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To date, an inconclusive and partially contradictive picture exists on the behavior of neutral Ni(II) insertion polymerization catalysts toward methyl methacrylate (MMA). We shed light on this issue by a combination of comprehensive mechanistic NMR and EPR studies, isolation of a key Ni(I) intermediate, and pressure reactor studies with ethylene and MMA, followed by detailed polymer analysis. An interlocking mechanistic picture of an insertion and a free radical polymerization is revealed. Both polymerizations run simultaneously (25 bar ethylene, neat MMA, 70 °C); however, the chain growth cycles are independent of each other, and therefore exclusively a physical mixture of homo-PE and homo-PMMA is obtained. A Ni-C bond cleavage was excluded as a free radical source. Rather a homolytic P-C bond cleavage in the labile aryl phosphine ligand and the reaction of low-valent Ni(0/I) species with specific iodo substituted N^O (Ar-I) ligands were shown to initiate radical MMA polymerizations. Several reductive elimination decomposition pathways of catalyst precursor or active intermediates were shown to form low-valent Ni species. One of those pathways is a bimolecular reductive coupling via intermediate (N^O)Ni(I) formation. These intermediate Ni(I) species can be prevented from ultimate decomposition by capturing with organic radical sources, forming insertion polymerization active [(N^O)Ni(II)-R] species and prolonging the ethylene polymerization activity.

Selective catalytic carbonylation of the trisubstituted double bond of citronellic acid is enabled via an isomerization–functionalization approach. Alkoxycarbonylation with [{1,2-(tBu2PCH2)2C6H4}Pd(OTf)2] as a catalyst precursor occurs with >97% selectivity for the terminal diester dimethyl-3,7-dimethylnonane-dioate. This prevails much over the typical cationic methoxyaddition. The reactive primary carboxy group formed allows for e.g. the preparation of the high molecular weight novel polyester poly[3,7-dimethylnonanediyl-3,7-dimethylnonanedioate].

Catalytic emulsion polymerization of ethylene with nickel catalysts in the presence of silica nanoparticles affords stable dispersions of silica/polyethylene nanocomposite particles. The modification of the surface of silica particles by grafting upon their surface of octenyl- or octylsilanes is a prerequisite for obtaining composites. Different morphologies of composites particles were observed depending on the microstructure and crystallinity of the polyethylene part, controlled by different catalyst precursors. Composite structures consisting of silica spheres at the surface of lentil-like crystalline polyethylene particles were formed with a nickel(II) phosphinoenolate catalyst precursor or with the Ni(II) salicylaldiminato complex [{k2-N,O-6-C(H)=NAr-2,4-I2C6H2O}NiMe(tmeda)] (Ar=2,6-{3,5-(F3C)2C6H3}2C6H3). In contrast, silica particles homogeneously embedded in an amorphous polyethylene matrix are observed by TEM when another Ni(II) salicylaldiminato catalyst precursor (Ar = 2,6-{3,5-Me2C6H3}2C6H3) was used in the presence of a copolymerizable octenyl-modified silica.

The preparation of aqueous dispersions of very small particles (size < 30 nm) of various polymers (polyethylenes, stereoregular 1,2-polybutadiene, and polyalkenamers) by catalytic polymerization with a water-soluble catalyst, or with microemulsions of lipophilic catalysts is reviewed.

Very small polymer particles of 10-30 nm size with various microstructures (polyethylene, syndiotactic 1,2-polybutadiene, poly(cycloolefins)) are prepared by catalytic polymerization with aqueous catalyst microemulsion.

Emulsion polymerization is among the most important polymerization processes. As a product, polymer latices that are stable colloidal aqueous dispersions of polymer particles of about 50 nm to 1 mm in size are obtained. About ten million tons annually of polymer latices are used for a variety of applications, such as environmentally friendly coatings and paints. To date, polymer latices are produced industrially by freeradical polymerization exclusively. Styrene–butadiene copolymers, acrylate homoand copolymers, and vinyl acetate polymers are the major industrial products. 2] The range of polymer microstructures accessible by free-radical polymerization and corresponding materials properties is limited. For example, the synthesis of dispersions of saturated inert polymers, which do not bear hydrolyzable groups is a challenge. It is desirable to synthesize dispersions from simple olefins obtained directly from cracking of hydrocarbon feedstocks. This process would avoid the need to convert the cracked products to monomers such as acrylates or vinyl esters, which consumes energy and raw materials. We and the group of Claverie have recently reported the synthesis and properties of polyethylene dispersions by catalytic polymerization in emulsion. For traditional free-radical polymerization, the synthesis of very small particles is the subject of increasingly intense effort. 8] Microemulsion polymerization is a particularly suitable, albeit special, technique. Latices of, for example, polystyrene particles as small as 10 nm diameter have been prepared by microemulsion polymerization. A strong limitation is that microemulsions only form under specific

International audience; Ring opening metathesis polymerization of the natural sesquiterpenes caryophyllene and humulene, optionally complemented by exhaustive post-polymerization hydrogenation, yields non-crosslinked linear polymers with unprecedented microstructures reflecting the specific scaffolds of the feedstocks and with low glass transition temperatures in the range from -15 to -50 degrees C.