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Diethylbis(2,2'-bipyridine)iron-MAO. A very active and sterospecific catalyst for 1,3-diene polymerization
No full textAddition polymerization of norbornene with AIEt2Cl-TiCl4 and rac-[(C2H4)(Ind)2]ZrCl2-MAO. Formation of two different crystalline polymers
No full textPolymerization of 4-methyl-1,3-pentadiene with catalysts based on cyclopentadienyl titanium dichloride: Effect of anti/syn isomerism on the allyl group on the chemoselectivity and role of backbiting coordination in 1,3-diene polymerization
No full textDiethylbis(2,2'-bipyridine) iron-MAO: a very active and stereospecific system for the polymerization of some 1,3-dienes
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Recent Developments in Lanthanide Catalysts for 1,3-Diene Polymerization
No full textACS Symposium Series - Olefin Polymerization: Emerging Frontiers.Published by the American Chemical Society (Editors P. Arjunan, J.E. McGrath, T.L. Hanlon
Helical Structure of 2,3-exo-Disyndiotactic Polynorbornene
No full textNorbornene (NB) has been polymerized by many catalysts and different types of polymers have
been obtained. Of particular interest is the vinyl-type polynorbornene (PNB), which has industrial
relevance for optical and electronic applications. Most of the catalysts so far identified for vinyltype
polymerization of norbornene give polymers that are amorphous by X-ray examination
because of their low tacticity[1]. Crystalline polymers, however, have been obtained with some
catalysts: Al(iBu)3-TiCl4
[2]; ansa-zirconocene-MAO (MAO = methylaluminossane)[3]; CrCl2(L)2-
MAO (L = bidentate phosphine)[4]. The polymerization with metallocene proceeds by means of a
cis-exo monomer insertion, but a C7 linkage is formed as a result of a -bond methatesis reaction.
Due to the formation of the C7 linkage, metallocene PNBs cannot be considered of vinyl–type. The
crystalline PNB obtained with the chromium system MAO-CrCl2(dppa) has a 2,3-exo-diheterotactic
structure, consisting of stereoregular sequences of mr triads.
As mentioned, a crystalline PNB was obtained in 1963 with Al(iBu)3-TiCl4, but its structure was not
investigated. Metathesis reactions as those observed with zirconocene catalysys are less common
with Ti catalysts, and therefore it appeared of interest to examine the structure of the TiCl4-PNB. In
a previous Note we reported on the oligomerization of norbornene (NB) using the catalyst system
AlEt2Cl-TiCl4 at a monomer/titanium molar ratio of about 11. In addition to other oligomers, a
crystalline heptamer was isolated having a stereoregular 2,3-exo-disyndiotactic structure[5]. As a
continuation of this work we have now examined the polymerization of NB at higher
monomer/titanium molar ratios, using the same catalyst, under the same conditions. Products of
high molecular weight have been obtained, all consisting of an amorphous fraction soluble in
diethyl ether and a crystalline fraction, part of which is soluble in boiling toluene. In this poster
communication we report that the crystalline fractions obtained at high monomer/TiCl4 ratio consist
of polymers having a 2,3-exo-disyndiotactic structure as the heptamer
The crystalline structure of the 2,3-exo-disyndiotactic polynorbornene
No full textViene descritto l’ottenimento di polinorbornene cristallino 2,3 disindiotattico, avente un punto di decomposizione senza fusione tra 380 e 400 °C, caratterizzato da insolubità in idrocarburi aromatici a temperatura ambiente e parziale solubilità in toluene all’ebollizione.
Vengono anche descritti il suo processo di preparazione e le nuove strutture clatrate comprendenti le eliche polimeriche del PNB provviste di cavità tubolari interne
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