1,721,075 research outputs found
“Copolymerization of ethylene with cyclopentene or 2-butene with half-titanocenes based catalysts.”
No full textHalf titanocenes (CpCH2CH2O)TiCl2 (1), (CpCH2CH2OCH3)TiCl3 (2), and CpTiCl3 (3), activated by methylaluminoxane (MAO) were tested in copolymerization of ethylene with internal olefins such as cyclopentene. All the catalysts were able to give incorporation of cyclopentene in polyethylene matrix. 13C NMR analysis of obtained copolymers showed that the catalytic systems have low regiospecificity. In fact, in ethylene–cyclopentene copolymers, cyclic olefin inserts with both 1,2 and 1,3-enchainment. X-ray powder diffraction analysis of these copolymers confirmed that 1,2 inserted cyclopentene units are excluded from crystalline phase, whereas 1,3-cyclopentene units are included, giving rise to expansion of unit cell of crystalline polyethylene. Titanium-based catalysts were investigated also in the copolymerization of ethylene with E and Z-2-butene. Only complex (1) was able to give copolymers and 13C NMR analysis of products showed 2-3, 1-3, and 1-2 insertion of 2-butene. Differential scanning calorimetry analysis displayed that ethylene–cyclopentene, as well as ethylene-2-butene, copolymers are crystalline and their melting point decreases by increasing the comonomer content
Influence of syn and anti substitution on the backbone of NHC-ruthenium catalysts in olefin metathesis
No full textStructural materials: Nanoscale modifiers in advance composites. Healing agent for the activation of self-healing function at low temperature
No full textThe development of smart composites capable of self-repair in aeronautical structures is still at the
planning stage owing to complex issues to overcome. It is critical that self-healing activity functions at
low working temperatures which can reach values as low as – 50°C. Also, another problem concerns
the components’ stability of the proposed composites which are compromised at the cure temperatures
necessary for good performance of the composite.
Here, we show a multifunctional autonomically healing composite with self-healing function
capable at very low temperatures (-50°C). The self-repair function in this self-healing system is based
on the metathesis polymerization of ENB/DCPD blend activated by HG1 catalyst dispersed at
molecular level in the matrix. The formulated material shows a self-healing efficiency of about 72 %
Efficient self-healing resins
No full textMicro-encapsulated monomers and embedded solid catalysts produce
high-performance composites that quickly repair themselves at temperatures
as low as -50C
Ru-based complexes bearing saturated chiral N-heterocyclic carbene ligands: efficient catalysts for olefin metathesis
No full text
Various Alkyne Functionalization Promoted By Coinage Metal N-Heterocyclic Carbene Complexes
No full textSyndiotactic-atactic stereoblock polystyrene obtained with a hapto-flexible catalyst
No full textHalf-titanocene (CpCH2CH2OCH3)TiCl 3 (1), (Cp = cyclopentadienyl), activated by methylaluminoxane (MAO), has been tested in the polymerization of styrene in a suitable range of temperatures, obtaining a new material consisting of syndiotactic-atactic stereoblocks of polystyrene. The monoanionic bidentate ancillary ligand of the titanium based catalyst, consisting of a cyclopentadienyl bearing an alkyl ether, is a hapto-flexible ligand because the ether group can either be coordinated or not to the metal, depending on reaction temperature. Thus, the ether group can give rise to two possible catalytic sites: (i) syndiospecific, when the ether group is not coordinated to the metal center, and (ii) aspecific, when it is coordinated to titanium. Consequently, it produces polymer chains having syndiotactic and atactic stereoblocks. In fact, in the range of temperature considered (0-19 °C), syndiotactic polystyrene was produced at 19 °C, atactic polystyrene at 0 and 5 °C, and syndiotactic-atactic stereoblock polystyrene at 10 and 15 °C
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