Ruthenium catalysis in metathesis polymerization: Synthesis of linear copolymers of ethylene and polar vinyl monomers via metathesis

A comparison of the recently developed N-heterocyclic carbene (NHC)-ligated ruthenium benzylidene olefin metathesis catalyst (RuCl2(PCy 3)(1,3-dimesityl-4,5-dihydro-imidazol-2-ylidene)CHPh) and the analogous bis-phosphine benzylidene complex (RuCl2(PCy3) 2CHPh) in the context of acyclic diene metathesis (ADMET) polymerization was performed. The kinetic analysis revealed that at temperatures of 45--70°C the NHC complexes promote ADMET from two to six times faster than the bis-phosphine complex. A conspicuous induction period was witnessed for the NHC complex that was not present for the bis-phosphine complex. This behavior is a consequence of the much slower rate of the critical phosphine dissociation step for the NHC complex. Functionalized dienes polymerize at much slower rates than hydrocarbon dienes, although at high temperatures the difference in rate is not very significant.; Novel NHC-phosphine (RuCl2(PCy3)(1,3-dimesityl-4,5-dihydro-imidazol-2-ylidene)CHCH 3) and bis-pyridyl (RuCl2(3-bromopyridyl) 2(1,3-dimesityl-4,5-dihydro-imidazol-2-ylidene)CHCH3) ruthenium ethylidene catalysts were developed for the purpose of providing a methyl endgroup for ring-opening metathesis polymerization (ROMP) and characterized by a variety of methods including X-ray crystallography. The reactivity of these complexes in ROMP and cross-metathesis (CM) was investigated. The bis-pyridyl complex is capable of very controlled ROMP polymerization, which allows the synthesis of low polydispersity polyethylene with methyl endgroups via polymerization of cyclooctene followed by hydrogenation using the same catalyst.; The NHC ethylidene was used to synthesize copolymers of ethylene and polar vinyl monomers via ROMP copolymerization of cyclooctene and functionalized cyclooctenes followed by hydrogenation using the same catalyst. This convenient procedure allowed for the first time the synthesis of HDPE modified with between 2 and 6 mol% vinyl alcohol, vinyl acetate, methyl acrylate, t-butyl acrylate, and acrylic acid The crystalline structures for all of the polymers was shown to be that of orthorhombic polyethylene by infrared spectroscopy and wide-angle X-ray diffraction. The melting transitions of the polymers were in line with those expected for linear polyethylene with non-crystallizable defects. However, the linear ethylene-vinyl alcohol copolymers had melting transitions higher than the other copolymers at similar compositions, which indicates that the alcohol group is capable of crystallizing in the polyethylene lattice. These novel polymers were characterized by NMR and IR spectroscopies, DSC, TGA, DMTA, and WAXD.