STUDY ON CATIONIC RING-OPENING COPOLYMERIZATION OF 1,4-ANHYDRO-2,3-DI-O-BENZYL-α-D-RIBOPYRANOSE WITH 1,4-ANHYDRO-2,3-O-ISOPROPYLIDENE-α-D-RIBOPYRANOSE

Cationic ring-opening copolymerization of 1, 4-anhydro-2, 3-O-isopropylidene-α-D-ribo-pyranose (AIRP) with 1,4-anhydro-2,3-di-O-benzyl-α-D-ribopyranose (ADBR) preparedfrom D-ribose was studied. Copolymerization using SbCl_5 or BF_3 OEt_2 as catalyst atlow temperature gave stereoregular (1→4)β-D-ribofuranan (C-1 and C-4 ring cleavagesee Scheme 1) or (1→5) α-D-ribofuranan (C-1 and C-5 ring cleavage) respectively. Theeffects of catalysts, reaction time and temperatures on yield and stereoregularity of the ob-tained polymers were studied. Polymers were characterized by molecular weight, ~1HNMR,~(13)CNMR and optical rotation.     

THE MOLECULAR WEIGHT AND ITS DISTRIBUTION OF 1, 2-POLYBUTADIENES PREPARED WITH MOLYBDENUM CATALYST SYSTEMS

The study on the molecular weight and its distribution of 1, 2-polybutadienes prepared with MoCl_4OR-i-Bu_2AlOR' catalyst systems has been carded out by viscosity and GPC methods. 1, 2-Polybutadienes with (?)=1.2-2.0can be obtained with these catalyst systems at 30—70℃. There is a linear relation between the (?) and the polymerization temperature. It was found by extrapolation that these catalyst systems may possibly initiate a living polymerization at the temperature near 18℃. The molecular weight of the polymers can be regulated either by polymerization temperature or by adding polar compounds such as allyl halides.     

POLYMERIZATION OF ETHYLENE WITH UNSYMMETRIC 2,6-BIS(IMINO)PYRIDINE IRON(Ⅱ)COMPLEX

An unsymmetric 2,6-bis(imino)pyridine iron(II) complex 1' was synthesized. The relationship between catalyststructure and its activity in ethylene polymerization is discussed. The kinetic behavior of ethylene polymerization and theeffects of polymerization conditions such as temperature, aluminum/iron molar ratio on the activity of catalyst and thecharacteristics of polyethylene were reported. The unsymmetric catalyst 1' has a good catalytic performance of 3.47×10~6 gPE·mol~(-1)·Fe·h~(-1) at 40℃ with aluminum/iron molar ratio = 2500. A dependence of catalyst activity on themethylaluminoxane (MAO) concentration and reaction temperature was found. The molecular weight (MW) of polyethylenewith broad dispersity is about 10~4-10~5 g/mol. The melting temperature and branching of polyethylenes vary with changingreaction temperature and aluminum/iron molar ratio.     

SYNTHESIS, CHARACTERIZATION AND NANOPARTICLE FORMATION OF STAR-SHAPED POLY(L-LACTIDE) WITH SIX ARMS

Well-defined star-shaped poly(L-lactide)with six arms(sPLLA)was synthesized via the ring-opening polymerization of L-lactide using dipentaerythritol as initiator and stannous octoate as catalyst in bulk at 125~C.The effects of molar ratios of both monomer to initiator and monomer to catalyst on the molecular weights of as-synthesized sPLLA polymers were in detail investigated.The molecular weights of sPLLA polymers linearly increased with the molar ratio of monomer to initiator,and the molecular weight d...     

Biodegradable thermogel as culture matrix of bone marrow mesenchymal stem cells for potential cartilage tissue engineering

Poly（lactide-co-glycolide）-poly（ethylene glycol）-poly（lactide-co-glycolide）（PLGA-PEG-PLGA） triblock copolymer was synthesized through the ring-opening polymerization of LA and GA with PEG as macroinitiator and stannous octoate as catalyst. The amphiphilic copolymer self-assembled into micelles in aqueous solutions, and formed hydrogels as the increase of temperature at relatively high concentrations（〉 15 wt%）. The favorable degradability of the hydrogel was confirmed by in vitro and in vivo degradation experiments. The good cellular and tissular compatibilities of the thermogel were demonstrated. The excellent adhesion and proliferation of bone marrow mesenchymal stem cells endowed PLGA-PEGPLGA thermogelling hydrogel with fascinating prospect for cartilage tissue engineering.     

MECHANISM-TRANSFORMATION SYNTHESIS AND CHARACTERIZATION OF POLY(STYRENE-b-2-ETHYL-2-OXAZOLINE) DIBLOCK COPOLYMER*

By mechanism-transformation (anionic→ cationic) poly(styrene- b-2-ethyl -2-oxazoline) diblockcopolymer, PS-b-PEOx, was synthesized in two steps. The first step is the polymerization of styrene blockcapped with ethylene oxide and its tosylation; the second step is the cationic ring-opening polymerization of2-ethyl-2-oxazoline. The products were thoroughly characterized by various methods, such as ~1H-NMR, IR,DMA, TEM and SAXS. The results show that the copolymer obtained possesses high molecular weight andnarrow molecular weight distribution.     

HIGHLY ACTIVE CATALYTIC STEREOSPECIFIC POLYMERIZATION OF STYRENE

A novel highly active catalyst of TiCl_4/MgCl_2--Al(C_2H_5), system (called SN-1 catalyst, in whichrare earth compound NdCl_3, is included) was used for studying stereospecific polymerization of styrenein benzene solution. Highly isotactic polystyrene was prepared with far better yield and higher cataly-tic efficiency than the results ever reported in literatures. The influences of concentration of mono-mer, catalyst, triethyaluminum as well as polymerization temperature on the catalytic efficiency, yield,tacticity and molecular weight of polystytene have been investigated.     

Polymerization Kinetics of Propylene with the MgCl_2-Supported Ziegler-Natta Catalysts——Active Centers with Different Tacticity and Fragmentation of the Catalyst

The catalytic activity and stereospecificity of olefin polymerization by using heterogeneous TiCl_4/MgCl_2 Ziegler-Natta(Z-N) catalysts are determined by the structure and nature of active centers, which are mysterious and fairly controversial. In this work, the propylene polymerization kinetics under different polymerization temperatures by using Z-N catalysts were investigated through monitoring the concentration of active centers [C*] with different tacticity. SEM was applied to characterize the catalyst morphologies and growing polypropylene(PP) particles. The lamellar thickness and crystallizability of PP obtained under different polymerization conditions were analyzed by DSC and SAXS. The PP fractions and active centers with different tacticity were obtained with solvent extraction fractionation method. The catalytic activity, active centers with different tacticity and propagation rate constant k_p, fragmentation of the catalyst, crystalline structure of PP are correlated with temperature and time for propylene polymerizations. The polymerization temperature and time show complex influences on the propylene polymerization. The higher polymerization temperature(60 ℃) resulted higher activity, k_p and lower [C*], and the isotactic active centers C_i* as the majority ones producing the highest isotactic polypropylene(iPP) components showed much higher k_p when compared with the active centers with lower stereoselectivity. Appropriate polymerization time provided full fragmentation of the catalyst and minimum diffusion limitation. This work aims to elucidate the formation and evolution of active centers with different tacticity under different polymerization temperature and time and its relations with the fragmentation of the PP/catalyst particles, and provide the solutions to the improvement of catalyst activity and isotacticity of PP.     

HIGH ACTIVITY AND GOOD HYDROGEN RESPONSE SILICA-SUPPORTED ZIEGLER-NATTA CATALYST FOR ETHYLENE POLYMERIZATION

正A silica-supported Ziegler-Natta catalyst with dimethyldichlorosilane(DMDS)as modifier and small silica as support was successfully prepared and characterized.Results from pilot screen showed that the new catalyst exhibited higher catalytic activity,better hydrogen response ability and better copolymerization ability than the commercial M catalyst.Pilot screen in ethylene gas phase fluidized bed polymerization,the catalytic activity of the new catalyst was up to 8000 g PE/g cat,which was twice of that of the commercial M catalyst.The bulk density of polyethylene obtained with the new catalyst was 0.38 g/cm~3.The new catalyst is suitable for condensed and super-condensed process in fluidized bed ethylene polymerization.     

THERMOSENSITIVITY OF NARROW-DISPERSED POLY(N-n-PROPYLACRYLAMIDE) PREPARED BY ATOM TRANSFER RADICAL POLYMERIZATION

Controlled polymerization of N-n-propylacrylamide was achieved by atom transfer radical polymerization(ATRP) in a N,N-dimethylformamide-water mixture(50 vol%)at room temperature with methyl 2-chloropropinonate as initiator and CuCl/tris(2-dimethylaminoethyl)amine as the catalytic system in a ratio of 1:1:1.High molecular weight homopolymers(up to 3.7×10~4)with narrow molecular weight distribution(less than 1.2)were obtained.The living character of the polymerization was further demonstrated by self-block...     

新型取代硅桥联茂稀土化合物的合成及在纳米级氢化钠助催化剂作用下高活性催化甲基丙烯酸甲酯聚合的研究

The synthesis and characterization of four new silicon-linked lanthanocene complexes with pendant phenyl groups on cyclopentadiene were reported. Based on the data of elemental analyses, MS and IR, the complexes were presumed to be unsolvated and dimeric complexes [Me2Si(C5H3CMe2C6H5)2LnC1]2 [Ln=Er (1), Gd (2), Sm (3), Dy (4)]. In conjunction with AlEt3 or sodium hydride as the co-catalyst, these complexes could efficiently catalyze the polymerization of methyl methacrylate (MMA). When the nanometric sodium hydride was used as a co-catalyst, the complexes were highly effective for the polymerization of MMA. At low temperature and in short time, in [MeESi(C5H3CMe2C6H5)2LnC1]2/NaH (nanometric) system, the polymer was obtained in more than 80% yield and the molecular weight was greater than 105. The activity reached that of organolanthanide hydride as a single-component catalyst. In ]MeESi(C5H3CMe2C6H5)2ErC1]2/Nail (nanometric) system, the effects of the molar ratio of MMA/catalyst and catalyst/co-catalyst, and the temperature on polymerization were studied.     

A metal-free coordination–insertion ring-opening polymerization of tetrahydrofuran by the central metalloid bis(pentafluorophenyl)(phenoxy)borane

A new strategy for the metal-free coordination–insertion ring-opening polymerization of tetrahydrofuran by the central metalloid Boron has been first identified. Bis(pentafluorophenyl)(phenoxy)borane was used as a catalyst for the polymerization reaction system. And polytetrahydrofuran with high molecular weight and narrow molecular weight distribution could be obtained. The proposed mechanism was studied by MALDI-TOF, ESI-MS and O-18 isotope labeling analyses as a metal-free coordination insert...     

Studies on the Self-condensing Vinyl Polymerization of a Novel Maleimide Inimer

The self-condensing vinyl polymerization(SCVP) of a novel maleimide inimer(initiator-monomer) 1, N-(4-α-bromobutyryloxy phenyl) maleimide with the complex of CuBr/Bipy (2, 2‘-bipyridine) as the catalyst was studied. GPC was used to determine the molecular weight and the results show that the molecular weight increases exponentially with polymerization time during the first hour, and then the rate of increase molecular weight slows down. The molecular weight also increases with increasing dosage of the catalyst. The coincidence of the molecular weights determined by ^1H NMR and GPC proves that the polymer obtained from the SCVP of inimer 1 has a linear structure, whichis further verified by ^13C NMR spectrum. A hyperbranched polymer was obtained by the copolymerization of inimer 1 and styrene.     

Polymerization of lactic <Emphasis Type="Italic">O</Emphasis>-carboxylic anhydride using organometallic catalysts

The ring-opening polymerization of 5-methyl-1,3-dioxolane-2,4-dione(lactic O-carboxylic anhydride,LacOCA) using organometallic complexes,including Co(Ⅲ) complexes with Schiff base ligands,Tin(Ⅱ) alphatates and Al(Ⅲ) complexes with Schiff base ligands,was explored.The polymerization was carried out by treatment of the organometallic complexes with LacOCA in toluene under mild conditions.The corresponding poly(lactic acid) was characterized by spectroscopy and thermal analyses,which revealed insight into the structure of the effective catalyst for the polymerization of LacOCA.     

"CAGE" VANADYL POLYCARBOXYLATE-THIOUREA COMPLEX FOR THE POLYMERIZATION OF ACRYLONITRILE

The polymerization of acrylonitrile (AN) in aqueous nitric acid initiated by " cage " vanadyl polycarboxylate (P=VO)-thiourea (TU) complex was investigated. The overall rate ofpolymerization isThe relationship between the induction period (τ) and the temperature of polymerization as well as the concentrations of reactants can be expressed as follows :The molecular weight of polyacrylonitrile increases with increasing monomer concentration and decreases with increasing temperature of polymerization and concentrations of vanadyl polycarboxylate and thioureaThe polymerization mechanism was proposed and discussed.     

POLYMERIZATION OF γ-STEARYL-α,l-GLUTAMATE N-CARBOXYANHYDRIDE USING RARE EARTH COORDINATION CATALYSTS*

A rare earth coordination system was first investigated as a new type of catalyst for the ring-openingpolymerization of α-amino acid N-carboxyanhydrides (NCAs). The results for the polymerization of γ-stearyl-α,L-glutamate(SLG) NCA using neodymium acetylacetonate (Nd(acac)_3)- or neodymium tris(2-ethylhexylphosphonate) (Nd(P_(204))_3)-triethylaluminum-water as catalysts were compared with those using conventional catalysts. It was found that the helicalpoly(γ-stearyl-L-glutamate) with high molecular weight as well as narrow molecular weight distribution can be obtained inthe presence of Nd(acac)_3/AlEt_3-1/2H_2O. The polymer obtained was characterized by IR and NMR spectroscopy.     

Highly chemoselective lipase from Candida sp.99-125 catalyzed ring-opening polymerization for direct synthesis of thiol-terminated poly(e-caprolactone)

Lipase from Candida sp.99-125 catalyzed ring-opening polymerization of e-caprolactone in the presence of 6-mercapto-1-hexanol was presented as a new metal-free approach for direct synthesis of welldefined thiol-terminated poly(e-caprolactone).Remarkably,high chemoselectivity of lipase from Candida sp.99-125 toward hydroxyl and thiol was exhibited and quantitative thiol fidelity over 90% was achieved.The tedious protecting/deprotecting steps for thiol and metal residue were avoided.The polymerizations with around 70% monomer conversion were conducted in bulk and toluene at relative low temperature of 40 8C.Number–average molecular weight of resulted polymers ranged from 3000 to4700 Da by changing the feed ratio between monomer and initiator.The structures of obtained thiolterminated poly(e-caprolactone) were demonstrated by combining NMR and SEC analyses.     

SYNTHESIS OF BRANCHED POLYETHYLENE USING (α-DIIMINE)NICKEL(Ⅱ)TiCl4 COMBINED AND SUPPORTED CATALYST*

(α-Diimine)nickel(Ⅱ) {[C6H5 -N = C(CH3)-C(CH3) = N -C6H5]NiBr2}-TiCl4 abbreviated as NiL-TiCl4 combined catalyst which is supported on MgCl2-SiO2 carrier has been prepared, by using alkyl aluminum (AIR3) as the cocatalyst in place of methylaluminoxane (MAO) to catalyze ethylene oligomerization and copolymerization in situ. The influences of procedure for supporting NiL-TiCI4, the molar ratio of NiL to TiCI4, cocatalyst type and polymerization temperature on the catalytic performance were studied. The degree of branching and the composition of the branched chain of polymers produced have been investigated by IR and ^13C-NMR spectra. The results show that the combined catalyst can synthesize the branched polyethylene with various banched chains .The polymerization reaction was monitored by gas chromatography and mass spectrometry (GC-MS). The results show that this catalyst promotes the oligomerization and copolymerization in situ for ethylene.     

CH_4 REFORMING WITH CO_2 TO SYNTHESIS GAS

An Ni-RE_2O_3/Al_2O_3 catalyst was used for CH_4 reforming with CO_2.Theinfluence of reaction conditions,such as temperature,space velocity,pressure,CO_2/CH_4 and H_2O/(CO_2+CH_4)ratios on the activity of catalyst was investigated.The re-sults show that CO/H_2 ratio was adjustable and the maximum content of CO reached50% in products which conformed with the composition of thermodynamical equilib-rium.In addition,the effect of carbon deposition on the catalyst upon the activitywas discussed.     

Ligand Steric Effects on Naphthyl-α-diimine Nickel Catalyzed α-Olefin Polymerization

Naphthyl-α-diimine nickel complexes with systematically varied ligand sterics, activated by modified methylaluminoxane(MMAO), were tested in the polymerization of higher α-olefin(1-hexene, 1-decene and 1-hexadecene) under suitable conditions. The polymerization results indicated the possibility of precise microstructure control, depending on catalyst structure, polymerization temperature, monomer concentration and types of monomers, which in turn strongly affects the resultant polymer properties. Naphthyl-α-diimine nickel complex bearing chiral bulky sec-phenethyl groups in the o-naphthyl position showed good catalytic activity, and resulted in branched polymers(42-88/1000 C) with high molecular weights(M_n:(4.3-15.2) × 10~4 g·mol~(-1)) and narrow molecular weight distribution(M_w/M_n = 1.13-1.29, RT), which suggested a living polymerization. The increasing steric hindrance of catalyst leads to enhance insertion for 2,1-insertion of α-olefin and the chain-walking reaction.