UHMWPE/SBA-15 nanocomposites synthesized by in situ polymerization

Different nanocomposites have been attained by in situ polymerization based on ultra-high molecular weight polyethylene (UHMWPE) and mesoporous SBA-15, this silica being used for immobilization of the FI catalyst bis [N-(3-tert-butylsalicylidene)-2,3,4,5,6-pentafluoroanilinato] titanium (IV) dichloride and as filler as well. Two distinct approaches have been selected for supporting the FI catalyst on the SBA-15 prior polymerization. A study on polymerization activity of this catalyst has been performed under homogenous conditions and upon heterogenization. A study of the effect of presence of mesoporous particles and of the immobilization method is also carried out. Moreover, the thermal characterization, phase transitions and mechanical response of some pristine UHMWPEs and UHMWPE/SBA-15 materials have been carried out. Relationships with variations on molar mass, impregnation method of catalyst and final SBA-15 content have been established

MCM-41 as Nanofiller in Polyethylene Hybrid Materials

Mesoporous MCM-41 exhibits a stable framework structure, well-defined nanopores and a large surface area. When combined with metallocene polymerisation catalyst, these mesoporous materials, provide a unique route for preparing polyolefin-based nanocomposites by in situ polymerisation

UHMWPE/HDPE in-reactor blends, prepared by in situ polymerization: synthetic aspects and characterization

This work covers the synthesis and characterization of in-reactor Ultra-High Molecular Weight Polyethylene/ High Density Polyethylene, UHMWPE/HDPE, blends by in situ polymerization in a single reactor, through dual catalyst immobilization. These blends are synthesized combining two different catalysts (one for each targeted molar mass) co-immobilized in mesoporous Santa Barbara Amorphous, SBA-15, particles. First, the ethylene polymerization behavior is investigated, under different polymerization conditions. Then, studies on the thermal, mechanical and rheological characteristics of the produced in-reactor blends are presented and their performance is compared and discussed in a comprehensive way. Moreover, the effect of different filler contents on the properties exhibited by the resulting materials is investigated. Results have shown that these in-reactor UHMWPE/HDPE blends exhibit a complex thermal, mechanical and rheological behavior, which depends mainly on the proportion between the two polymer components and on the amount of SBA-15.info:eu-repo/semantics/publishedVersio

New HDPE/MCM41 nanocomposites with improved mechanical performance: synthesis and characterizatio

Ordered mesoporous silicas with a channel structure of well-defined geometries and dimensions at nanometer scale are excellent candidates to host intercalation reactions. In recent years, our research group has shown that mesoporous silicas of the M41S class combined with metallocene complexes give rise to excellent supported catalysts for ethylene polymerisation. Due to the support characteristics, the reaction is allowed to occur in the channels and in this way hybrid organic-inorganic materials can be prepared within a large range of nanofiller concentration. These HDPE/MCM-41 nanocomposites exhibit an improved mechanical performance and an easier degradability due to the additional role of MCM-41 as a promoter for PE degradation

Measurement of Exclusive rho^0 rho^0 Production in Two-Photon Collisions at High Q^2 at LEP

Exclusive rho rho production in two-photon collisions involving a single highly virtual photon is studied with data collected at LEP at centre-of-mass energies 89GeV < \sqrt{s} < 209GeV with a total integrated luminosity of 854.7pb^-1 The cross section of the process gamma gamma^* -> rho rho is determined as a function of the photon virtuality, Q^2 and the two-photon centre-of-mass energy, Wgg, in the kinematic region: 1.2GeV^2 < Q^2 < 30GeV^2 and 1.1GeV < Wgg < 3GeV

Search for a Higgs Boson Decaying to Weak Boson Pairs at LEP

A Higgs particle produced in association with a Z boson and decaying into weak boson pairs is searched for in 336.4 1/pb of data collected by the L3 experiment at LEP at centre-of-mass energies from 200 to 209 GeV. Limits on the branching fraction of the Higgs boson decay into two weak bosons as a function of the Higgs mass are derived. These results are combined with the L3 search for a Higgs boson decaying to photon pairs. A Higgs produced with a Standard Model e+e- --> Zh cross section and decaying only into electroweak boson pairs is excluded at 95% CL for a mass below 107 GeV

Search for an invisibly decaying Higgs boson in e^+e^- collisions at \sqrt{s} = 183 - 189 GeV

A search for a Higgs boson decaying into invisible particles is performed using the data collected at LEP by the L3 experiment at centre-of-mass energies of 183 GeV and 189 GeV. The integrated luminosities are respectively 55.3 pb^-1 and 176.4 pb^-1. The observed candidates are consistent with the expectations from Standard Model processes. In the hypothesis that the production cross section of this Higgs boson equals the Standard Model one and the branching ratio into invisible particles is 100%, a lower mass limit of 89.2 GeV is set at 95% confidence level

Measurement of Exclusive rho+rho- Production in Mid-Virtuality Two-Photon Interactions and Study of the gamma gamma* -> rho rho Process at LEP

Exclusive rho+rho- production in two-photon collisions between a quasi-real photon, gamma, and a mid-virtuality photon, gamma*, is studied with data collected at LEP at centre-of-mass energies root(s)=183-209GeV with a total integrated luminosity of 684.8pb^-1. The cross section of the gamma gamma* -> rho+ rho- process is determined as a function of the photon virtuality, Q^2, and the two-photon centre-of-mass energy, W_gg, in the kinematic region: 0.2GeV^2 < Q^2 <0.85GeV^2 and 1.1GeV < W_gg < 3GeV. These results, together with previous L3 measurements of rho0 rho0 and rho+ rho- production, allow a study of the gamma gamma* -> rho rho process over the Q^2-region 0.2GeV^2 < Q^2 < 30 GeV^2