Polymerization of 2,2 '-Dimethyltrimethylene Carbonate by Lutetium Complexes Bearing Amino-Phosphine Ligands

A series of lutetium alkyl, amino, and guanidinato complexes based upon an amino-phosphine ligand framework had been prepared. These complexes were applied to initiate ring-opening polymerization of 2,2'-dimethyltrimethylene carbonate (DTC). The type of the initiator significantly influenced the catalytic activity of these complexes in a trend as follows: alkyl approximate to guanidinate > amide, whereas the complexes with flexible backbone between P and N atoms within the ligand exhibited higher activity than those with rigid backbone. The isolated PDTC had bimodal-mode molecular weight distribution. The molecular weights of each fraction increased linearly with the conversion, indicating that there might be two active species. This had been confirmed by analyses of oligomeric DTC living species and oligomer with NMR technique as the metal-alkoxide and the four-membered metallocyclic lactate. Kinetic investigation displayed that the polymerization rate was the first order with the monomer concentration.

Highly Active Neutral Nickel(II) Catalysts for Ethylene Polymerization Bearing Modified,beta-Ketoiminato Ligands

A series of novel neutral nickel complexes 4a-e bearing modified beta-ketoiminato ligands [(2,6-(Pr2C6H3)-Pr-i)N=C(R-1)CHC(2 '-R2C6H4)O]Ni(Ph)(PPh3) (4a, R-1 R-2 = H; 4b, R-1 = H, R-2 = Ph; 4c, R-1 = H, R-2 = Naphth; 4d, R-1 = CH3, R-2 = Ph; 4e, R-1 = CF3, R-2 Ph) have been synthesized and characterized. Molecular structures of 4b and 4e were further confirmed by X-ray crystallographic analysis. Activated with B(C6F5)(3), all the complexes are active for the polymerization of ethylene to branched polyethylenes. Ligand structure, i.e., substituents R-1 and R-2, greatly influences not only catalytic activity but also the molecular weight and branch content of the polyethylene produced. The phenyl-substituted complex 4b exhibits the highest activity of lip to 145 kg PE/mol(Ni)center dot h center dot atm under optimized conditions, which is about 10 times more than unsubstituted complex 4a (14.0 kg PE/mol(Ni center dot)h center dot atm). Highly branched polyethylene with 103 branches per 1000 carbon atoms has been prepared using catalyst 4e.

Ethylene Polymerization and Ethylene/Hexene Copolymerization with Vanadium(III) Catalysts Bearing Heteroatom-Containing Salicylaldiminato Ligands

A series of novel vanadium(III) complexes hearing heteroatoill-containing group-substituted salicylaldiminato ligands [RN=CH(ArO)]VCl2(THF)(2) (Ar = C6H4, R = C3H2NS, 2a; C7H4NS, 2c; C7H5N2, 2d; Ar = C(6)H(2)tBu(2) (2,4), R = C3H2NS, 2b) have been synthesized and characterized. Structure of complex 2c was further confirmed by X-ray crystallographic analysis. The complexes were investigated as the catalysts for ethylene polymerization in the presence of Et2AlCl. Complexes 2a-d exhibited high catalytic activities (up to 22.8 kg polyethylene/mmolv h bar), and affording polymer with unimodal molecular weight distributions at 25-70 degrees C in the first 5-min polymerization, whereas produced bimodal molecular weight distribution polymers at 70 degrees C when polymerization time prolonged to 30 min. The catalyst structure plays an important role in controlling the molecular weight and molecular weight distribution of the resultant polymers produced in 30 min polymerization. In addition, ethylene/hexene copolymerizations with catalysts 2a-d were also explored in the presence of Et2AlCl, which leads to the high molecular weight and unimodal distributions copolymers with high comonomer incorporation.

Synthesis and characterization of the titanium complexes bearing two regioisomeric trifluoromethyl-containing enaminoketonato ligands and their behavior in ethylene polymerization

A series of new titanium complexes bearing two regioisomeric trifluoromethyl-containing enaminoketonato ligands (3a-h and 6a-h), [PhN=CRCHC(CF3)O](2)TiCl2 (3a, R = Me; 3b, R = n-C5H11; 3c, R = i-Pr; 3d, R = Cy; 3e, R = t-Bu; 3f, R = CH=CHPh; 3g, R = Et; 3h, R = n-C11H23) and [PhN=C(CF3)CHC(R)O](2)TiCl2 (6a, R = Ph; 6b, R = n-C5H11; 6c, R = i-Pr; 6d, R = Cy; 6e, R = t-Bu; 6f, R = CH=CHPh; 6g, R = CHPh2; 6h, R = CF3) have been synthesized and characterized. X-ray crystal structures analyses suggest that complexes 3c-e and 6c-d all adopt a distorted octahedral geometry around the titanium center. Complexes 3c, 3d and 6c display a cis-configuration of the two chlorine atoms around the titanium center, while complex 6d shows a trans-configuration of the two chlorine atoms. Especially, the configurational isomers (cis and trans) of complex 3e were identified both in solution and in the solid state by NMR and X-ray analyses. With modified methylaluminoxane as a cocatalyst, all the complexes are active towards ethylene polymerization, and produce high molecular weight polymers.

Rare earth metal alkyl complexes bearing N,O,P multidentate ligands: Synthesis, characterization and catalysis on the ring-opening polymerization of L-lactide

Alkane elimination reactions of rare earth metal tris(alkyl)s, Ln(CH2SiMe3)3(THF)2 (Ln = Y, Lu) with the multidentate ligands HL1-4, afforded a series of new rare earth metal complexes. Yttrium, complex I supported by flexible amino-intino phenoxide ligand HL1 was isolated as homoleptic product. In the reaction of rigid phosphino-imino phenoxide ligand HL 2 with equintolar Ln(CH2SiMe3)3(THF)2, HL 2 was deprotonated by the metal alkyl and its imino C=N group was reduced to C-N by intramolecular alkylation, generating THF-solvated mono-alkyl complexes (2a: Ln = Y; 2b: Ln = Lu). The di-ligand chelated yttriurn complex 3 without alkyl moiety was isolated when the molar ratio of HL 2 to Y(CH,SiMe3)3(THF)2 increased to 2: 1. Reaction of steric phosphino beta-ketoiminato ligand HL 3 with equimolar Ln(CH2SiMe3)3(THF)2 afforded di-ligated mono-alkyl complexes (4a: Ln = Y; 4b: Ln = Lu) without occurrence of intramolecular alkylation or formation of homoleptic product. Treatment of tetradentate methoxy-amino phenol HL 4 with Y(CH2SiMe3)3(THF)2 afforded a monomeric yttrium bis-alkyl complex of THF-free. The resultant complexes were characterized by IR, NMR spectrum and X-ray diffraction analyses.All alkyl complexes exhibited high activity toward the ring-opening polymerization Of L-lactide to give isotactic polylactide with controllable molecular weight and narrow to moderate polydispersity.

Synthesis, structure and norbornene polymerization behavior of nickel complexes bearing two beta-ketoiminato chelate ligands

A series of nickel(II) complexes bearing two nonsymmetric bidentate beta-ketoiminato chelate ligands have been prepared, and the structures of complexes [(2,6-Me2C6H3)NC(CH3)C(H)C(Ph)O](2)Ni (4a) and [(2,6-Me2C6H3)NC(CH3)C(H)C(CF3)O](2)Ni (4c) have been confirmed by X-ray crystallographic analysis. These nickel(II) complexes were investigated as catalysts for the vinylic polymerization of norbornene. Using modified methylaluminoxane (MMAO) as a cocatalyst, these complexes display very high activities and produce high molecular weight polymers. Catalytic activity of up to 1.16 x 10(4) kg/mol(Ni) .h and the viscosity-average molecular 9 weight of polymer of up to 870 kg/mol were observed. Catalyst activity, polymer yield, and polymer molecular weight could be controlled over a wide range by the variation of the reaction parameters such as Al/Ni molar ratio, norbornene/catalyst molar ratio, monomer concentration, polymerization reaction temperature and time.

Self-immobilized metallocene catalysts bearing an allyl group for ethylene polymerization, X-ray crystal structure of [(CH2=CHCH2)CH3Si(C13H8)(2)]ZrCl2

A series of ansa-metallocene complexes with an allyl substituted silane bridge [(CH =CHCH2)CH3Si(C5H4)(2)]TiCl2 (1), [(CH2=CHCH2)CH3Si(C9H6)(2)]MCl2 [M = Ti (2), Zr (3), Hf (4)] and [(CH2=CHCH2)CH3Si(C13H8)(2)]ZrCl2 (6) have been synthesized and characterized. The molecular structure of 6 has been determined by X-ray crystallographic analysis. Complexes 1-4, 6 bearing allyl groups have been investigated as self-immobilized catalysts for ethylene polymerization in the presence of MMAO. The results showed that the self-immobilized catalysts 1-4, 6 kept high ethylene polymerization activities of ca. 10(6) g PE mol(-1) M h(-1) and high molecular weight (M-w approximate to 10(5)) of polyethylene.

Biodegradable amphiphilic triblock copolymer bearing pendant glucose residues: Preparation and specific interaction with Concanavalin A molecules

A novel biodegradable amphiphilic block copolymer PLGG-PEG-PLGG bearing pendant glucose residues is successfully prepared by the coupling reaction of 3-(2-aminoethylthio) propyl-R-D-glucopyranoside with the pendant carboxyl groups of PLGG-PEG-PLGG in the presence of N,N'-carbonyldiimidazole. The polymer PLGG-PEG-PLGG, i.e., poly {(lactic acid)-co-[(glycolic acid)-alt-(L-glutamic acid)]}-block-poly(ethylene glycol)-block-poly{( lactic acid)-co-[( glycolic acid)-alt-(L-glutamic acid)]}, is prepared by ring-opening copolymerization of L-lactide (LLA) with (3s)-benzoxylcarbonylethylmorpholine-2,5-dione (BEMD) in the presence of dihydroxyl PEG with molecular weight of 2000 as macroinitiator and Sn(Oct)(2) as catalyst, and then by catalytic hydrogenation. The glucose-grafted copolymer shows a lower degree of cytotoxicity to ECV-304 cells and improved specific recognition and binding with Concanavalin A (Con A). Therefore, this kind of glucose-grafted copolymer may find biomedical applications.

New neutral nickel(II) complexes bearing pyrrole-imine chelate ligands: synthesis, structure and norbornene polymerization behavior

New neutral nickel(II) complexes bearing nonsymmetric bidentate pyrrole-imine chelate ligands (4a-d), [2-(ArNCH)C4H3N]Ni(PPh3)Ph [Ar=2,6-diisopropylphenyl (a), 2-methyl-6-isopropylphenyl (b), 2,6-diethylphenyl (c), 2-tert-butylphenyl (d)], have been prepared in good yields from the sodium salts of the corresponding ligands and trans-Ni(PPh3)(2)(Ph)Cl, and the structure of complex 4a has been confirmed by X-ray crystallographic analysis. These neutral Ni(II) complexes were investigated as catalysts for the vinylic polymerization of norbornene. Using modified methylaluminoxane (MMAO) as a cocatalyst, these complexes display very high activities and produce great mass polymers. Catalyst activity of up to 4.2 x 10(7) g (mol Ni h)(-1) and the viscosity-average molecular weight of polymer of up to 9.2 x 10(5) g mol(-1) were observed. Catalyst activity, polymer yield, and polymer molecular weight can be controlled over a wide range by the variation of reaction parameters such as Al-Ni ratio, norbornene-catalyst ratio, monomer concentration, polymerization reaction temperature and time.

Ethylene polymerization by self-immobilized neutral nickel catalysts bearing allyl groups

[Ni(Ph)(PPh3)(N,O)] complexes containing phenyliminophenolato ligands (N,O) (1: N,O = A; 2: N,O = B; 3: N,O = Q 4: N,O = D; 5: N,O = E) have been synthesized and characterized. The molecular structure of 4 was determined by single-crystal X-ray analysis. Complexes 2-5 bearing allyl groups have been investigated as self-immobilized catalysts for ethylene polymerization without the use of co-catalysts. The high ethylene polymerization activities of ca. 10(5) g.PE mol(-1) Ni.h(-1) and high molecular weight (M-w approximate to 10(5)) of polyethylene could be accomplished by changing the ligand structures and reaction conditions. The self-immobilization of catalysts brings about a dramatic increase in the catalytic activities of ethylene polymerization.

The Stability of a Vertical Single-Walled Carbon Nanotube Under Its Own Weight

It has been reported recently that single carbon nanotubes were attached to AFM tips to act as nanotweezers. In order to investigate its stability, a vertical single-walled carbon nanotube (SWCNT) under its own weight is studied in this paper. The lower end of the carbon nanotube is clamped. Firstly the governing dimensionless numbers are derived by dimensional analysis. Then the theoretical analysis based on an elastic column model is carried out. Two ratios, I.e., the ratio of half wall thickness to radius (t=R) and the ratio of gravity to elastic resilience ($\rho$gR=E), and their influences on the ratio of critical length to radius are discussed. It is found that the relationship between the critical ratio of altitude to radius and ratio of half thickness to radius is approximately linear. As the dimensionless number $\rho$gR=E increases, the compressive force per unit length (weight) becomes larger, thus critical ratio of altitude to radius must become smaller to maintain stability. At last the critical length of SWCNT is calculated. The results of this paper will be helpful for the stability design of nanotweezers-like nanostructures.

Semi-weight function method on computation of stress intensity factors in dissimilar materials

Semi-weight function method is developed to solve the plane problem of two bonded dissimilar materials containing a crack along the bond. From equilibrium equation, stress and strain relationship, conditions of continuity across interface and free crack surface, the stress and displacement fields were obtained. The eigenvalue of these fields is lambda. Semi-weight functions were obtained as virtual displacement and stress fields with eigenvalue-lambda. Integral expression of fracture parameters, K-I and K-II, were obtained from reciprocal work theorem with semi-weight functions and approximate displacement and stress values on any integral path around crack tip. The calculation results of applications show that the semi-weight function method is a simple, convenient and high precision calculation method.

A Study of the Tribological Behavior of Carbon-Nanotube-Reinforced Ultrahigh Molecular Weight Polyethylene Composites

The tribological properties of the high-strength and high-modulus ultrahigh molecular weight polyethylene (UHMWPE) film and the UHMWPE composites reinforced by multiwalled carbon nanotubes (MWCNT/UHMWPE) were investigated using a nanoindenter and atomic force microscope (AFM). The MWCNT/UHMWPE composites films exhibited not only high wear resistance but also a low friction coefficient compared to the pure UHMWPE films. We attribute the high wear resistance to the formation of the new microstructure in the composites due to the addition of MWCNTs.

Research on Bearing Capacity Calculation Method of Large Diameter Cylinder in Soft Clay

A large diameter cylinder inserted in soils is a new type of engineering structures used in offshore and port engineering. The mechanism of its bearing capacity and the analysis of its stability are important to its design and applications. In this paper, the finite element method is used to analyze the reacting forces of the soft soil foundation on the structure under the wave action. A simplified method is proposed, based on the plastic limit method, for the safety and stability analysis. Our analysis shows that the assumptions made in this paper and the mechanism used are reasonable, and the results obtained are appropriate. The calculation method is very efficient and can be used to evaluate main parameters of the structure in its preliminary designs.