Kinetic Study of the Ring-Opening Metathesis Copolymerization of Ionic with Nonionic Cyclooctatetraene Derivatives To Yield Polyacetylene Ionomers

Abstract

The ion density in ionically functionalized polyacetylenes can be controlled by the ring-opening metathesis copolymerization of functionalized cyclooctatetraene (RCOT) monomers. Studies are reported on the kinetics for copolymerization of anionic (M_A, R = −CH₂CH₂SO₃⁻NMe₄⁺ ) and cationic (M_C, R = −CH₂CH₂NMe₃⁺CF₃SO₃⁻) RCOTs with a nonionizable RCOT (M_T, R = −SiMe₃) initiated by the well-defined tungsten imidoalkylidene catalyst W(CH(o-C₆H₄OMe))(NC₆H₅)(OCCH₃(CF₃)₂)₂(THF). Twenty separate copolymerizations were studied as a function of the mole fraction of ionic monomer in the feedstock. The monomer consumption was observed to follow zero-order behavior over a range of monomer concentration in the M_A−M_T system, whereas it was observed to follow first-order behavior in the M_C−M_T system. The zero-order behavior in the M_A−M_T system was observed to lead to much less drift in polymer composition than predicted by classic copolymerization theory. The initial rates of monomer conversion were determined and used to calculate the copolymer composition curve. The curves exhibited sigmoidal shapes as described by reactivity ratios r_C = 8 ± 3 and r_T = 4 ± 2 for the M_C−M_T system and r_A = 2.0 ± 0.3 and r_T = 2.3 ± 0.3 for the M_A−M_T system. In all cases, the rate of initiation was observed to be slow relative to propagation, and the initiation rate for M_T was observed to be approximately a factor of 4 greater than for the ionic monomers under similar conditions of monomer and catalyst concentration. The observed trends are explained in terms of ion−ion interactions. These interactions are argued to create different local activities of the ionic monomers in the vicinity of an active catalyst center with ultimate ionic monomer as compared to near either the uninitiated catalyst or an active catalyst center with ultimate nonionic monomer. The largest effects are observed in the M_C−M_T system where, in addition to the largest reactivity ratios, the ratio of the overall polymerization rate to the initiation rate increases by a factor of 20 in progressing from the homopolymerization of M_T to that of M_C.