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Oxyanions form a new class of catalysts for group-transfer polymerization (GTP) of acrylic monomers.Active catalysts in this class include aliphatic and aromatic carboxylates, phenolates, sulfinates, phosphinates, sulfonamidates, perfluoroalkoxides, nitrite, and cyanate. Catalytic activity is found in oxyanions whose conjugate acids have a p (in DMSO) within the range 4.5-23. Best results in terms of livingness and polydispersity of the resulting polymers are obtained with the lowest operable concentrations of the most active catalysts and with somewhat higher concentrations of catalysts of moderate activity. Bioxyanions (1:1 complexes of oxyanions with their conjugate acids) also are active but show reduced activity compared to the corresponding monooxyanions. They give better control of molecular weight than is obtained with the corresponding monooxyanions. In contrast to the more potent catalysts, the weaker catalysts show little activity at temperatures substantially below room temperature. Relative catalyst efficiency correlates well with pKa(DMSO) of the conjugate acids of the corresponding catalysts. The stereochemistry of PMMA prepared with oxyanion catalysts does not differ substantially from that of PMMA prepared with bifluoride catalysis.

The effect of nanoparticles (NP) on chain dimensions in polymer melts has been the source of considerable theoretical and experimental controversy. We exploit our ability to ensure a spatially uniform dispersion of 13 nm silica NPs miscible in polystyrene melts, together with neutron scattering, x-ray scattering, and transmission electron microscopy, to show that there is no measurable change in the polymer size in miscible mixtures, regardless of the relative sizes of the chains and the nanoparticles, and for NP loadings as high as 32.7 vol%. Our results provide a firm basis from which to understand the properties of polymer nanocomposites.

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Scheme I here allows us to express these in terms of the three constants k\, kIC, and krt. By methods previously described,2311 the retention ratiosp = 41.8/58.2 = 0.72, q = 72/28 = 2.57, and pq -1.85 lead to 0.23kTC as the rate constant for ring closure to 2 and 0.5krt the rate constant for ring closure to 1. In view of the low conversion to product and small fraction of isomerization we neglect the "recycle" effect of product formation from preisomerized olefin, and note that c/s-2-butene gave 0.129 mol of trans olefin and 0.0298 mol of 1, indicating that the rate constant for cleavage that competes with closure to 1 is equal to (0.129/0.0298)0.5kIt = 2.2kTt.Since /nro-2-butene gave 0.0667 mol of cw-2-butene and 0.0125 mol of 2, the cleavage that competes with closure to 2 has a rate constant of (0.0667/0.0215)• 0.23kTC = 0.71 kIC, as shown in Scheme I. The competition between ethylene and 2-butene is analogous to that between butadiene and 2,4-hexadiene, previously investigated5 at 80°. The relative rates of addition of 1, l-dichloro-2,2-difluoroethylene ("1122") to one double bond of butadiene, frares-piperylene, and trans,trans-2,4-hexadiene are 1.0, 1.65, and 0.046.The enhancement due to the methyl group on the allylic system in the biradical is much less than the hindrance imposed by the methyl group at the site of the first bond formation. The overall factor of 10 between ethylene and 2-butene at 175°seems quite in accord with the factor of 22 at 80°between butadiene and 2,4hexadiene. By contrast, in the concerted Diels-Alder reaction, methyl substitution at the ends of the conjugated system brings about an increase in reaction rate (12-fold toward maleic anhydride at 175°6).(2) (a) L.

Society, and the Shell Corporation for support of this work.(6) All compounds exhibited satisfactory spectral and physical properties. The stereochemistry of intermediates 3 and 4 follows from their 100-MHz nmr spectra.(7) The yields reported are for isolated products. (8) Similar sulfoxide to olefin transformations have been recently reported by B. M. Trost and T. N. Salzmann, J. Amer. Chem. Soc., in press. We thank Professor Trost for communicating an account of this work to us prior to its publication.