Preparation and characterization of spherical PP/PB alloys with MgCl2-supported Ziegler-Natta catalyst

Polypropylene（PP）/polybutene-1（PB） alloys within reactor were prepared by MgCl₂-supported Ziegler-Natta catalyst with sequential two-stage polymerization technology.First,propylene homo-polymerizations were carried out to form isotactic polypropylene（iPP） particles containing active catalyst.Then,butene-1 was subsequently polymerized to form polybutene-1 phase inside the iPP particles.Finally,iPP/PB alloys with spherical shape and adjustable PB content were synthesized.The catalytic activity and catalytic stereospecificity of the Z-N catalyst in the two-stage polymerization process are discussed.The composition and physical properties of the PP alloys were characterized by FT-IR,¹³C-NMR,SEM,DSC and XRD.It was found that the in-reactor PP alloys are mainly composed of PP and PB with a little amount of poly（butene-co -propylene） random copolymers and poly（butene-block-propylene） block copolymers.SEM measurements verified that the PB phases with size in the range of 300-400 nm dispersed in the PP matrix uniformly.The incorporation of PB upon the PP matrix affects the properties of final products greatly.     

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.     

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...     

Production of octyl levulinate biolubricant over modified H-ZSM-5： Optimization by response surface methodology

The present study highlighted the use of modified H-ZSM-5 （Meso-HZ-5） as heterogeneous catalyst for the synthesis of octyl levulinate biolubricant by catalytic esterification of biomass derived renewable levulinic acid （LA） with n-octanol. The process variables such as catalyst loading （X1）, n-octanol to LA molar ratio （X2） and reaction temperature （X3） were optimized through response surface methodology （RSM）, using Box-Behnken model. Analysis of variance was performed to determine the adequacy and significance of the quadratic model. The yield of octyl levulinate was obtained to be 99% at optimum process parameters. The developed quadratic model was found to be adequate and statistically accurate with correlation value （R2） of 0.9971 to predict the yield of octyl levulinate biolubricant. The study was also extended on the validation of theoretical and experimental data, including catalyst reusability.     

Phase-transfer catalysis of a new cationic gemini surfactant with ester groups for nucleophilic substitution reaction

A highly effective phase transfer of a quaternary ammonium gemini surfactant with ester groups（（diethylhexanedioate） diyl-a,v-bis（dimethyl dodecyl ammonium bromide） referred to as 12-10-12）was synthesized with high yield and characterized by infrared spectroscopy, elemental analysis and1 HNMR. Then, 12-10-12 was used as a phase transfer catalyst to study the catalytic effect on the reaction of anhydrous sodium acetate and 4-methylbenzyl chloride. The possible catalytic mechanism and the influence of surfactant concentration, temperature and type are also discussed. The experimental results showed that the catalysis efficiency was more active than the traditional, single-chained surfactant,tetrabutyl ammonium bromide. It also revealed that the reaction was first-order with respect to the concentration of 4-methylbenzyl chloride. The concentration of 4-methylbenzyl chloride grew linearly with the concentration of 12-10-12 and as the reaction temperature increased. The optimum reaction time was 7 h.     

A convenient,highly-efficient method for preparation of hydroxyl-terminated isotactic poly(propylene) and functional di-block copolymer

Both terminated functional isotactic polypropylene （iPP） and block copolymers containing iPP segment are desirable for commercial applications. This paper provides a convenient, highly-efficient method to prepare hydroxyl-terminated isotactic polypropylene （iPP-t-OH） and functional di-block copolymer containing the iPP segment through a combination of coordination polymerization and coupling reaction. The coordination polymerization was catalyzed by TiCI4/MgCI2/AIEt3 catalyst system using ZnEt2 as chain transfer agent. Further, the Zn-terminated iPP was oxidized and subsequently hydrolyzed to provide iPP-t-OH. Soxhlet extraction and 13C NMR were used to calculate the isotacticity of iPP-t-OH. The degree of polymerization and the number of hydroxyl groups at the chain end of iPP-t-OH were measured by GPC and 1H NMR. Despite the high molecular weight and heterogeneous reaction, iPP-t-OH is effectively linked with PEG-t-NCO to produce di-block copolymers. DSC analysis of the di-block copolymer shows an obvious decrease in Tm and To, which indicated that PEG was successfully linked to the terminal end of iPP.     

Synthesis of polybutadienes with controllable microstructure by a novel binary Nd(3-NBSO3)3/alkylaluminum catalyst system

The polymerization of 1,3-butadiene was examined by using a novel halogen-free neodymium m-nitrobenzenesulfonate(Nd(3-NBSO3)3·donors)/alkylaluminum binary catalyst system. The catalyst showed fairly high activity and controllable selectivity. The microstructure of the resultant polymer was adjustable by variation of electron donor and/or the alkylaluminum. 13C-NMR and thermal analysis demonstrate that the produced polybutadienes have stereo-block chain structures of cis-1,4 and trans-1,4 segments with adjustable Tm and Tc. The neodymium sulfonate-based catalyst is believed to be significant in regulating the chain structure of polydienes and in exploring 1,3-diene polymerization mechanism.     

AROMATIC AND HETEROCYCLIC NITRILES AND THEIR POLYMERS ⅩⅧ. THE POLYMERIZATION KINETICS OF BENZONITRILE CATALYZED BY METAL ACETYLACETONATE

The bulk polymerization of benzonitrile catalyzed by Co(Ⅱ), Co(Ⅲ) and Fe(Ⅲ) acetylacetonate was studied. The results of kinetics study show that the rate of polymerization was proportional to first power of the concentration of catalyst and second power of the concentration of monomer.     

[Cu(TO)2(H2O)4](PA)2的制备、结构表征和热分解机理研究

[Cu（TO）2（H2O）4]（PA）2 was prepared by the reaction of aqueous 1,2,4-triazol-5-one （TO） solution with the solution of copper picrate Cu（PA）2 and characterized by elemental analysis, FT IR and X-ray powder diffraction analysis. The title complex has been studied by means of TG-DTG and DSC under conditions of linear temperature increase. The thermal decomposition residues were examined by FT IR analysis. Thermal decomposition mechanism of the title complex was proposed. In the temperature range of 30-680 ℃, the thermal decomposition process was composed of four major stages. The first stage was an endothermic process with the loss of four coordination water molecules. Since the dehydration product was unstable, when it was heated, it would be decomposed much more easily. The second stage was composed of an acute endothermic process and a continued strong exothermic process and the main decomposed residues were CuCO3, Cu（NCO）2 and polymers during this stage. The third stage was a sharp exothermic process, which resulted from the decomposition of the polymer. After the forth stage, the final decomposed residues were certainly copper oxide. The Arrhenius parameters have been also studied on the dehydration process and the first-step exothermic decomposition of [Cu（TO）2（H2O）4]（PA）2 using Kissinger＇s method and Ozawa-Doyle＇s method. The results using both methods were consistent with each other. The Arrhenius equation can be expressed as in k=24.0-179.8 × 10^3/RT for the dehydration process and in k= 16.7-206.0 × 10^3/RT for the first-step exothermic decomposition, on the basis of the average of Ea and In A through the two methods.     

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.     

Synthesis and characterization of trans-1,4-butadiene/isoprene copolymers: Determination of monomer reactivity ratios and temperature dependence

A series of trans-1,4-butadiene/isoprene copolymers were prepared using the catalyst system TiCl4/MgCl2-Al(iBu)3 with bulk precipitation technology at different temperatures. Monomers reactivity ratios were calculated based on the Kelen-Tüds(K-T) method and the Mao-Huglin(M-H) method. The influence of temperature on copolymer composition and polymerization rate was discussed in detail. The increase of reaction temperature brought the decrease of butadiene reactivity ratio rBd and supplied an effective adjustment on copolymers' composition distribution.     

Stereospecific polymerization of isobutyl vinyl ether by AIR3–VCl3·LiCl catalyst. II. Effects of polymerization conditions on polymerization

The effect of polymerization conditions such as aging time of the catalyst, polymerization temperature, polymerization time, monomer concentration, and catalyst concentration on the polymerization of isobutyl vinyl ether was intensively studied by using the VCI₃·LiCl–Al(i-Bu)₃ system at an Al(i-Bu)/VCl₃·LiCl ratio of 6 at which the cationic polymerization by VCl₃·LiCl is sufficiently depressed. About 10 min aging of the catalyst in the presence of monomer yields a fairly stable catalytie system. The optimum polymerization temperature is around 30°C. The conversion increased with increasing monomer concentration, whereas the stereospecificity of polymerization decreased. Unexpectedly, the conversion decreased as total catalyst concentration increased. This phenomenon is explained by considering the deactivation of catalytic sites by the excess of Al(i-Bu)₃. A reasonable mechanism from kinetic considerations is that two molecules of Al(i-Bu)₃ deactivate the catalytic site in an equilibrium reaction. This deactivation is understandable by considering that the coordination of two molecules of Al(i-Bu)₃ will occupy all the coordination positions of vanadium, so that there is no room for coordination of monomer coming to the catalytic site.     

Synthesis of polypropylene block copolymers from brominated styrene-terminated isotactic polypropylene

Isotactic polypropylene block copolymers, isotactic-polypropylene-block-poly (methyl methacrylate) (i-PP-b-PMMA) and isotactic-polypropylene-block-polystyrene (i-PP-b-PS), were prepared by atom transfer radical polymerization (ATRP) using a brominated styrene-terminated isotactic polypropylene macroinitiator synthesized from bromination of styrene-terminated isotactic polypropylene. The styrene-terminated isotactic polypropylene can be obtained by polymerization of propylene in the presence of styrene and hydrogen chain transfer agents using a rac-Me₂Si[2-methyl-4-(1-naphyl)Ind]₂ZrCl₂ as catalyst. The molecular weights of isotactic polypropylene block copolymers were controlled by altering the amount of hydrogen used in the polymerization of propylene and the amount of monomer used in the blocking reaction. The effect of i-PP-b-PS block copolymer on PP-PS blends and that of i-PP-b-PMMA block copolymer on PP-PMMA blends were studied by scanning electron microscopy.     

Monomer-isomerization polymerization. XXII.. Isomerization and polymerization of propenylbenzene with various ziegler–natta catalysts

The isomerization and polymerization of propenylbenzene (PB) with various Ziegler–Natta catalyst systems have been investigated. With the TiCl₃–(C₂H₅)₃Al (Al/Ti > 2.0) catalyst at 80°C, PB polymerized to give a polymer exclusively consisting of allylbenzene (AB) unit. During the polymerization, AB, which polymerized readily with the catalyst, was produced through isomerization of PB, indicating that PB underwent monomer-isomerization polymerization. PB also polymerized with isomerization to AB in the presence of TiCl₃?(C₂H₅)₂AlCl?NiCl₂ catalyst system, and a copolymer with PB and AB units was obtained. With TiCl₃?C₂H₅AlCl₂ catalyst, poly(PB) was formed via ordinary vinylene polymerization without isomerization. From these facts, it was concluded that the structure of the polymers produced from PB widely changed, depending on the catalyst systems used, which determine the rate of isomerization to AB and the polymerization reactivity of the PB and AB isomers formed.     

Synthesis of exfoliated isotactic polypropylene/functional alkyl-triphenylphosphonium-modified clay nanocomposites by in situ polymerization

Diphenyl (4-hydroxyphenyl) hexadecyl phosphonium bromide (POH) -modified montmorillonite (POHMMT) was used to prepare a novel TiCl₄/MgCl₂/POHMMT compound catalyst and exfoliated iPP/POHMMT nanocomposites were prepared by the in situ intercalative polymerization of propylene with the TiCl₄/MgCl₂/POHMMT compound catalyst. The POH surfactants don’t change the catalytic characteristic of the Z-N catalyst and the obtained PP presents high isotacticity, normal molecular weight and molecular weight distribution. The WAXD, SAXS and TEM results demonstrate the highly exfoliated iPP/POHMMT nanocomposites were produced by the in situ polymerization with this novel catalyst, while the intercalated iPP/Na⁺MMT nanocomposites were produced with the TiCl₄/MgCl₂/Na⁺MMT compound catalyst. Through this approach, in situ propylene polymerization can actually take place between the silicate layers and lead not only to PP with high isotacticity and molecular weight, but also to highly exfoliated PP nanocomposites.     

Polymerization of methyl methacrylate with ethylene bridged heterodinuclear metallocene of samarium and titanium

A novel heterodinuclear catalyst, ethylene bridged samarocene and titanocene chloride (Sm-Ti), was used both as a single component catalyst (cat.) and also by activation with triisobutyl aluminum (TIBA) to polymerize methyl methacrylate (MMA). The binary catalyst demonstrated higher activity than the single component, but the molecular weight of the resultant PMMA is lower. Ultrahigh molecular weight PMMA (1.5×10⁶) was obtained at an attractive conversion (87%) without any cocatalyst. The effects of polymerization parameters, such as temperature, time, molar ratios of Al(i-Bu)₃/cat. and MMA/cat., were studied in detail. The results showed that the catalytic activity had a rather different dependence on the polymerization temperature with/without TIBA. High molecular weight PMMA was much more easily prepared in a bulk system than in toluene solution. The polymer yielded with about 65% syndiotacticity by 1H NMR and 75% by IR spectroscopy, but its stereoregularity did not change too much with polymerization temperature and the concentration of TIBA.     

Homo and block copolymers of tert-butyl methacrylate by atom transfer radical polymerization

Atom transfer radical polymerization (ATRP) of tert-butyl methacrylate (tBMA) was investigated using cuprous bromide with different ligands, solvents, deactivators, etc. The polymerization in bulk and diphenyl ether solvent system performed using Cu(I)Br complexed with N, N, N′, N″, N″-pentamethyldiethylenetriamine (PMDETA) catalyst in conjunction with 2-bromopropionitrile as an initiator at room temperature showed a curvature in the first-order kinetic plot. The controlled polymerization in methanol solution resulted in slower rate of polymerization and lower molecular weights. Well-defined diblock copolymers of PSt-b-PtBMA synthesized by polystyrene bromo macroinitiator (PSt-Br) with Cu(I)Cl/PMDETA catalyst system yielded predetermined molecular weights and lower polydispersities. Otherwise, the Cu(I)Br/PMDETA catalytic system showed an inefficient polymerization of tert-butyl methacrylate with lower molecular weights and higher polydispersities. Subsequent hydrolysis of the homopolymer refluxed in dioxane with addition of HCl afforded well-defined poly(methacrylic acid).     

Acyclic diene metathesis polymerization of tailor-made monomers towards sequence-regulated vinyl copolymers

 Acyclic diene metathesis polymerization (ADMET) enables convenient transfer of sequential information of the designed monomers to the corresponding sequence-regulated copolymers. In this study, two structurally symmetric monomers, M1 and M2, were synthesized via atom transfer radical addition (ATRA) of diethyl meso-2,5-dibromohexanedioate with 1,5-hexadiene and 1,7-octadiene, respectively. Thus, sequenced segment of VB-EA-EA-VB (VB and EA represent vinyl bromide and ethyl acrylate, respectively) was incorporated into the ADMET diene monomers. ADMET polymerization of these two monomers with Grubbs first generation catalyst (Grubbs-I) was performed in CH₂Cl₂ at 40℃ for 5 days under nitrogen purge. Effects of catalyst amount, monomer concentration and methanol precipitation on the M_p and PDI of polymers were investigated by GPC, and the structures of the formed polymers were characterized by NMR. Our results indicate that using 3.0 mol% of Grubbs-I to monomer can afford polymers with high M_p. Moreover, selective precipitation in methanol enables complete removal of low molecular weight components from the crude products. Meanwhile, M2 exhibits higher ADMET polymerization reactivity than M1 due to its capability of suppressing negative neighboring group effect.     

1,2- and 3,4-rich polyisoprene synthesized by Mo(VI)-based catalyst with phosphorus ligand

Polyisoprene with relatively high content of 1,2/3,4 structure was synthesized using a novel catalyst system composed of MoO₂Cl₂ supported by phosphorus ligand and Al(OPhCH₃)(i-Bu)₂ as co-catalyst. The effects of phosphites, phosphates and phosphoric acid as ligands were investigated in the coordination polymerization of isoprene in the chosen catalyst system. The studied ligands significantly affected the catalytic activity of the Mo–Al catalytic active center without significant effect on the stereoselectivity. Mo(VI)-based catalyst system was proved to be highly effective in the polymerization of isoprene even at low [Al]/[Mo] ratio (10), affording polyisoprene with 1,2- and 3,4-% structural units in the range of 44.6–52.5%, high molecular weights M_n ~ 10⁵, and relatively broad molecular weight distributions (M_w/M_n = 3.0–4.4). The effect of molar ratio of phosphorous ligand to Mo-catalyst on catalyst activity of isoprene polymerization was discussed, and the structures of Mo–phosphite complexes were preliminarily studied by IR.