Ruthenium mediated olefin metathesis: Materials with controlled microstructure and functionalization

Methylcyclopentene and cyclooctadiene were copolymerized via ring opening metathesis polymerization (ROMP) mediated by the well-defined complex (PCy ₃)₂Cl₂Ru = CHPh to produce materials with controlled microstructure and functionalization. The copolymer (COD/3-MCP) composition (10–80 methyls/1000 carbons) and melting point (T_m) (65–110°C) were controlled by comonomer feed ratio. Polymerizations performed in the presence of chain transfer agent (CTA) cis-2-butene-1,4-diacetate provided telechelic copolymers with controlled chain length (M_n 1500–3500 g/mol), and 13C NMR spectra were used to assign polymer microstructure. The ruthenium carbene was converted in situ to an active olefin hydrogenation catalyst. The effectiveness of this methodology depends on polymer microstructure, solvent, temperature, pressure and additives. Methylene chloride is the best solvent for hydrogenation (200°C, 800 psi H₂, Olefin/Ru ≈ 2000). The structure/property relationships of this family of materials was investigated by numerous methods. The number of backbone methyl branches had a significant effect on the melt transition temperature and enthalpy and zero shear viscosity. There was not a demonstrable effect on the energy of activation of flow. However, preliminary rheo-optical measurements indicate a strong dependence of the stress-optic coefficient on methyl branch.; The regiospecific and irreversible reaction of ruthenium carbenes (PR ₃)₂Cl₂RuCHR′ (R = PPh ₃ or PCy₃, R′ = Ph, CHCPh₂, (CH₂)₄CH₃ or polynorbornene) with electron rich vinyl ethers (EtOCH=CHR, R = H, CH₃, (CH₂) ₅CH₃, CH₂Ph or Ph) was also investigated. These reactions were monitored by 1H NMR spectroscopy and kinetic data was obtained under pseudo first order conditions ([vinyl ether] ₀/[Ru]₀ 10/1). The half lives (t_1/2) for this reaction were calculated from the observed kinetic data for [vinyl ether] = 0.15 M. 1H NMR data indicates that the observed metathesis was regiospecific and irreversible yielding a heteroatom stabilized alkylidene species (L_nRu=CHOEt). Ruthenium catalysts possessing electron rich alkyl phosphines were more reactive towards each subtrate. Coordination of heteroatom from the polymer backbone (poly(cyclobutene) with pendant amide or ether groups) significantly inhibited metathesis at all temperatures. The analogstripenylphosphine derivatives were less reactive and (PPh₃) ₂Cl₂RuCH(C₇H₁₀)_n reacts only with ethyl vinyl ether at 20°C. At 40°C methathesis was observed with other less hindered substrates.