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Observation of Different Catalytic Activity of Various 1-Olefins during Ethylene/1-Olefin Copolymerization with Homogeneous Metallocene Catalysts  [PDF]
Mingkwan Wannaborworn,Piyasan Praserthdam,Bunjerd Jongsomjit
Molecules , 2011, DOI: 10.3390/molecules16010373
Abstract: This research aimed to investigate the copolymerization of ethylene and various 1-olefins. The comonomer lengths were varied from 1-hexene (1-C6) up to 1-octadecene (1-C18) in order to study the effect of comonomer chain length on the activity and properties of the polymer in the metallocene/MAO catalyst system. The results indicated that two distinct cases can be described for the effect of 1-olefin chain length on the activity. Considering the short chain length comonomers, such as 1-hexene, 1-octene and 1-decene, it is obvious that the polymerization activity decreased when the length of comonomer was higher, which is probably due to increased steric hindrance at the catalytic center hindering the insertion of ethylene monomer to the active sites, hence, the polymerization rate decreased. On the contrary, for the longer chain 1-olefins, namely 1-dodecene, 1-tetradecene and 1-octadecene, an increase in the comonomer chain length resulted in better activity due to the opening of the gap aperture between Cp(centroid)-M-Cp-(centroid), which forced the coordination site to open more. This effect facilitated the polymerization of the ethylene monomer at the catalytic sites, and thus, the activity increased. The copolymers obtained were further characterized using thermal analysis, X-ray diffraction spectroscopy and 13C-NMR techniques. It could be seen that the melting temperature and comonomer distribution were not affected by the 1-olefin chain length. The polymer crystallinity decreased slightly with increasing comonomer chain length. Moreover, all the synthesized polymers were typical LLDPE having random comonomer distribution.
Investigation on chain structure of LLDPE obtained by ethylene in-situ copolymerization with DSC and XRD
YanJie Wang,WeiDong Yan
Chinese Science Bulletin , 2007, DOI: 10.1007/s11434-007-0093-4
Abstract: Thermal segregations of LLDPE were treated with successive self-nucleation/annealing (SSA) on differential scanning calorimetry (DSC). Information on molecular heterogeneity of LLDPE was obtained. After SSA was treated, the multiple endothermic peaks were observed in the DSC thermograms during heating experiment. It is obtained that the thickness of different lamellas formed by segments of various lengths was 4–10 nm. X-ray diffraction (XRD) results showed that the crystallites dimensions of various reflections were about several dozens of nanometers. The ethylene/α-olefin copolymers and the copolymer via in-situ copolymerization were similar to each other for molecular heterogeneity and XRD characteristics, which revealed that it was possible to use the ethylene/α-olefin copolymers to simulate the copolymer via in-situ copolymerization of ethylene to simplify the complexity of the structure of the ethylene in-situ copolymer.
STUDIES ON CRYSTALLINITY AND CRITICAL CRYSTALLINE SEQUENCE LENGTH OF ETHYLENE/a-OLEFIN COPOLYMERS
乙烯-α-烯烃共聚物的结晶性能及其临界序列结晶长度的研究

LI San-xi,MO Zhi-shen,ZHANG Hong-fang,PANG De-ren,HUANG Bao-tong,
李三喜
,莫志深,张宏放,庞德仁,黄葆同

高分子学报 , 1991,
Abstract: The crystallinity of ethylene/a-olefin copolymers, which was prepared by copolymerization of ethylene and a-olefins with heterogeneous Ziegler-Natta catalyst made by chemical reaction, was studied by WAXD, DSC, and PLM methods.The results of WAXD showed that the crystallite size and degree of crystallinity decrease and the parameters of unit cell increase with increase content of a-olefin in copolymers. On the other hand, the crystallite size and degree of crystallinity of the copolymers after heat treatment obviously increase, while parameters of unit cell decrease. Both the critical crystalline sequence lengthes and the value of k obtained increase in the order of EPe
The allylic chalcogen effect in olefin metathesis  [cached]
Yuya A. Lin,Benjamin G. Davis
Beilstein Journal of Organic Chemistry , 2010, DOI: 10.3762/bjoc.6.140
Abstract: Olefin metathesis has emerged as a powerful tool in organic synthesis. The activating effect of an allylic hydroxy group in metathesis has been known for more than 10 years, and many organic chemists have taken advantage of this positive influence for efficient synthesis of natural products. Recently, the discovery of the rate enhancement by allyl sulfides in aqueous cross-metathesis has allowed the first examples of such a reaction on proteins. This led to a new benchmark in substrate complexity for cross-metathesis and expanded the potential of olefin metathesis for other applications in chemical biology. The enhanced reactivity of allyl sulfide, along with earlier reports of a similar effect by allylic hydroxy groups, suggests that allyl chalcogens generally play an important role in modulating the rate of olefin metathesis. In this review, we discuss the effect of allylic chalcogens in olefin metathesis and highlight its most recent applications in synthetic chemistry and protein modifications.
The Role of the Conjugate Bridge in Electronic Structures and Related Properties of Tetrahydroquinoline for Dye Sensitized Solar Cells  [PDF]
Cai-Rong Zhang,Li Liu,Jian-Wu Zhe,Neng-Zhi Jin,Yao Ma,Li-Hua Yuan,Mei-Lin Zhang,You-Zhi Wu,Zi-Jiang Liu,Hong-Shan Chen
International Journal of Molecular Sciences , 2013, DOI: 10.3390/ijms14035461
Abstract: To understand the role of the conjugate bridge in modifying the properties of organic dye sensitizers in solar cells, the computations of the geometries and electronic structures for 10 kinds of tetrahydroquinoline dyes were performed using density functional theory (DFT), and the electronic absorption and fluorescence properties were investigated via time dependent DFT. The population analysis, molecular orbital energies, radiative lifetimes, exciton binding energies (EBE), and light harvesting efficiencies (LHE), as well as the free energy changes of electron injection ( ) and dye regeneration ( ) were also addressed. The correlation of charge populations and experimental open-circuit voltage ( V oc) indicates that more charges populated in acceptor groups correspond to larger V oc. The elongating of conjugate bridge by thiophene units generates the larger oscillator strength, higher LHE, larger absolute value of , and longer relative radiative lifetime, but it induces the decreasing of EBE and . So the extending of conjugate bridge with thiopene units in organic dye is an effective way to increase the harvest of solar light, and it is also favorable for electron injection due to their larger . While the inversely correlated relationship between EBE and LHE implies?that the dyes with lower EBE produce more efficient light harvesting.
Light-induced olefin metathesis  [cached]
Yuval Vidavsky,N. Gabriel Lemcoff
Beilstein Journal of Organic Chemistry , 2010, DOI: 10.3762/bjoc.6.127
Abstract: Light activation is a most desirable property for catalysis control. Among the many catalytic processes that may be activated by light, olefin metathesis stands out as both academically motivating and practically useful. Starting from early tungsten heterogeneous photoinitiated metathesis, up to modern ruthenium methods based on complex photoisomerisation or indirect photoactivation, this survey of the relevant literature summarises past and present developments in the use of light to expedite olefin ring-closing, ring-opening polymerisation and cross-metathesis reactions.
Investigation on Chain Structure of LLDPE Obtained by Ethylene In-situ Copolymerization with DSC and XRD
Investigation on chain structure of LLDPE obtained by ethylene in-situ copolymerization with DSC and XRD

wang yanjie yan weidong,
WANG
,YanJie,YAN,WeiDong

科学通报(英文版) , 2007,
Abstract: Thermal segregations of LLDPE were treated with successive self-nucleation/annealing (SSA) on differential scanning calorimetry (DSC). Information on molecular heterogeneity of LLDPE was obtained. After SSA was treated, the multiple endothermic peaks were observed in the DSC thermograms during heating experiment. It is obtained that the thickness of different lamellas formed by segments of various lengths was 4–10 nm. X-ray diffraction (XRD) results showed that the crystallites dimensions of various reflections were about several dozens of nanometers. The ethylene/α-olefin copolymers and the copolymer via in-situ copolymerization were similar to each other for molecular heterogeneity and XRD characteristics, which revealed that it was possible to use the ethylene/α-olefin copolymers to simulate the copolymer via in-situ copolymerization of ethylene to simplify the complexity of the structure of the ethylene in-situ copolymer. Supported by the National Natural Science Foundation of China (Grant No. 50573018) and Doctoral Foundation of Hebei Province (Grant No. 05547003D-6)
Olefin metathesis in nano-sized systems  [cached]
Didier Astruc,Abdou K. Diallo,Sylvain Gatard,Liyuan Liang
Beilstein Journal of Organic Chemistry , 2011, DOI: 10.3762/bjoc.7.13
Abstract: The interplay between olefin metathesis and dendrimers and other nano systems is addressed in this mini review mostly based on the authors’ own contributions over the last decade. Two subjects are presented and discussed: (i) The catalysis of olefin metathesis by dendritic nano-catalysts via either covalent attachment (ROMP) or, more usefully, dendrimer encapsulation – ring closing metathesis (RCM), cross metathesis (CM), enyne metathesis reactions (EYM) – for reactions in water without a co-solvent and (ii) construction and functionalization of dendrimers by CM reactions.
Tris(η5-cyclopentadienyl)hafnium(III)
Vladimir V. Burlakov,Perdita Arndt,Anke Spannenberg,Uwe Rosenthal
Acta Crystallographica Section E , 2011, DOI: 10.1107/s1600536811014516
Abstract: In the crystal structure of the title compound, [Hf(C5H5)3], three cyclopentadienyl ligands surround the HfIII atom in a trigonal–planar geometry. The molecule lies on a sixfold inversion axis.
Olefin hydrogenation with iron carbonyls as catalysts
Baibich, I.M;Garcia, R.R.P;
Journal of the Brazilian Chemical Society , 1997, DOI: 10.1590/S0103-50531997000300005
Abstract: the use of [fe(co)5] , [fe2(co)9] and [fe3(co)12] as catalytic precursors in the hydrogenation reactions of cyclohexene and 1-hexene was investigated. a photochemical reactor with h2 flux and uv-vis continuous irradiation was used for these studies. the infrared spectra of the samples showed the formation of [fe(co)4(olefin)] and [hfe(co)3(p-allyl)] as intermediates. the activity of [fe2(co)9] in the hydrogenation of cyclohexene was higher (66.6%) than the activity of the other iron carbonyls (43.0% [fe(co)5], [fe3(co)12]). the competition between isomerization and hydrogenation in the reaction of 1-hexene was studied. the isomerization rate was much higher than the hydrogenation rate and the polynuclear species provided faster isomerizations than [fe(co)5]. the alkane conversions were: 60.0% ([fe(co)5], [fe3(co)12]) and 75.4% ([fe2(co)9]), showing that for the 1-hexene hydrogenation [fe2(co)9] also exhibited the highest activity.
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