Synthesis,characterization, and catalytic application of a zinc(II) complex bearing a pyrazole-based ligand

The reaction between ZnCl₂ and N,N-bis[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]-1-phenylethylamine (bdmppea) affords [(bdmppea)ZnCl₂], whose structure has been determined by X-ray crystallography. The [(bdmppea)ZnEt₂] complex in situ prepared by the reaction between [bdmppea] and ZnEt₂ exhibited high activity toward the polymerization reaction of rac-lactide at room temperature. However, its activity decreased sharply with decreasing temperature. Stereospecificity of this catalyst characterized by heterotacticity (P_r) was determined by homonuclear decoupled NMR spectroscopy, which value was ∼0.58.     

Viscoelasticity and thermal stability of polylactide composites with various functionalized carbon nanotubes

Polylactide (PLA) nanocomposites containing various functionalized multi-walled carbon nanotubes (MWCNTs) were prepared directly by melt compounding. The linear rheology and thermal stability of the PLA nanocomposites were, respectively, investigated by the parallel plate rheometer and TGA, aiming at examining the effect of surface functionalization on the dispersion of MWCNTs by using viscoelastic and thermal properties. Among three MWCNTs used in this work, the carboxylic MWCNTs present better dispersion in PLA matrix than the hydroxy and purified MWCNTs because the corresponding composite shows the lowest rheological percolation threshold, which is further confirmed by the TEM and solution experiments. The presence of all these three MWCNTs, however, nearly cannot improve the thermal stability effectively at the initial stage of degradation and the temperature corresponding to a weight loss of 5 wt% (T_5 wt%) only shows slight increase in contrast to that of the neat PLA while with increase of decomposition level, the presence of carboxylic and purified MWCNTs retards the depolymerization of PLA evidently, showing remarkable increase in the temperature corresponding to maximum rate of decomposition (T_max). Both the dispersion state and the surface functionalization of MWCNTs are very important to the thermal stability of PLA matrix.     

Synthesis and characterization of phosphorous-bridged bisphenoxy titanium complexes and their application to ethylene polymerization

Phosphorous-bridged bisphenoxy titanium complexes were synthesized and their ethylene polymerization behavior was investigated. Bis[3-tert-butyl-5-methyl-2-phenoxy](phenyl)phosphine tetrahydrofuran titanium dichloride (4a) was obtained by treatment of 3 equiv of n-BuLi with bis[3-tert-butyl-2-hydroxy-5-methylphenyl](phenyl)phosphine hydrochloride salt (3a) followed by TiCl₄(THF)₂ in THF. THF-free complexes 5a-5d were synthesized more conveniently by the direct reaction of MOM-protected ligands (2a-2d) with TiCl₄ in toluene. X-ray analysis of 4a revealed that the ligand is bonded to the octahedral titanium (IV) center in a facial fashion and two chlorine atoms possess cis-geometry. Complexes 4a and 5a-5d were utilized as catalyst precursors for ethylene polymerization. Complex 5c gave high molecular weight polyethylene (M_w = 1,170,000, M_w/M_n = 2.0) upon activation with Al(ⁱBu)₃/[Ph₃C][B(C₆F₅)₄] (TB). Ethylene polymerization activity of 5d activated with Al(ⁱBu)₃/TB reached 49.0 × 10⁶ g mol (cat) ⁻¹ h⁻¹.     

Synthesis and characterization of complexes imparting N-pyridyl bonded meso-pyridyl substituted dipyrromethanes

The meso-pyridyl substituted dipyrromethane ligands 5-(4-pyridyl)dipyrromethane (4-dpmane) and 5-(3-pyridyl)dipyrromethane (3-dpmane) have been employed in the synthesis of a series of complexes with the general formulations [(η⁶-arene)RuCl₂(L)] (η⁶-arene = C₆H₆, C₁₀H₁₄) and [(η⁵-C₅Me₅)MCl₂(L)] (M = Rh, Ir). The reaction products have been characterized by microanalyses and spectral studies and molecular structures of the complexes [(η⁶-C₁₀H₁₄)RuCl₂(4-dpmane)] and [(η⁵-C₅Me₅)IrCl₂(3-dpmane)] have been determined crystallographically. For comparative studies, geometrical optimization have been performed on the complex [(η⁵-C₅Me₅)IrCl₂(4-dpmane)] using exchange correlation functional B3LYP. Optimized bond length and angles are in good agreement with the structural data of the complex [(η⁵-C₅Me₅)IrCl₂(3-dpmane)]. The complexes [(η⁶-C₁₀H₁₄)RuCl₂(3-dpmane)], [(η⁵-C₅Me₅)RhCl₂(3-dpmane)] and [(η⁵-C₅Me₅)IrCl₂(3-dpmane)] have been employed as a transfer hydrogenation catalyst in the reduction of aldehydes. It was observed that the rhodium and iridium complexes mentioned above are more effective in this regard in comparison to the ruthenium complex.     

Ageing of polylactide and polylactide nanocomposite filaments

An experimental study was carried out in order to check the influence of various parameters on the ageing of PLA filaments performed in a climatic room. Initially, two grades of PLA with different d-isomer contents were analysed. Even after several weeks of ageing, properties of PLA filaments with less than 0.5% d-isomer content did not vary extensively. On the other hand, the mechanical and thermal properties of PLA filaments with 4% d-isomer content underwent strong modifications. Subsequently, a selected organomodified bentonite (Bentone^®104 - noted as B104) was blended with PLA and then melt-spun to study the influence of a nanofiller on the ageing of PLA filaments. Faster degradation of PLA nanocomposite filaments was then observed.     

Rhodium or ruthenium units peripherally coordinated to carbosilane dendrimers functionalized with P-stereogenic monophosphines

Carbosilane dendrimers containing P-stereogenic monophosphines as terminal groups, Dend-{CH₂PPhR}_n (R = 2-biphenylyl or 9-phenanthryl), were reacted with [RhCl(COD)]₂ or [RuCl₂(p-cymene)]₂ to afford the corresponding chiral metalladendrimers Dend-{CH₂PPhR(RhCl(COD))}_n or Dend-{CH₂PPhR(RuCl₂(p-cymene))}_n, respectively. Attempts to obtain the first generation Ru-dendrimer for R = 2-biphenylyl proved unsuccessful, probably due to the steric hindrance of R. Complete characterization of these species was achieved by multinuclear NMR spectra, including 2D experiments, mass spectrometry, and optical rotation determinations. The catalytic properties of the rhodium dendrimers were tested in the hydrogenation of dimethylitaconate and those of the ruthenium derivatives in the asymmetric hydrogen transfer of acetophenone. The following model chiral compounds, (CH₃)₃Si{CH₂PPhR(RhCl(COD))} and (CH₃)₃Si{CH₂PPhR(RuCl₂(p-cymene))}, were prepared in order to detect potential dendritic effects. All compounds were active in the catalytic conditions tested, but low or null e.e. were found.     

取代聚炔的合成及其分离性能

具有优异物理和化学性能的新聚合物开发推动了取代聚炔的设计与合成。聚炔中功能侧基的引入赋予其非线性光学、液晶、发光、螺旋手性和高气体渗透等性能。作为一种重要的分离膜材料,与传统的玻璃态聚合物膜材料不同,这种无定形、高刚性的聚合物的显著特点是具有非常高的气体渗透系数和蒸汽／气体分离系数。有关其气体分离、天然气净化和对映体拆...     

Effect of compatibilizig agent on the properties of polylactide and polylactide based composite during ozone exposure

Compatibilizers belong to the most important internal factors which influence the degradation process of polymer matrix. For this reason in the current study, polylactide (L), polylactide with 5% of poly(ε-caprolactone) (LK) as compatibilizing agent and samples with 5%wt. of montmorillonite (MMT) (LS5 and LS5K respectively) before and after various time of ozone exposure have been analyzed. The results from infrared spectroscopy, gel permeation chromatography, atomic force microscopy, differential scanning calorimetry and thermogravimetric analysis have been presented. It has been established that microstructural changes during ozone exposure of the samples with the presence of compatibilizer increase in relation to the samples comprising PLA and PLA filled with montmorillonite. Moreover it has been determined that the introduction of poly(ε-caprolactone) into pure polymer as well as into PLA-montmorillonite material accelerates ozone-induced degradation, although it does not change the mechanism of the degradation process.     

Preparation and properties of two new soluble carbazole-containing functional polyacetylenes

Two new functional polyacetylenes bearing carbazole group as pendant,poly {3-[（4-ethynylstyryl）-N-butyl]carba/ole}（P1） and poly{3-[4-（prop-2-ynyloxy）phenyl-N-butyl]carbazole}（P2）,were prepared using[Rh（nbd）Cl)₂-Et₃N as catalyst.The polymers were soluble in common organic solvents such as CHCl₃ and THK Their structures and properties were characterized and evaluated with FTIR,¹H NMR,UV,TGA,GPC,and CV,respectively.The results show that the polymers possess high thermal stability and well hole-injection property.     

(1S, 2S)-DPEN修饰的负载型钌-铑双金属催化剂催化苯乙酮及其衍生物的不对称加氢

制备了以三苯基膦(PPh3)作为助剂的Ru-Rh/γ-Al2O3 催化剂, 在氢氧化钾的异丙醇溶液中, 用(1S, 2S)-DPEN [(1S, 2S)-1,2-diphenylethane-1,2-diamine]作手性修饰剂对苯乙酮及其衍生物进行不对称催化加氢, 此催化剂表现出较高的催化活性和良好的对映选择性. 优化反应条件, 苯乙酮、乙基苯基酮和异丙基苯基酮的转化率分别达到92.5%, 95.9%, 100%, 生成(R)-构型产物的ee值分别达到79.6%、81.2%和81.4%.     

New titanium and zirconium initiators for the production of polylactide

Two new group 4 initiators based on N,N′-Bis(2-hydroxybenzyl)ethylenediamine have been prepared and fully characterised via multi-nuclear NMR spectroscopy and single crystal X-ray diffraction studies. The complexes have been tested for the production of polylactide. The phenolate ligand complexes to Ti(IV) to generate the β-cis isomer in the solid-state. Whereas for Zr(IV) the isolated species (regardless of stoichiometery) is a diligated complex.     

Rheology and thermal stability of polylactide/clay nanocomposites

Polylactide/clay nanocomposites (PLACNs) were prepared by melt intercalation. The intercalated structure of PLACNs was investigated using XRD and TEM. Both the linear and nonlinear rheological properties of PLACNs were measured by parallel plate rheometer. The results reveal that percolation threshold of the PLACNs is about 4 wt%, and the network structure is very sensitive to both the quiescent and the large amplitude oscillatory shear (LAOS) deformation. The stress overshoots in the reverse flow experiments were strongly dependent on the rest time and shear rate but shows a strain-scaling response to the startup of steady shear flow, indicating that the formation of the long-range structure in PLACNs may be the major driving force for the reorganization of the clay network. The thermal behavior of PLACNs was also characterized. However, the results show that with the addition of clay, the thermal stability of PLACNs decreases in contrast to that of pure PLA.     

Bulk and surface modifications of polylactide

This article reviews various methods of modifying the bulk and surface properties of poly(lactic acid) (PLA) so that the polymer may be used as a drug carrier in a drug delivery system (DDS) and as a cell scaffold in tissue engineering. Copolymerization of lactide with other lactone-type monomers or monomers with functional groups such as malic acid, copolymerization of lactide with macromolecular monomer such as poly(ethylene glycol) (PEG) or dextran, as well as blending polylactide and natural derivatives and other methods of bulk modification are discussed. Surface modifications of PLA-type copolymers, such as surface coating, chemical modification, and plasma treatment are described. Cell culture technology proves the efficiency of bulk and surface modification and the potential application of PLA in tissue engineering.     

Synthesis and degradation of end‐group‐functionalized polylactide

Three kinds of OH‐terminated polylactides were synthesized by the ring‐opening polymerization of lactide, with an alcohol such as dodecanol, glycerol, or pentaerythritol, in the presence of stannous octoate. Moreover, Cl‐, NH₂‐, and COOH‐terminated polylactides were synthesized from OH‐terminated polylactides. The end groups of the polylactides were identified by ¹H NMR and ¹³C NMR. According to thermal analysis, the cold crystallization temperatures of Cl‐, NH₂‐, and COOH‐terminated polylactides were higher than those of OH‐terminated polylactides. The thermal stability of OH‐terminated polylactides was poor, whereas NH₂‐ and Cl‐terminated polylactides were more resistant to thermal degradation. In a hydrolysis degradation test, the mass and molecular weight loss of COOH‐terminated polylactides were high, whereas those of Cl‐ and NH₂‐terminated polylactides were much lower. These end‐group effects were increased with an increasing number of chain arms. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 973–985, 2001     

Half-sandwich Ru(II), Ir(III) and Rh(III) complexes with bridging or chelating N-heterocyclic bis-carbene ligand: Synthesis and characterization

N-heterocyclic bis-carbene ligand (bis-NHC) which was derived from 1,1′-diisopropyl-3,3′-ethylenediimidazolium dibromide (L·2HBr) via silver carbene transfer method, reacted with [(η⁶-p-cymene)RuCl₂]₂ and [Cp^∗MCl₂]₂ (Cp^∗ = η⁵-C₅Me_5, M = Ir, Rh) respectively, afforded complexes [(η⁶-p-cymene)RuCl₂]₂(L) (1), [Cp^∗IrCl₂]₂(L) (2) and [Cp^∗RhCl(L)][Cp^∗RhCl₃] (3). When [Cp^∗IrCl₂]₂ was treated with 2 equiv AgOTf at first, and then reacted with bis-NHC ligand, [Cp^∗IrCl(L)]OTf (4) was obtained. The molecular structures of complexes 1-4 were determined by X-ray single crystal analysis, showing that 1 and 2 adopted bridging coordination mode, 3 and 4 adopted chelating coordination mode. All of these complexes were characterized by ¹H, ¹³C NMR spectroscopy and element analysis.     

Biodegradability of polylactide bottles in real and simulated composting conditions

As new biodegradable polymers and their packaging applications are emerging, there is a need to address their environmental performance. In particular, there is a need to understand the time required for their complete disintegration, before these materials are deployed in commercial composting processes. Standards developed by ASTM and ISO evaluate the biodegradation of biodegradable plastic materials in simulated controlled composting conditions. However, a more detailed understanding of the biodegradation of complete packages is needed in order to have a successful composting operation. This paper investigates the biodegradation performance of polylactide (PLA) bottles under simulated composting conditions according to ASTM and ISO standards, and these results are compared with a novel method of evaluating package biodegradation in real composting conditions. Two simulated composting methods were used in this study to assess biodegradability of PLA bottles: (a) a cumulative measurement respirometric (CMR) system and (b) a gravimetric measurement respirometric (GMR) system. Both CMR and GMR systems showed similar trends of biodegradation for PLA bottles and at the end of the 58th day the mineralization was 84.2±0.9% and 77.8±10.4%, respectively. PLA bottle biodegradation in real composting conditions was correlated to their breakdown and variation in molecular weight. Molecular weight of 4100 Da was obtained for PLA bottles in real composting conditions on the 30th day. The biodegradation observed for PLA bottles in both conditions explored in this study matches well with theoretical degradation and biodegradation mechanisms; however, biodegradation variability exists in both conditions and is discussed in this paper.     

可溶性聚对二乙炔苯的合成与表征

一些π-共轭高聚物由于具有优良的荧光性能或三阶非线性光学性能而引起了人们极大的兴趣,合成新型可溶性π-共轭高聚物的研究已成为近年来的研究热点.对二乙炔苯的聚合研究已有报道.     

Renewable resource-based composites of recycled natural fibers and maleated polylactide bioplastic: Characterization and biodegradability

The thermal properties of composite materials composed of polylactide (PLA) and green coconut fiber (GCF) were evaluated. Blends containing maleic anhydride-grafted PLA (PLA-g-MA/GCF) exhibited noticeably superior thermal properties due to greater compatibility between the two components. The dispersion of GCF in the PLA-g-MA matrix was highly homogeneous as a result of ester formation, and the consequent creation of branched and cross-linked macromolecules, between the carboxyl groups of PLA-g-MA and the hydroxyl groups in GCF. In addition, the PLA-g-MA/GCF blend was more easily processed due to a lower melt viscosity. Each composite was subject to biodegradation tests in a Burkholderia cepacia BCRC 14253 compost. The bacterium completely degraded both the PLA and the PLA-g-MA/GCF composite films. Morphological observations indicated severe disruption of the film structure after 9-12 days of incubation. The PLA-g-MA/GCF (10 wt%) films were not only more biodegradable than those made of PLA, but also exhibited lower molecular weight and intrinsic viscosity, implying a strong connection between these characteristics and biodegradability.     

Synthesis of unbridged metallocene catalyst for propylene polymerization

An unbridged metallocene catalyst bis(2,4,6-trimethylindenyl)zirconium dichloride (Cat-I) was synthesized. Propylene polymerization was carried out with this catalyst and the results were compared with bis(2,4,7-trimethylindenyl)zirconium dichloride (Cat-II) to investigate the steric effects of substituents on the catalytic activity and microstructure of the resulting polymer. The differences of the methyl group position in Cat-I and Cat-II have apparent effect on the polymerization behavior. Comparable activity of the catalyst was observed at 0 and 25 °C polymerization temperature and the microstructure of the polymer was almost the same.     

Characterizing polymorphism and crystal transformation of polylactide by terahertz time-domain spectroscopy

Terahertz time-domain spectroscopy (THz-TDS), which has been proved to show promising application in complex polymer systems, was employed to investigate the polymorphism phenomenon and crystal transformation of polylactide (PLA) in this study. The THz-TDS shows sensitive response on the crystal structure. The α'-form, α-form and stereocomplex crystals exhibit absorption peaks of lattice vibration at 1.82, 2.01 and 2.09 THz, respectively. THz-TDS has no direct chirality identification on the difference between poly (d-lactide) (PDLA) and poly(l-lactide) (PLLA). However, the PLA stereocomplex shows an extra and distinctive absorption peak at 1.43 THz compared with homo-PLA, and the peak was proved to be stemmed from the collective vibration of L-lactic unit and D-lactic unit pairs connecting by hydrogen bonds. This is the first time that THz-TDS has been proved to be of great potential in identification of polymer stereocomplex crystal. Also, the α'→α crystal transformation of PLA were intuitively investigated at 120 °C using THz-TDS, while the transformation rate was quite slow.