Coordination polymerization of ethylene in water by Pd(ii) and Ni(ii) catalysts

Abstract

Ethylene is polymerized in water as a reaction medium by Pd(II) and Ni(II) complexes to afford branched or linear homopolymer.Water possesses unique properties as a reaction medium. It is highly polar and immiscible with most organic compounds, has a high heat capacity and also features a strong propensity for micelle formation. In addition, water is an ideal medium from an environmental and safety perspective. Thus, emulsion and suspension polymerization of olefinic monomers is employed on a vast scale, e.g. for the direct production of water-based lattices, used for coatings and paints. In contrast to these free radical polymerizations, transition metal catalyzed coordination polymerization reactions in water have received less attention, as the early transition metal catalysts 1 used predominately are extremely sensitive to moisture.Late transition metal complexes are generally less sensitive to polar media due to their less oxophilic nature. Due to the propensity of late transition metal alkyl complexes for bhydride elimination, dimers or oligomers are usually obtained in C-C linkage of ethylene. 2 Only a limited number of catalysts for polymerization to high molecular weight products are known. Most of them are based either on neutral Ni(II) complexes 3,14a of formally monoanionic bidentate ligands or on cationic Fe, Co, Ni or Pd complexes 4 of neutral multidentate ligands with bulky substituted N donor atoms. 5 The aforementioned stability of late transition metal complexes is demonstrated by the tolerance of some of these polymerization catalysts towards polar functionalized comonomers 3d,4b,c and polar organic solvents. 3c,d,4c,6 In the context of possible side reactions in transition metal catalysis in aqueous media 7 (such as hydrolysis of metal alkyl species, attack of water on coordinated substrates or coordination of water to the metal center as a ligand), regarding polymerization reactions a conceivable effect of water on chain transfer 8 is of specific interest as small (absolute) changes in the overall chain transfer rate will strongly influence product molecular weight.A very slow (ca. 1 turnover per day) coordination polymerization of ethylene in water catalyzed by a Rh complex has previously been investigated. 9 We now report on the homopolymerization of ethylene in water by neutral Ni(II) and cationic Pd(II) complexes.

Z. Guan, Control of polymer topology through late‐transition‐metal catalysis, J Polym Sci Part A: Polym Chem (2003), 41(22), 3680–3692

“…88 metal systems: they are powerful in controlling the polymer topology 50 -57,83-88 and they have good functional group tolerance. 47,48,56,75,76 If the most striking feature of early-transition-metal olefin polymerization catalysts is their ability to control the stereochemistry of the polymerization of ␣-olefins, 91,92 the most powerful attribute of late-transition-metal polymerization catalysts must be their versatility for controlling the polymer topology (Scheme 10). 50 -57,83-88 We are currently focusing on the development of new catalysts, the synthesis of new functional materials, and the design of polymers with unconventional topologies by using late-transitionmetal catalysts.…”

“…47,48,75,76 By copolymerizing ethylene with functional monomers at different P E 's, we have obtained copolymers carrying a variety of functional groups with tunable topologies (Scheme 5). 56 This offers a simple one-pot approach to the design of functional polymers with a broad range of topologies.…”

Aqueous Dispersions of Nonspherical Polyethylene Nanoparticles from Free‐Radical Polymerization under Mild Conditions

“…The VOC issue has been largely solved for lowpressure catalytic Ziegler-Natta polymerizations by using solvent-free gas-phase processes. For slurry polymerization, new catalysts compatible with "green" diluents such as supercritical CO 2 [6,7] or water [8][9][10][11] have been developed. Recently we successfully produced polyethylene (PE) by a radical pathway under less energy-consuming conditions: medium pressure below 250 bar and a low temperature of 70 8C using organic solvents (toluene or THF).…”

Polymer dispersions from catalytic polymerization in aqueous systems

“…Two specific types of catalyst system have emerged for ethylene polymerization in aqueous systems, nickel(II)phosphinoenolato complexes [42][43][44][45][46][47] (1) and nickel(II) salicylaldiminato complexes 44,[48][49][50][51] (2). Both types of catalysts had originally been developed for non-aqueous polymerizations.…”