Water-soluble single-component (kappa2-N,O)-salicylaldiminato nickel-methyl complexes 1-4-L (L = TPPTS, TPPDS, H2N-PEG-OMe) allow for the catalytic polymerization of ethylene under organic solvent-free aqueous conditions producing high molecular weight polyethylene with particle sizes below 10 nm. Amphiphilic TPPDS- and H2N-PEG-OMe complexes exhibit a polymerization activity in water higher than that in toluene. A solvation-favored activation of precatalysts 1-4-L by equilibrium dissociation of L in aqueous solution likely accounts for this enhanced polymerization activity. The observed generation of a given particle by a single active site is an unprecedented mechanism for formation of aqueous particle dispersions.

Neutral (salicylaldiminato)nickel(II) methyl complexes [{6-C(H)dNAr-2,4-I 2 C 6 H 2 O-κ 2 N,O}NiMe(L)] (Ar ) 2,6-{3,5-(F 3 C) 2 C 6 H 3 } 2 C 6 H 3 ) with different water-soluble ligands L (2a, L ) 1,3,5-triaza-7-phosphaadamantane; 2b, L ) hexamethylenetetramine (urotropine); 2c, L ) tetraethylammonium pyridine-3-sulfonate; 2d, L ) amino-terminated poly(ethylene glycol) monomethoxy ether) were prepared. 2a-d are potentially water-soluble catalyst precursors for ethylene polymerization, which form a water-insoluble active site [{κ 2 -N,O}NiR(ethylene)] (R ) growing chain). Only complex 2d was found to be watersoluble (>2 mmol L -1 ); 2c is soluble in water/2-propanol mixtures. In toluene as a reaction medium, only the relatively weakly coordinated tertiary amine complex 2b is polymerization active (1.7 × 10 4 TO). In aqueous systems 2c,d are also active due to compartmentalization of the active site in the polymer particles and of L in the aqueous phase. Polyethylene particle sizes vary from 18 nm (dispersions formed with 2d) to over 0.5 µm (2c) to suspensions (2b) depending on the initial state of the reaction mixture, correlated with catalyst solubility.

Syndiotactic 1,2-polybutadiene nanoparticles (volume average diameter 13 nm) were functionalized in aqueous dispersion by free radical mercaptan addition. By appropriate choice of both watersoluble radical initiator and mercaptan concentration, nanoparticles with a degree of functionalization of up to 85% were prepared using 3-mercaptopropionic acid methyl ester and 3-mercaptopropionic acid. Only a minor portion of double bonds formed cycles instead of the desired thiol-ene addition products. The composition and structure of the nanoparticles were elucidated by combination of elemental analysis, NMR, IR, DLS, and TEM. Highly hydrophilic mercaptans (3-mercaptopropanesulfonic acid sodium salts), in contrast, only reacted with surface accessible double bonds to afford stable and redispersible nanoparticles solely stabilized with covalently bound moieties on their surface. Analogous grafting of the tripeptide glutathione was demonstrated.

No abstract

(1) (BHT ) 3,5-di-tert-butyl-4-hydroxytoluene). Cispolybutadiene is formed in nonaqueous solution polymerization. The presence of water decreases activity and polymer molecular weight and increases trans incorporation of butadiene units. In emulsion polymerization, stable polymer dispersions can be obtained with complex 2 and 3, respectively. The microstructure is strongly altered by comparison to nonaqueous polymerization. Trans-polybutadiene is formed with activities of up to 1.5 × 10 3 mol (butadiene) mol (Ni) -1 h -1 . The semicrystalline latex particles have sizes of ca. 200 nm, with a monoclinic structure.