Synthesis and barrier properties of poly(ε-caprolactone)-layered silicate nanocomposites

A new polymer-ceramic nanocomposite has been synthesized consisting of well-dispersed, two-dimensional layers of an organically modified mica-type silicate (MTS) within a degradable poly(ε-caprolactone) matrix. A protonated amino acid derivative of MTS was used to promote delamination/dispersion of the host layers and initiate ring-opening polymerization of ε-caprolactone monomer, resulting in poly(ε-caprolactone) chains that are ionically bound to the silicate layers. The polymer chains can be released from the silicate surface by a reverse ion-exchange reaction and were shown to be spectroscopically similar to pure poly(ε-caprolactone). Thick films of the polymer nanocomposite exhibit a significant reduction in water vapor permeability that shows a linear dependence on silicate content. The permeability of nanocomposite containing as low as 4.8% silicate by volume was reduced by nearly an order of magnitude compared to pure poly(ε-caprolactone). © 1995 John Wiley & Sons, Inc.     

Chemistry of chloroethylenes on Cu(100): bonding and reactions

The bonding and reactions of chloroethylenes (vinyl chloride, trans- and cis-dichloroethylene, trichloroethylene) on a Cu(100) surface have been investigated by temperature-programmed desorption and reaction, near-edge X-ray absorption fine structure (NEXAFS) studies and measurements of changes of the surface work function. The monolayer molecules adsorb molecularly intact at 95 K via π coordination. The molecules orient with their molecular planes parallel to the surface with little increase (<0.02 Å) in the C---C bond distance compared with the gas phase values. The degree of thermal dissociation increases with the extent of halogenation, and no chlorine is present in the hydrocarbon reaction products liberated from the surface. Both cis- and trans-1.2-chloroethylene produce acetylene and a small amount of benzene, while dissociation of trichloroethylene generates acetylene and deposits a carbon residue on the surface. Vinyl chloride desorbs from Cu(100) without reaction.     

Non-classical law of the iterated logarithm behaviour for trimmed sums

Summary We study the law of the iterated logarithm for the partial sum of i.i.d. random variables when the r _n largest summands are excluded, where r _n=o(log logn). This complements earlier work in which the case log log_n=O(r_n) was considered. A law of the iterated logarithm is again seen to prevail for a wide class of distributions, but for reasons quite different from previously.Research supported in part by NSF Grant DMS-8501732