Preparation of polymer colloids by chemical reactions in aerosols. I. Poly(p-tertiarybutylstyrene)

A procedure was developed by which polymer colloids can be prepared by polymerizing aerosol droplets of monomers with an initiator in the vapor state. This work describes the formation of poly(p-tertiarybutylstyrene) particles by exposing the corresponding monomer droplets to trifluoromethanesulfonic acid. It was found that the monomer-to-initiator mass ratio is the critical factor in determining the uniformity and morphology of the particles. Under ideal conditions spheres of narrow size distribution are obtained. Otherwise porous particles or soft particles with whiskers may develop. The aerosol was prepared in a falling film generator, but other procedures for producing monomer droplets may be used.     

Geranyl Acetate Emulsions: Surfactant Association Structures and Stability

The phase diagram of fragrance oil, geranyl acetate, water, and a surfactant, Laureth 4, was used to calculate the surfactant association structures present in emulsions with constant O/W ratio for increased fractions of surfactant. The liquid crystal appeared in the emulsion at a critical value of the surfactant fraction and additional surfactant caused an approximately linear increase of it, while the fraction of the aqueous phase experienced a corresponding reduction. The result of the calculations was confirmed by optical microscopy observation with the samples between crossed polarizers. The calculations revealed the formation of vesicles from the liquid crystal to result in a drastic reduction of the “free” aqueous phase, due to the amount of the aqueous liquid forming the core of the vesicle.     

Operator algebras and a theorem of Dieudonne

LetA be aC*-algebra with second dualA″. Let (φ _n)(n=1,...) be a sequence in the dual ofA such that limφ _n(a) exists for eacha εA. In general, this does not imply that limφ _n(x) exists for eachx εA″. But if limφ _n(p) exists whenever p is the range projection of a positive self-adjoint element of the unit ball ofA, then it is shown that limφ _n(x) does exist for eachx inA″. This is a non-commutative generalisation of a celebrated theorem of Dieudonné. A new proof of Dieudonné’s theorem, for positive measures, is given here. The proof of the main result makes use of Dieudonné’s original theorem.     

Nanoclusters in catalysis: a comparison of CS(2) catalyst poisoning of polyoxoanion- and tetrabutylammonium-stabilized 40 +/- 6 A Rh(0) nanoclusters to 5 Rh/Al(2)O(3), including an analysis of the literature related to the CS(2) to metal stoichiometry issue

It is crucial in metal particle catalysis to know the true number of catalytically active surface sites; without this knowledge it is impossible (i) to know the true turnover frequency (TOF, i.e., the moles of product/(moles of active metal atoms x time)); (ii) to know for certain whether a (quantitatively) better catalyst has been made-on a per-active-metal-atom basis; (iii) to know the amount of active sites remaining in a deactivated catalyst; and (iv) to know how many active sites have been regenerated in a reactivated catalyst. For this reason, herein we report the first quantitative, more complete and fundamental study of nanocluster catalyst poisoning using the preferred CS(2) method with polyoxoanion- and tetrabutylammonium-stabilized Rh(0) nanoclusters; 5% Rh/Al(2)O(3) is also examined as a valuable comparison point. Both catalysts are examined under essentially identical conditions and while catalyzing a prototype reaction, cyclohexene hydrogenation. A number of control studies are also reported to be sure that the kinetic method used to follow the CS(2) poisoned hydrogenation reaction is reliable, to test for H(2) gas-to-solution mass-transfer limitations, to test for reversibility in the CS(2) poisoning, and to test for loss of the volatile CS(2). The results allow 10 previously unavailable insights and conclusions, including the first quantitative comparison of the active-site corrected TOF for a nanocluster catalyst (in this case Rh(0) nanoclusters) to its supported heterogeneous counterpart (the 5% Rh(0) on Al(2)O(3)). The results show that the nanocluster surface Rh(0) is between 2.3 and 23 times more active on a per-active-metal-atom basis. Overall, the results introduce to the transition-metal nanocluster area the catalyst poisoning methodology necessary for the determination of the number of active metal sites. The important literature of CS(2) catalyst poisoning studies is also cited and discussed with a focus on the previously neglected issue of the exact poison/metal stoichiometry ratio. Significantly, the single metal crystal plus CS(2) literature provides evidence that the CS(2)/metal ratio probably lies between 1/1.5 and 1/10 in most cases. The data presented herein suggest that the CS(2)/Rh ratio for the Rh(0) nanoclusters is very likely within this range and for certain is <1/17.     

Detection and reactivity of Pd((C8H14)PCH2 CH2 P(C8H14))(CHPhCH2Ph)(H) as determined by parahydrogen-enhanced NMR spectroscopy

Pd(bcope)(OTf)2 (where bcope is (C8H14)PCH2CH2P(C8H14)) is shown to react with an alkyne in the presence of parahydrogen to form alkyl hydrides, such as Pd(bcope)(CHPhCH2Ph)(H), that are detectable by NMR spectroscopy because the proton resonances of the alkyl arm appear with strongly enhanced signal strengths.