.