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The curing of polyester-based clearcoats has been studied by using thermal analysis methods. Polyester resins are used as raw materials for coil coatings. The aim of this work was to [...]

Acute infections of the middle ear (acute otitis media, or AOM) often occur following infections of the respiratory tract. AOM is the most common problem when a patient complains of an ear ache. Although usually caused by bacteria, AOM are frequently associated with viral infections of the respiratory system including respiratory syncytial virus (RSV), influenza viruses (flu), or adenoviruses. Viral proteins or antigens are frequently found within the fluid of the middle ear and have been measured in 18 to 24 percent of children with AOM. Antibodies against certain viruses have also been measured in the fluid contained in the ears of patients with AOM. Thus, it is hypothesized that some cases of AOM are caused by these virus. Certain children, particularly those who are prone to recurrent bouts of AOM, are reported to have a decreased ability to produce antibodies when they are inoculated with pneumococcal vaccine, and may have a generalized decrease in their ability to ward-off disease. The current study investigates the ability of children to produce antibodies against influenza A and adenoviruses during the first year of life and to correlate the ability to manufacture these antibodies with the rate of AOM. The level of antibody protection in this group of 113 was examined from birth to three years of age. During the first six months of life the antibody protection, as expected, declined and was followed by a gradual increase. Thirteen of the children ultimately developed recurrent AOM which proved to be unrelated to level of protective antibodies.

This paper explores shear and extensional rheological behavior of unimodal, metallocene-catalyzed polyethylenes with low contents of long-chain branching (LCB). The polymers were produced in semibatch slurry polymerizations with methylaluminoxane (MAO) activated metallocene catalysts bis(n-butylcyclopentadienyl)hafnium dichloride (1), rac-[ethylenebis(2-tert-butyldimethylsiloxy)indenyl)]zirconium dichloride (2), rac-[ethylenebis(1-tert-butyldimethylsiloxy)indenyl)]zirconium dichloride (3), and rac-[ethylenebis(1-triisopropylsiloxy)indenyl)]zirconium dichloride (4). Melt properties in low oscillatory shear, in contrast to molecular weight and molecular weight distribution data from gel permeation chromatography, suggested that the polymers prepared with the ethylene-bridged complexes 2, 3, and 4 contain small but different amounts of LCB. In the melt uniaxial elongation experiments, the long-chain branched polymers exhibited strain hardening at all extension rates (rate range was from 1.0 to 0.01 s^-1) with continual increase in strain hardening toward low strain rates. Unexpectedly, the behavior in LVE regime low shear and uniaxial elongation in the nonlinear range arranged the polymers in dissimilar order of apparently increasing LCB. Even though both these rheological techniques are sensitive to the molecular structure, they evidently reveal different features of it. Variation in the distribution (topology) of the long-chain branching due to differences in catalyst systems offers a plausible explanation of the differences in uniaxial elongation.

Linear and long chain branched ethene homopolymers and copolymers with 1-hexene were produced with metallocene catalysts. The presence and absence of long chain branching in the polymers was studied by dynamic rheological and gel permeation chromatography−on-line viscometry analysis. Long chain branched polymers were produced with 1- and 2-siloxy-substituted derivatives of rac-Et(Ind)2ZrCl2/MAO and MeSi(C5Me4)(N-t-Bu)TiCl2/MAO. As judged by the rheological behavior, n-ButCp2ZrCl2/MAO produced linear chains, as did the meso form of one of the substituted Et(Ind)2ZrCl2 catalyst structures. The rheological behavior of the polymers was affected by the polymerization conditions, especially by the addition of comonomer and the partial pressures of ethene and hydrogen. In addition, the slurry solvent was relevant to some of the catalysts. The effects of catalyst activity and different mass transfer limitations on the long chain branching were studied. As was evident from the rheological behavior, the long chain branching could be controlled by both the choice of the catalyst and the polymerization conditions. The rheological behavior is discussed with reference to the content of the long chain branches and the structure of the branching.

Ethene homopolymers and ethene copolymers with 1-hexene were prepared by Et[Ind]2ZrCl2/MAO and Et[IndH4]2ZrCl2/MAO catalyst systems in slurry polymerizations. The melt behavior of the polymers was studied with small amplitude dynamic rheological measurements. The low-frequency complex viscosity of the polymers was higher than expected on the basis of their GPC molecular weights. Furthermore, the polymers exhibited elevated activation energy for flow. The polymers catalyzed by Et[Ind]2ZrCl2/MAO had an Arrhenius-type flow activation energy of 50−60 kJ/mol, and those catalyzed by Et[IndH4]2ZrCl2/MAO a somewhat lower value of 40 kJ/mol. Branching could be detected by ¹³C NMR in homopolyethene samples polymerized by Et[Ind]2ZrCl2/MAO. We suggest that these properties are due to long-chain branching that occurs via in situ incorporation of vinyl-terminated polyethene macromonomers. With Et[Ind]2ZrCl2/MAO the polymerization parameters affecting the rheological behavior most were ethene partial pressure and comonomer concentration, whereas with Et[IndH4]2ZrCl2/MAO the major factor was the amount of hydrogen.

In the solid-state structure of the Schiff base salen [salen = N,N‘-ethylenebis(salicylideneiminato)] zirconium dichloride complex Zr(salen)Cl2(THF), C20H22Cl2N2O3Zr, a quadridentate ligand, occupies four sites in the pseudopentagonal bipyramidal coordination. The coordination sphere is completed by one THF molecule, and two chloride ions are forced into the trans-position. Removal of THF, while Zr(salen)Cl2(THF) is heated in toluene, leads to a six-coordinated complex with the two chloride ligands assuming the cis-position. This property was successfully utilized in the preparation of a homogeneous Zr(salen)Cl2 catalyst precursor. Heating of Zr(salen)Cl2(THF) in toluene in the presence of SiO2 causes deposition of Zr(salen)Cl2 on to the silica support, producing a heterogeneous catalyst, which shows an acceptable activity in ethylene polymerization at 80 °C and at low ethylene pressures in the presence of the cocatalyst methylaluminoxane.

Ethylene and propylene were copolymerized with 10-undecen-1-ol, using stereorigid Et[Ind]2ZrCl2, Me2Si[Ind]2ZrCl2, Me2Si[2-MeInd]2ZrCl2, and Me2Si[2-Me-4,5-BenzoInd]2ZrCl2 catalysts activated with methylaluminoxane (MAO). As a reference, ethylene copolymerization was also carried out with the nonstereospecific catalyst [Ind]2ZrCl2/MAO. Characterization of the copolymers by ¹³C and ¹H NMR spectroscopy revealed that the polymerization product was a true copolymer and that the conversion of the polar comonomer was strongly favored by the chiral geometry of the catalyst. The pretreatment of 10-undecen-1-ol with MAO before initiating the copolymerization increased the ethylene polymerization rate markedly and slightly improved the reactivity of the polar comonomer. A major improvement in the polymerization rate of 10-undecen-1-ol was obtained when the polymerization temperature and Al/Zr mole ratio were increased.