Schiff bases of types 1, 2, and 3, easily prepared by the condensation of primary amines with pyridine-2-carboxaldehyde, glyoxal, or 2-acetylpyridine, respectively, are described as ligands for a copper(I) catalyst in the atom transfer polymerization of a range of methacrylates in toluene and xylene solution. Increasing the length of the alkyl group on ligands of type 1 increases the solubility of the catalyst in nonpolar solvents. The rate of polymerization increases on going from R = ethyl to propyl; however, on increasing the length of R further, we see no effect on the rate. The molecular weight distribution is narrow for all ligands where R = n-alkyl, and the number-average molecular weight (M n) increases linearly with conversion. A decrease in rate and a loss of control are observed when branching is introduced in the α-position of the side chain. The polymerization is approximately first order in initiator, 0.90 ± 0.22, CuBr, 0.90 ± 0.13, and methyl methacrylate, 0.93 ± 0.01. Polymerization with CuBr in conjunction with diazabutadiene ligands does not proceed very effectively, due to the high stability of the copper(I) complexes with regard to oxidation. The mechanism of the reaction is complex and may differ on subtle changes in ligand, metal, solvent, etc. The ligand systems presented in this paper offer a wide range of versatility when choosing the most effective system for a particular application. The Schiff base ligands, when used as described, provide an excellent method for achieving the controlled polymerization of a wide range of methacrylates at relatively mild temperatures in hydrocarbon, noncoordinating, solvents.

This paper demonstrates that atom transfer polymerization of methyl methacrylate mediated by CuBr/N-alkyl-2-pyridylmethanimine complexes in toluene proceeds effectively at temperatures as low as 15°C, while maintaining control over molecular weights and yielding narrow polydispersity indexes. The reaction can even be performed at -15°C with a number average molecular weight, M n, of 6980 and a polydispersity, PDI, of 1.28 being achieved in 116 h; however, the molecular weight control is less effective. The polymerizations were performed at 90, 60, 40, and 15°C with the first-order rate plots, molecular weight vs conversion plots, and final polydispersity indexes consistent with little or no terminationsliving/controlled polymerization. Methyl hydroquinone (MeHQ) has been demonstrated to accelerate the polymerization by a factor of 3-4 at temperatures below 40°C. An activation energy, Ea, for polymerization in the absence of phenol was determined to be 60.3 kJ‚mol -1 and is significantly reduced to 44.9 kJ‚mol -1 in the presence of MeHQ. These results suggest that coordinating phenols modify the active polymerization center. The stereochemistry of the polymers produced are consistent with that observed for conventional free-radical polymerization in that the fraction of syndiotactic arrangements increases as the reaction temperature is lowered. At 90°C, 59.1% rr triads are obtained with a persistence ratio of 0.924 and at -15°C, 71.5% rr triads are obtained.

Water-insoluble organic compounds are often used in aqueous environments in various pharmaceutical and consumer products. To overcome insolubility, the particles are dispersed in a medium during product formation, but large particles that are formed may affect product performance and safety. Many techniques have been used to produce nanodispersions-dispersions with nanometre-scale dimensions-that have properties similar to solutions. However, making nanodispersions requires complex processing, and it is difficult to achieve stability over long periods. Here we report a generic method for producing organic nanoparticles with a combination of modified emulsion-templating and freeze-drying. The dry powder composites formed using this method are highly porous, stable and form nanodispersions upon simple addition of water. Aqueous nanodispersions of Triclosan (a commercial antimicrobial agent) produced with this approach show greater activity than organic/aqueous solutions of Triclosan.

In this paper we report a comparative experimental thermochemical and ab initio quantum chemical study of metal−ligand bonding and bonding energetics in the group 3, lanthanide, group 4, and group 5 zerovalent bis(arene) sandwich complexes Sc(TTB)2 (1) Y(TTB)2 (2), Gd(TTB)2 (3), Dy(TTB)2 (4), Ho(TTB)2 (5), Er(TTB)2 (6), Lu(TTB)2 (7), Ti(TTB)2 (8), Zr(TTB)2 (9), Hf(TTB)2 (10), Ti(toluene)2 (11), and Nb(mesitylene)2 (12) (TTB = η6-(1,3,5-tBu)3C6H3). Derived D̄(M−arene) values by iodinolytic batch titration calorimetry in toluene for the process M(arene)2(solution) → M° + 2arene(solution) are rather large (kcal/mol):  45(3) (1), 72(2) (2), 68(2) (3), 47(2) (4), 56(2) (5), 57(2) (6), 62(2) (7), 49(1) (8), 55(2) (11), 64(3) (9), 67(4) (10), and 73(3) (12). Ab initio relativistic core potential calculations on M(C6H6)2, M = Ti, Zr, Hf, Cr, Mo, W, reveal that the metal−ligand bonding is dominated by strong (greater in group 4 than in the group 6 congeners) δ back-bonding from filled metal d x y and d x 2 -y 2 orbitals to unoccupied arene π orbitals, which decreases in the order Hf > Zr > Ti > W > Mo > Cr. Calculated geometries and D̄(M−C6H6) values (at the MP2 level) yield parameters in favorable agreement with experiment. The latter analyses evidence a great sensitivity to electron correlation effects. Marked, group-centered dependences of the measured D̄(M−arene) values on the sublimation enthalpies of the corresponding bulk metals, on the metal atomic volumes, and, for the lanthanides and Y, on the corresponding free atom f → d promotion energies are also evident.