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Herein, we report copolymerizations of ethylene (E) and ortho-/meta-/para-fluorostyrenes (SF =oFS/mFS/pFS) by using quinolyl methylene fluorenyl scandium complex (Flu-CH2 -Qu)Sc(CH2 SiMe3 )2 . The copolymerizations proceed in a controlled fashion to afford copolymers composed of "soft" ethylene-fluorostyurene (E-SF ) random segments (Tg =-22.2-5.1 °C) and "hard" crystalline ethylene-ethylene (E-E) segments (Tm =42.3-130.2 °C). The copolymers behave like thermoplastic elastomers at room temperature by showing high stress values up to 39.5 MPa under elongation-at-break above 774 % with elastic recovery over 75 %. The excellent mechanical properties are mainly attributed to the microphase separation of the nanoscale crystalline E-E domain from the amorphous E-SF copolymer matrix proved by AFM, WAXD and SAXS. The mechanism investigation by the density functional theory (DFT) simulation reveals that the steric bulky and electron-withdrawing ligand of the catalytic precursor prefers E propagation to generate long E-E segments, while the incorporation of SF is thermodynamic control.

The cis-1,4 selective copolymerizations of butadiene (BD) with naked polar methylthio- and p-tolylthio-functionalized α-olefins have been investigated by using the thiophene-fused cyclopentadienyl ...

Low-molecular-weight polystyrene (LMPS) is the precursor of a brominated styrene oligomer that is used for small, precise, thin electrical components and an environmentally benign flame-retardant m...

Preparation of polyethylenes containing hydroxy groups has been already industrialized through radical copolymerization under harsh conditions followed by alcoholysis. By contrast, hydroxy-functionalized polypropylene has proven a rather challenging goal in polymer science. Propylene can't be polymerized through a radical mechanism, and its coordination copolymerization with polar monomers is frustrated by catalyst poisoning. Herein, we report a new strategy to reach this target. The coordination polymerization of allenes by rare-earth-metal precursors affords pure 1,2-regulated polyallenes, which are facilely transformed into poly(allyl alcohol) analogues by subsequent hydroboration/oxidation. Strikingly, the copolymerization of allenes and propylene gives unprecedented hydroxy-functionalized polypropylene after post-polymerization modification. Mechanistic elucidation by DFT simulation suggests kinetic rather than thermodynamic control.

Synthesizing functional butadiene–styrene rubber through coordination polymerization is a theoretical challenge for polymer science, since functional monomers usually deactivate to the applied catalyst. Herein, we report the coordination copolymerization of polar para-fluorostyrene (pFS) and butadiene (BD) using pyridyl–methylene–fluorenyl supported complexes [(Py-CH2-Flu)Ln(CH2SiMe3)2(THF)n (Ln = Sc (1a), n = 0; Ln = Lu (1b), n = 1)] and pyridyl–cyclopentadienyl supported complexes [(Py-Cp)Ln(η3-C3H5)2 (Ln = Sc (2a), Lu (2b))]. Strikingly, complexes 2a and 2b exhibited dually >99% syndio- and >95% cis-1,4 regio- selectivities and showed obvious characteristics of living polymerization. The insertion of pFS can be facilely tuned in the full range of 0–100% by changing the pFS-to-BD feed ratio. Diblock P(pFS-BD) copolymers were isolated by concurrent addition of monomers and the kinetics study of the copolymerization reaction revealed that BD had the privilege to coordinate to the active metal center. Interestingly, the polymerizations of BD and pFS via pulse loading of BD afforded multi-block copolymers of a novel type of fluoro styrene–butadiene rubber with high thermal stability (Td = 368 °C). The microstructures of resultant copolymers were confirmed by 1H and 13C NMR measurements and different phase morphologies of the di- and multi-block polymers were displayed through atomic force microscopy (AFM).

The coordination polymerization of polar vinyl monomers is a theoretical challenge since Lewis basic polar groups are usually poisonous to Lewis acidic transition-metal catalysts. In this work, we report the coordination polymerization of polar vinyl heteroaromatic monomers, including 2-vinylfuran (VF), 2-methyl-5-vinylfuran (MVF), 2-vinylbenzofuran (VBF), 2-vinylthiophine (VT), 2-vinylbenzothiophene (VBT) and 2-vinyldibenzothiophene (VDBT), by using the rare-earth-metal complexes 1–4 [(bis(2,6-dimethyl anilido)ketimine)Y(CH2SiMe3)2(THF) (1), (2,4,5,6-Me4-4H-cyclopenta[b]thiophenyl)Sc(CH2SiMe3)2(THF) (2), (Flu-CH2-Py)Sc(CH2SiMe3)2 (3) and (Flu-CH2-Py)Sc(CH2SiMe3)2(THF) (4)]. The polymerizations of vinylfuran derivatives exhibited extremely low activity and gave crosslinked products. Strikingly, high stereo-selectivity coordination polymerization of VBT was achieved successfully with high activity by using complex 4. High-molecular-weight and perfect syndioselective (rrrr > 99%) poly(vinylbenzothiophene) (PVBT) was afforded. In addition, the copolymerization of VBT and styrene (St) proceeded fluently in a wide range of VBT-to-St ratios. The competitive reactivity ratios of rVBT = 3.72 and rSt = 0.42 indicate the gradient sequence distribution of VBT-St copolymers. Moreover, the copolymerization of St and vinyldibenzothiophene (VDBT) can also be realized to give highly thermally stable products, although the homopolymerization of VDBT is rather sluggish due to the sterically hindered dibenzothiophenyl group.

Stereospecific polymerization of polar olefins has always been an attractive but challenging project because the Lewis basic polar groups of monomers are usually poisonous to the Lewis acidic metal centers of the catalysts. In this contribution, thiophene-fused cyclopentadienyl scandium complexes 1—3 were successfully synthesized. Combined with alkylaluminium and organoborate, these complexes showed extremely low activity and no selectivity for 1-hexene polymerization. Surprisingly, highly stereo-selective coordination polymerization of unprotected polar 4-methylthio-1-butene has been achieved in high activity for the first time under the same polymerization conditions. High-molecular-weight (Mn=110×103) and perfectly syn-diotactic (rrrr>99%) poly(4-methylthio-1-butene) (P(MTB)) was afforded. Thus the methylthio-group-assisted mechanism that the unmasked methylthio group promoted the polymerization through σ-π chelation to the active scandium center together with the vinyl group was proposed. Moreover, the methylsulfonyl functionalized syndiotactic poly(1-butene) was also easily prepared by the oxidation of P(MTB). These results provided a new route for the synthesis of functionalized stereo-regular polyolefins.

To shed light on the stereomicrostructure effect on the conformation of helical vinyl polymers, a pair of enantiomeric monomers, (+)-2-[(S)-sec-butoxy]-5-(4′-hexyloxyphenyl)styrene and (−)-2-[(R)-sec-butoxy]-5-(4′-hexyloxyphenyl)styrene, were synthesized and polymerized through radical, anionic and coordination polymerization under various conditions. The presence of strong steric hindrance between the large neighboring biphenyl pendants drove the main chains of the resultant polymers to adopt stable helical conformations in solution. Isotactic-rich polymers displayed optical rotations opposite to those of atactic and syndiotactic-rich ones bearing identical chiral, nonracemic pendant groups but the same sign Cotton effects in the absorption region of biphenyl side groups. This novel phenomenon was attributed to the cooperative effects of the tactic structure and the chiral pendant on the population of the helical sense of the polymer backbone: the chiral ortho-alkoxy terminal made the two phenyl rings of the pendant twist in an identical direction, regardless of the tactic structure, but distinguished the right- from left-handed main chain helices of syndiotactic- and isotactic-rich polymers. This study not only provided the first comprehensive insight into the connections between the main chain spatial configuration, helical conformation and the chiroptical properties but also a convenient way to obtain vinyl polymers with various chiral secondary structures from the same monomer.

Rare earth metal-based complexes can catalyze ethylene/styrene copolymerization to give copolymers with long syndiotactic polystyrene sequences. Here, sequence-controlled ethylene/styrene copolymerization was achieved by regulating the electronic and steric properties of scandium precursors. When a thiophene-fused cyclopentadienyl scandium complex 1, (2,4,5,6-Me4-4H-cyclopenta[b]thiophenyl)Sc(CH2SiMe3)2, was used, a copolymer with long syndiotactic polystyrene sequences was obtained. The tetrahydrofuran (THF) adduct of complex 1 (1·THF) showed lower activity to give a copolymer with short polystyrene sequences owing to an increase in the steric effects around the metal center. The pyridine adducts 1·Py and 1·PyF5 were totally inert. Under the same conditions, complex 2 ((2,5-dimethyl-3-phenyl-4-H-cyclopenta[b]thiophenyl)Sc(CH2SiMe3)2), an analog of 1, incorporated styrene discretely into the copolymer to form a “pseudo random” microstructure. Complex 3 bearing a bulky and less electron-donating constrained-geometry configuration ligand ((Flu-CH2–Py)Sc(CH2SiMe3)2) could catalyze copolymerization in a livingness manner to afford copolymers containing mainly the alternating ethylene/styrene sequence, where a fast and reversible chain-transfer reaction to aluminum alkyl was observed. The influences of structural and electronic factors of the scandium precursors, such as the steric bulkiness of a ligand and incorporation of a Lewis base to the active metal center, on the catalytic activity and sequence distribution of the resulting copolymers were elucidated.

Ligand-free Ln (CH2SiMe3)3 (THF)2 (1: Ln = Sc; 2: Ln = Lu; 3: Ln = Er; 4: Ln = Y) and La(CH2C6H4-o-NMe2)3 (5) are employed as the initiators for ring-opening polymerization (ROP) of rac-lactide (rac-LA). Complex 4 solely is active but uncontrolled, while complex 1 is inert. In presence of excess benzhydrol, complexes 1–5 can promote the ROP of LA smoothly, in which the molecular weight distribution values of the resultant polymer are related to the radii of the rare-earth metals. Complex 1 displays high activity for the controlled ROP of LA, in which the benzhydrol act a dual role as chain-transfer agent and activator. The polymerizations proceed smoothly and efficiently in a wide range of benzhydrol feeding (3–150 equiv). The molecular weights of the obtained PLAs can be precisely controlled by the monomer loading with respect to that of benzhydrol, while the molecular weight distribution (MWD) maintains a very narrow level (PDI = 1.05–1.18). Every scandium centre by means of chain-transfer reaction with benzhydrol to generate the active species Sc(OCHPh2)3·THF (6), grows apparently up to 150 PLA polymer chains, showing a typical feature of an immortal polymerization.

The crystallization behavior of syndiotactic polystyrene (sPS) γ form undergoing annealing at various temperatures was investigated using the thermodynamic phase diagram based on Strobl’s crystallization theory. On the basis of the differential scanning calorimetric results, it was observed that γ form melt-recrystallization occurred at a higher temperature with the increasing lamellar thickness, which resulted from the pre-annealing at the elevating temperature after acetone induced crystallization. Further temperature dependent small-angle X-ray scattering (SAXS) measurement revealed the evolution of the γ form lamellae upon heating until phase transition, involving three different regimes: lamellae stable region (25−90 °C), melt-recrystallization region (90−185 °C) and pre-phase transition region (185−195 °C). As a result, recrystallization line, equilibrium recrystallization line and melting line were developed for the sPS γ form crystallization process. Since the melt of γ form involved a γ-to-α/β form phase transition, the melting line was also denoted as the phase transition line in this special case. Therefore, the equilibrium crystallization temperature and melting (phase transition) temperatures were determined at around 390 and 220 °C on the basis of the thermodynamic phase diagram of the sPS γ form.

A highly efficient strategy for the synthesis of polylactide with the UV absorption ability was established by employing a Salan-yttrium complex (acting as a fast runing catalyst) combined with large excess hydroxyl functionalized benzophenone, BP′-OH. During polymerization, BP′-OH, acting as the chain transfer agent, attached to the active rare-earth metal catalyst via a rapid-reversible exchange reaction to initiate the polymerization. Thus, more polyester chains appeared to grow from one active metal species, and the UV absorption fragments were incorporated into the polymer chains at specific sites, in situ. A high productivity up to 1000 molLA/mol(Salan-Y) was successfully achieved and 100 BP′-labeled PLA chains grew from each active metal center.

Styrene underwent unprecedented coordination–insertion copolymerization with naked polar monomers (ortho-/meta-/para-methoxystyrene) in the presence of a pyridyl methylene fluorenyl yttrium catalyst. High activity (1.26×106 g molY−1 h−1) and excellent syndioselectivity were observed, and high-molecular-weight copolymers (24.6×104 g mol−1) were obtained. The insertion rate of the polar monomers could be adjusted in the full range of 0–100 % simply by changing the loading of the polar styrene monomer. Strikingly, the copolymers had tapered, gradient, and even random sequence distributions, depending on the position of the polar methoxy group on the phenyl ring and thus on its mode of coordination to the active metal center, as shown by tracking the polymerization process and DFT calculations.

The unprecedented highly cis-1,4 selective (>99%) coordination–insertion polymerization of the polar monomer 2-(4-methoxyphenyl)-1,3-butadiene (2-MOPB) has been achieved using a β-diketiminato yttrium bis(alkyl) complex to afford a hydrophilic plastic polymer P(2-MOPB) with a water contact angle of 87.7° and glass transition temperature of 34.2 °C. The copolymerization of polar 2-MOPB and non-polar isoprene has also been successfully realized for the first time to produce a type of highly modified cis-1,4 polyisoprene with a wide range of 2-MOPB content (8.2%–88.5%). The composition was adjusted by regulating the monomer feed ratio according to the copolymerization kinetics. Hydrogenation of P(2-MOPB) provided an unusual alternating copolymer, poly(4-methoxystyrene-alt-ethylene) that could not be obtained via any other methods.

Alkane elimination reaction of phosphinimino-amine ligand HL (L = (2,6-iPr2-C6H3)NC(Me)CHP(Cy2)N(2,6-Me2-C6H3)) with MgnBu2 and Sc(CH2SiMe3)3(THF)2, respectively, can afford the corresponding phosphinimino-amine supported magnesium monoalkyl complex LMgnBu(THF) (1) and scandium dialkyl complex LSc(CH2SiMe3)2 (2). 2 can initiate the polymerization of ethylene efficiently under the activation of [Ph3C][B(C6F5)4]. Magnesium hydride complex [LMgH]2 (3) can be easily obtained by the reaction of 1 and phenylsilane. The hydride species in 3 can conduct the dearomatisation of pyridine to give dearomatisation product 1,2-dihydropyridide (4).

(E)-1-(4-Methylphenyl)-1,3-butadiene (E-1-MPBD) synthesized via the “Wittig-type” reaction was polymerized with the ternary catalytic system (Flu-NHC)Lu(CH2SiMe3)2/AliBu3/[Ph3C][B(C6F5)4] (Flu-NHC = C13H8CH2CH2(NCHCHN(C6H2Me3-2,4,6)C) to afford a new product containing exclusively trans-3,4 (>99%) units with perfect syndiotacticity (rrrr > 99%). The regio-3,4 tacticity was proved by the IR and NMR (1H and 13C) spectroscopic analyses, while the 3,4-stereotacticity was confirmed by a model polymer with lower regularity (3,4 = 90.9%, rrrr = 49.3%) prepared by the binary catalytic system (Am-NHC)Lu(CH2SiMe3)2/[Ph3C][B(C6F5)4] (Am-NHC = 2,6-iPrC6H3N═C(C6H5)NCH2CH2(NCHCHN(C6H2Me3-2,4,6)C). The trans-planar conformation was uncovered through 2D-NOESY and 13C CPMAS NMR technologies. This represents the first stereo 3,4-syndioselective polymerization of 1,3-dienes achieved by a rare-earth metal based catalyst. Moreover, hydrogenating the resulting polymer gave the highly syndiotactic poly(4-methylphenyl-1-butene),...

Stereoselective coordination/insertion polymerization of the polar ortho-methoxystyrene has been achieved for the first time by using the cationic beta-diketiminato rare-earth-metal species. High activity and excellent isoselectivity (mmmm>99%) were acheived. The unmasked Lewis-basic methoxy group does not poison the Lewis-acidic metal center, but instead activates the polymerization through sigma-pi chelation to the active species together with the vinyl group, thus lower the coordination and activation energies as compared with those of styrene derivatives lacking the methoxy group.

Heterocyclic-fused cyclopentadienyl scandium bis(alkyl) complexes L1-4Sc(CH2SiMe3)(2)THF ((5-Me-1-Ph-cyclopenta[b]pyrrol-4-yl)Sc(CH2SiMe3)(2)THF (1), (2,5-Me-2-3-Ph-6H-cyclopenta[b]thiophenyl)Sc(CH2SiMe3)(2)THF (2), (2,4,5,6-Me-4-4H-cyclopenta[b]thiophenyl)Sc(CH2SiMe3)(2)THF (3), (2,3,4,5,6-Me-5-4H-cyclopenta[b]thiophenyl)Sc(CH2SiMe3)(2)THF) (4)) were facilely synthesized by alkane elimination reaction of Sc(CH2SiMe3)3(THF)2 with the heterocyclic-fused cyclopentadienyl ligands HL1-4 in high yields. Complexes 1-4 were characterized by H-1 and C-13 NMR spectroscopies and X-ray diffraction analyses as THF-solvated monomers, adopting a half-sandwich geometry. Upon activation of [Ph3C][B(C6F5)(4)]/AliBu(3), these half-sandwich scandium complexes displayed various activities toward the copolymerization of ethylene (E) and dicyclopentadiene (DCPD). Complex 1, supported by the phenyl-substituted pyrrole-fused cyclopentadienyl ligand, showed a slightly higher activity than the phenyl-substituted thiophene-fused cyclopentadienyl complex 2. Among the thiophene-fused cyclopentadienyl complexes 2-4, 4, bearing pentamethyl substituents, showed the highest activity of 2.9 x 10 (6) g/molSc.h.bar. The resultant copolymers had adjustable DCPD incorporation varying from 14.0 up to 46.1 mol %, of which the alternating poly(E-alt-DCPD) had a high Tg of 166 degrees C. In addition, no cross-linking was observed in the copolymers, suggesting that these catalytic systems were highly regioselective for the two active double bonds within DCPD.

Treatment of imidazolium iodide [R-NHC-CH2CH(nBu)OH]I (1a (R = methyl), 1b (R = isopropyl)) and benzimidazole iodide [R-NHC(C6H4)-CH2CH(nBu)OH]I (2a (R = methyl), 2b (R = isopropyl)), respectively, with ((trimethylsilyl)methyl)lithium (LiCH2SiMe3) followed by rare-earth metal tris(alkyl)s (Ln(CH2SiMe3)3(THF)2) (Ln = Sc, Y, Lu) afforded the alkoxy-modified N-heterocyclic carbene ligated rare-earth metal bis(alkyl) complexes {[R-NHC-CH2CH(nBu)OLn(CH2SiMe3)2]2 (3a (R = methyl, Ln = Sc), 3b (R = methyl, Ln = Lu), 4a (R = isopropyl, Ln = Y), 4b (R = isopropyl, Ln = Lu)) and [(CH3)2CH-NHC(C6H4)-CH2CH(nBu)OY(CH2SiMe3)2]2 (5)} via double-deprotonation reactions. All complexes were characterized by NMR spectroscopy, elemental analysis and X-ray crystallography. They are dimers in which two rare-earth metal ions are bridged by two μ2-O atoms. Under the activation of an organoborate, complex 3a showed cis-1,4 enriched regioselectivity for isoprene polymerization (84.3%).

A highly efficient strategy for synthesizing hydroxyl-end and amide-core, highly stereoregular, star-shaped polylactide was established by employing a lutetium complex via immortal ROP of rac-lactide with a polyamine as the chain transfer agent.

Introducing ethylene units into polybutadiene backbones is an approach to synthesize advanced rubber materials, which has been a research challenge because of distinct polymerization mechanisms of the two monomers. To date, only trans-1,4- and 1,2-regulated copolymers have been obtained. Herein, we reported the unprecedented cis-1,4 selective copolymerization of ethylene and butadiene by using the thiophene-fused cyclopentadienyl-ligated scandium complexes. The effects of the sterics and electronics of the catalytic precursors as well as the monomer loading mode on the activity and selectivity as well as the sequence lengths were investigated, and the mechanism was elucidated. Thus a novel ethylene-based rubber material possessing a high molecular weight, 80 % cis-1,4 regularity and a Tg=−94 °C without an obvious melting point owing to short polyethylene sequences even at its content up to 45 mol %, was isolated. This new rubber material exhibited excellent anti-flowing performance and strong tensile strength.

Precisely controlling the stereochemistry of a copolymerization by single catalyst, and achieving copolymers with predicted sequences, is a challenging project in organometallic and macromolecular sciences. This article reports that the copolymerization of isoprene and butadiene with the 3,4- and cis-1,4 different regioselectivities has been accessed through employing a pyridylmethylene functionalized fluorenyl ligated yttrium cationic species. The thus unprecedented regularity combination is attributed mainly to the backbiting interaction of the penultimate unit of the polymer chain to the active central metal ion according to the DFT calculation. Moreover, the compositions can be adjusted by regulating the monomer feed ratio according to the copolymerization kinetics study.

A series of aluminum complexes LaAl2Me4 (1), Lb2Al4Me4 (2), and LcAl2Me4 (3) have been prepared from the reaction of AlMe3 with Salan- and Salen-type ligands (LaH2 = [2-OH-3,5-tBu2-C6H2CH2N(CH3)]2-(m-phenylene); LbH4 = [2-OH-3,5-tBu2-C6H2CH2NH]2-(m-phenylene); LcH2 = [2-OH-3,5-tBu2-C6H2CH═N]2-(m-phenylene)), respectively. All these complexes were characterized by NMR spectroscopy, X-ray diffraction, and elemental analyses, with complexes 1 and 3 adopting binuclear structures, while complex 2 being tetranuclear. In the presence of alcohol, the binuclear complexes 1 and 3 catalyzed controlled ring-opening homopolymerizations of both e-CL and l-LA. In the copolymerization experiments, complexes 1 and 2 produced tapered copolymers of e-CL and l-LA, while complex 3 was able to provide e-CL-co-l-LA with tendentially random structure indicated by the average lengths of the caproyl and lactidyl sequences (LCL = 1.4; LLA = 2.6). Particularly, addition of excess alcohol into the catalytic system of complex 3 establ...

the first four-coordinate methanediide/alkyl lutetium complex (boddi) lu-2(ch2sime3)(2)(mu(2)-chsime3)(thf)(2) (boddi=arnc(me) chcochc(me) nar, ar=2,6-ipr(2)c(6)h(3)) (1) was synthesized by a thermolysis methodology through a-h abstraction from a lu-ch2sime3 group. complex 1 reacted with equimolar(2),6-iprc(6)h(3)nh(2) and ph2c=o to give the corresponding lutetium bridging imido and oxo complexes (boddi) lu-2(ch2sime3)(2)(mu(2)-n-2,6-ipr(2)c(6)h(3))(thf)(2) (2) and (boddi) lu-2(ch2sime3)(2)(mu(2)-o)(thf)(2) (3). treatment of 3 with ph2c=o (4 equiv) caused a rare insertion of lu-mu(2)-o bond into the c=o group to afford a diphenylmethyl diolate complex 4. reaction of 1 with phn=c=o (2 equiv) led to the migration of sime3 to the amido nitrogen atom to give complex (boddi) lu-2(ch2sime3)(2)-mu-{phnc(o)chc(o)nph(sime3)kappa n-3,o,o}(thf) (5). reaction of 1 with tbun equivalent to c formed an unprecedented product (boddi) lu-2(ch2sime3){mu(2)-[eta(2):eta(2)-tbunc(=ch2) sime2chc=ntbu-k 1n]}(tbun equivalent to c)(2) (6) through a cascade reaction of n equivalent to c bond insertion, sequential cyclometalative gamma-(sp(3))-h activation, c equivalent to c bond formation, and rearrangement of the newly formed carbene intermediate. the possible mechanistic pathways between 1, phn=c=o, and tbun equivalent to c were elucidated by dft calculations.

A highly efficient strategy for synthesizing the first biocompatible polyesters with AIE characteristics has been established via immortal ring-opening polymerizations of cyclic esters bearing nonluminophores. In the process, the large excess hydroxyl-modified AIE active compound, acting as the chain transfer agent, attaches to the active rare-earth metal catalyst via the rapid-reversible exchange reaction to initiate the polymerization. Thus, more polyester chains appear to grow from one active metal species, and the AIE fragments are incorporated into the polymer chains at specific sites, in situ. The resultant polyesters have linear, block, or star-shaped microstructures mimicking those of the modified AIE compounds. The polymerization solutions can be directly fabricated to large-area thin solid films. The obtained PLA, for instance, emits fluorescence in water/THF mixtures owing to aggregation, the intensity of which is 2850-fold stronger than that in THF solution. This strategy avoids complicated pr...

The amidino-modified N-heterocyclic carbene ligated lutetium bis(alkyl) complex 1, (Am-NHC)Lu(CH2SiMe3)2, was synthesized by treatment of (AmH-NHC-H)Br ((2,6-iPrC6H3N═C(C6H5)NHCH2CH2(NCHCHN(C6H2Me3-2,4,6)CH)Br) with ((trimethylsilyl)methyl)lithium (LiCH2SiMe3) and lutetium tris(alkyls) (Lu(CH2SiMe3)3(THF)2) via double-deprotonation reactions and characterized by NMR spectroscopy and X-ray diffraction analysis. Under activation of an organoborate, complex 1 exhibited distinguished catalytic performance for the polymerization of isoprene with respect to high activity, 3,4-regioselectivity (99.3%), and livingness mode. In contrast to the systems reported to date, this system seemed not to be affected obviously by the polymerization temperature (0–80 °C), solvents, monomer-to-initiator ratios (500–5000), and type of organoborate. The resultant polymers have high glass-transition temperatures (38–48 °C) and moderate syndiotacticity (racemic enchainment triad rr 45%, pentad rrrr 20%). In addition, the living lu...

Deprotonation of m-phenylene-bridged bis(β-diketiminate) ligands (PBDIiPr-H2 = [2,6-iPr2C6H3NHC(Me)C(H)C(Me)N]2-(m-phenylene); PBDIEt-H2 = [2,6-Et2C6H3NHC(Me)C(H)C(Me)N]2-(m-phenylene); PBDIMe-H2 = [2,6-Me2C6H3NHC(Me)C(H)C(Me)N]2-(m-phenylene)) by rare-earth-metal tris(alkyls) Ln(CH2SiMe3)3(THF)2 (Ln = Y, Lu, Sc) gave a series of rare-earth-metal bis(alkyl) complexes: PBDIiPr-[Y(CH2SiMe3)2]2(THF)2 (1), PBDIEt-[Ln(CH2SiMe3)2]2(THF)n (2a, Ln = Y, n = 2; 2b, Ln = Lu, n = 2; 2c, Ln = Sc, n = 1), and PBDIMe-[Y(CH2SiMe3)2]2(THF)2 (3). All these complexes were fully characterized by NMR spectroscopy, X-ray diffraction, and elemental analyses, adopting binuclear structures with the two rare-earth-metal ions taking trans positions versus the phenyl ring. Complexes 1, 2a,b, and 3 coordinate two solvated THF molecules, while the scandium complex 2c incorporates only one THF molecule, owing to the steric crowding. Upon activation with 2 equiv of organoborate, the yttrium systems showed higher catalytic activity towar...

The small substitution of Ti for Zr in the Co 80 Zr 18 B 2 melt-spun ribbons resulted in a significant improvement of magnetic properties. The optimal magnetic properties of coercivity Hc = 4.5 kOe, and maximum energy product ( BH ) max = 5.0 MGOe were obtained in the Co 80 Zr 15 Ti 3 B 2 ribbons produced at a wheel speed of 30 m/s. X-ray diffraction (XRD) and thermomagnetic analysis (TMA) revealed that the Co–Zr–Ti–B ribbons mainly consisted of Co 11 Zr 2 phase and Ti substitution made the phase more unstable. The investigation of microstructure indicated that the grain size decreased significantly with the increase of Ti content. A suitable grain size of Co 11 Zr 2 phase was believed to be the main reason for the drastic increase in coercivity. On the other hand, the appropriate refinement of grain led to a significant enhancement of intergrain exchange interaction in the Co 80 Zr 15 Ti 3 B 2 .

Rare-earth metal bis(alkyl) complexes (Flu–NHC)Ln(CH2SiMe3)2 (Ln = Dy (1), Er (2), Sc (3)) attached by fluorenyl-modified N-heterocyclic carbene ligands ((Flu H–NHC–H)Br) have been synthesized by treatment of (FluH–NHC–H)Br with (trimethylsilylmethyl)lithium (LiCH2SiMe3) and rare-earth metal tris(alkyl)s (Ln(CH2SiMe3)3(THF)2) via double-deprotonation reactions in moderate to high yields. Under mild conditions (40 °C and normal ethylene pressure), the scandium precursor 3, upon activation of AliBu3 and [Ph3C][B(C6F5)4], showed high activity (4120 kg molSc–1 h–1 atm–1) for the copolymerization of ethylene and 1-hexene with moderate 1-hexene insertion ratio (20.2%), although the analogous complexes 1 and 2 were inert. In addition, this system displayed excellent catalytic performances for the copolymerization of ethylene and a higher α-olefin 1-octene with an activity of up to 3640 kg molSc–1 h–1 atm–1. The content of 1-octene could be controlled swiftly from 2.1% to 38.7% by varying the 1-octene feed ratio....

The phases, microstructure, and magnetic properties of Co80Zr18−xNbxB2 (x=1, 2, 3, and 4) melt-spun ribbons were investigated. The small substitution of Nb for Zr in the Co–Zr–B melt-spun ribbons resulted in the improvement of magnetic properties, especially the coercivity. The main effect of added Nb on the coercovity of Co–Zr–Nb–B melt-spun ribbons, originated from modification of the grain size of Co11Zr2 phase. The coercivity of the Co–Zr–Nb–B melt-spun ribbons depends on the annealing temperature. The optimal magnetic properties of Hc=5.1 kOe, and (BH)max=3.4 MGOe were obtained in the Co80Zr15Nb3B2 melt-spun ribbons annealed at 600 °C for 3 min.

The phases and magnetic properties of Co–Zr–Ti melt-spun ribbons were studied by XRD analysis and magnetic measurements. The optimal magnetic properties of Ms=59.0 emu/g, Mr=4.0 kG, Hc=2.9 kOe, and (BH)max=3.0 MGOe were obtained in Co82Zr14Ti4 ribbons produced at a wheel speed of 30 m/s. In this work, we found that Ti was one of the few large atomic radius elements, which could improve hard magnetic properties of Co–Zr alloy.

Co80Zr18−xMoxB2 (x=1, 2, 3, 4) alloys have been produced by melt-spinning followed by heat treatment. We get a high coercivity of 6.3 kOe for the sample with x=2. Heat treatment of Co–Zr–Mo–B melt-spun ribbons results in an increase in coercivity. Co80Zr16Mo2B2 ribbons, annealed at 600 °C for 30 min, exhibit the optimized magnetic properties of Hc=6.8 kOe, σr=37.14 emu/g and (BH)max=2.85 MGOe. The hysteresis curves of the studied ribbons are very smooth and their ratios σr/σs exceed 0.6.

Single-molecule magnets are compounds that exhibit magnetic bistability purely of molecular origin. The control of anisotropy and suppression of quantum tunneling to obtain a comprehensive picture of the relaxation pathway manifold, is of utmost importance with the ultimate goal of slowing the relaxation dynamics within single-molecule magnets to facilitate their potential applications. Combined ab initio calculations and detailed magnetization dynamics studies reveal the unprecedented relaxation mediated via the second excited state within a new DyNCN system comprising a valence-localized carbon coordinated to a single dysprosium(III) ion. The essentially C2v symmetry of the Dy(III) ion results in a new relaxation mechanism, hitherto unknown for mononuclear Dy(III) complexes, opening new perspectives for means of enhancing the anisotropy contribution to the spin-relaxation barrier.

A red blood cell antigen polymorphism was demonstrated in red crucian carp with a series of serological procedures including isohaemagglutination, absorption of isosera and heteroimmune sera. This antigen system, named the S system, contained two dominant antigen factors, ''S1'' and ''S2'' as well as a null factor, ''SO''. Individuals tested had either one or two, or neither of the antigens, with the expression of four phenotypes, S1, S1S2, S2 and S0. The hybridological analyses between proposed phenotypes indicated that the genetic background for this system can be explained by a simple hypothesis based on three alleles, designated S1, S2 and S0, in one locus.

The chromosomes of the artificial triploid carp consist of three complete genomes from Xingguo red carp (Cyprinus carpio), mirror carp (Cyprinus carpio) and red crucian carp (Carassius auratus). Starch and polyacrylamide gel analysis reveals that some SOD and s-MDH alleles of red crucian carp are undetectable in tissues of the artificial multiple triploid carp. It was found that the majority of oocytes of female artificial multiple triploid carp (XXX) developed to maturity, but spermatocytes of the male (XXY) developed abnormally and no spermatozoa were found. The external features of the triploid carp egg are quite different from those of normal diploid eggs. Sections of fertilized eggs reveal that the majority of eggs are polyspermous. Irradiated sperm was used to induce the gynogenesis of the artificial multiple triploid carp eggs. The eggs cleaved and developed normally, but the numbers of chromosomes of gastrular cells were variable, i.e., 50, 75, 100 and 150. This suggests that the behavior of the chromosomes in meiosis is polytypic, and some female nuclei of the eggs remain triploid after activation. All viable offspring of gynogenetic artificial multiple triploid carp are triploid and no segregation was found in their appearances, scale-covering type and body coloration.

By using the dielectric description theory of ionicity of solids, chemical bond properties of rare earth ions with various ligands are studied. Calculated results show that chemical bond properties of the same rare earth ion and the same ligand in different crystals depend on the crystal structures. In a series of compounds, chemical bond properties of crystals containing different rare earth ions are similar. The magnitude of covalency of chemical bonds of trivalent rare earth ions and various ligands has an order like F