Preparation of silica‐supported late transition metal catalyst and ethylene polymerization

A Correction has been published for this article in Polymer International 51(6) 2002, 561 The late transition metal catalyst 2,6‐bis[1‐(2,6‐diisopropylphenylimino)ethyl]pyridine iron(II) chloride was supported on silica. Fourier transform infrared spectroscopy, scanning electronic micrograph and X‐ray photoelectron spectroscopy measurements were utilized to examine the process of supporting catalyst on silica and investigate the possible mechanism of support. Furthermore, ethylene polymerizations with the supported catalysts were carried out in various conditions such as different reaction temperatures and Al/Fe molar ratios. The results showed that MAO first reacted with the hydroxyl of silica forming Si? O? Al bonds and then the catalyst was bridged through MAO on the surface of silica. Compared with homogeneous catalysts, the supported catalysts show some decrease in catalyst activity. However, they can show good activity at a lower Al/Fe molar ratio with MAO as co‐catalyst and give rise to higher molecular weight and melting temperature of the polymer. Better morphology of polyethylene was obtained by a supported catalyst than by its corresponding homogeneous catalyst. The late transition metal catalyst 2,6‐bis[1‐(2,6‐diisopropylphenylimino)ethyl]pyridine iron(II) chloride was supported on silica. Fourier transform infrared spectroscopy, scanning electronic micrograph and X‐ray photoelectron spectroscopy measurements were utilized to examine the process of supporting catalyst on silica and investigate the possible mechanism of support. Furthermore, ethylene polymerizations with the supported catalysts were carried out in various conditions such as different reaction temperatures and Al/Fe molar ratios. The results showed that MAO first reacted with the hydroxyl of silica forming Si? O? Al bonds and then the catalyst was bridged through MAO on the surface of silica. Compared with homogeneous catalysts, the supported catalysts show some decrease in catalyst activity. However, they can show good activity at a lower Al/Fe molar ratio with MAO as co‐catalyst and give rise to higher molecular weight and melting temperature of the polymer. Better morphology of polyethylene was obtained by a supported catalyst than by its corresponding homogeneous catalyst. © 2002 Society of Chemical Industry     

Study of the compositional heterogeneity of ethylene/1–hexene copolymers produced over supported catalysts of different composition

Separation into narrow MWD fractions (liquid–liquid fractionation) and preparative TREF (temperature rising elution fractionation) with subsequent analysis of fractions by GPC, FTIR, and ¹³C NMR spectroscopy were used to study the comonomer distribution of ethylene/1–hexene copolymers produced over highly active supported titanium‐ and vanadium‐magnesium catalysts (TMC and VMC) and a supported zirconocene catalyst. These catalysts produce PE with different MWD: M_w/M_n values vary from 2.9 for zirconocene catalyst, 4.0 for TMC, and 15 for VMC. 1‐Hexene increases polydispersity to 25 for copolymer produced over VMC and hardly affects MWD of the copolymer produced over TMC and zirconocene catalysts. The most broad short chain branching distribution (SCBD) was found for ethylene/1–hexene copolymers produced over TMC. VMC and supported zirconocene catalyst produce copolymers with uniform profile of SCB content vs. molecular weight in spite of great differences in M_w/M_n values (22 and 2.5 respectively). TREF data showed that majority of copolymer produced over supported zirconocene catalyst was eluted at 70–90°C (about 85 wt %). In the case of VMC copolymer's fractions were eluted in the broad temperature interval (40–100°C). Accordingly, TREF data indicate a more homogeneous SCBD in copolymer, produced over supported zirconocene catalyst. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Ethylene polymerization over supported titanium‐magnesium catalysts: Effect of polymerization parameters on the molecular weight distribution of polyethylene

The data on the effects of polymerization duration, cocatalyst, and monomer concentrations upon ethylene polymerization in the absence of hydrogen, and the effect of an additional chain transfer agent (hydrogen) on the molecular weight (MW), molecular weight distribution (MWD), and content of vinyl terminal groups for polyethylene (PE) produced over the supported titanium‐magnesium catalyst (TMC) are obtained. The effects of these parameters on nonuniformity of active sites for different chain transfer reactions are analyzed by deconvolution of the experimental MWD curves into Flory components. It has been shown that the polymer MW grows, the MWD becomes narrower and the content of vinyl terminal groups in PE increases with increasing polymerization duration. It is assumed to occur due to the reduction of the rate of chain transfer with AlEt₃ with increasing polymerization duration. The polydispersity of PE is found to rise with increasing AlEt₃ concentration and decreasing monomer concentration due to the emergence of additional low molecular weight Flory components. The ratios of the individual rate constants of chain transfer with AlEt₃, monomer and hydrogen to the propagation rate constant have been calculated. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Copolymerization of ethylene and propylene catalyzed by novel magnesium chloride supported,vanadium‐based catalysts

Two novel magnesium chloride supported, vanadium‐based Ziegler–Natta catalysts with 9,9‐bis(methoxymethyl)fluorene and di‐i‐butyl phthalate as internal donors were prepared and used in the copolymerization of ethylene and propylene. The catalytic behaviors of these catalysts were investigated and compared with those of traditional magnesium chloride supported, vanadium‐based catalysts without internal donors. Differential scanning calorimetry, gel permeation chromatography, and ¹³C‐NMR spectroscopy analysis were performed to characterize the melting temperatures, molecular weights, and molecular weight distributions as well as structures and compositions of the products. The copolymerization kinetic results indicated that the novel catalyst with 9,9‐bis(methoxymethyl)fluorene as an internal donor had the highest catalytic activity and optimal kinetic behavior in ethylene–propylene copolymerization with an ethylene/propylene molar ratio of 44/56. Low‐crystallinity and high‐molecular‐weight copolymers were obtained with these novel magnesium chloride supported, vanadium‐based catalysts. The reactivity ratio data indicated that the catalytic systems had a tendency to produce random ethylene–propylene copolymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and evaluation of two new FI‐Ti catalysts for living polymerization of ethylene

Two new FI complexes, bis[N‐(3‐allylsalicylidene)‐pentafluoroanilinato]titanium(IV) dichloride ( AFI ) and bis[N‐(3‐propylsalicylidene)‐pentafluoroanilinato]titanium(IV) dichloride ( PFI ) were designed and synthesized as catalysts for living polymerization of ethylene. The two complexes were characterized by elemental analysis, spectroscopy and X‐ray single diffraction. The catalysts were evaluated in ethylene polymerization under atmospheric pressure. It was found that both catalysts exhibited high activity and good livingness. The effects of temperature and dMAO/Ti molar ratio on the polymerization behavior of AFI were studied in detail. Elevating temperature increased self‐immobilization of the AFI catalyst, which broadened the polymer molecular weight distribution. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Study of the morphology and kinetics of novel Ziegler–Natta catalysts for propylene polymerization

The morphological and kinetic characteristics of novel Ziegler–Natta catalysts were studied. Catalysts were prepared by Borealis Polymers Oy using a new synthesis technique (emulsion technology). Video microscopy was used to study the growth of single catalyst particles during polymerization in the gas and liquid phases. The distribution of single particle activity was very narrow in the catalyst without external support and was rather broad in the the silica‐supported catalyst. Video microscopy of molten polymer particles allowed observation of the process and degree of fragmentation of the catalyst particles. A correlation between the activation period during the initial stage of polymerization and catalyst fragmentation was found. Fragmentation was faster and more uniform with the catalyst without external support than with the silica‐supported catalyst. Scanning electron microscopy provided information on morphology evolution and shape replication of the catalyst particles. With the catalyst without external support, good shape replication was observed, and compact and spherical particles were formed. With the silica‐supported catalyst, shape replication was poor, and nonspherical porous polymer particle were formed. Modeling of the kinetics of propylene polymerization was done using a simple three‐step reaction scheme neglecting mass and heat transport effects. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2191–2200, 2005     

A New Heterogenization Technique for Single‐Site Polymerization Catalysts

Summary: Silica‐supported single‐site catalysts show limitations with respect to catalyst homogeneity and maximum metal content. A novel emulsion‐based catalyst heterogenization concept is described, which allows these limitations to be overcome. The method produces catalyst particles with an inherently perfect spherical shape and unique intra‐ and inter‐particle homogeneity. The catalyst particles are very compact and have a low surface area. Video microscopic studies confirm that the improved catalyst homogeneity leads to a more uniform polymerization behavior on a single particle level. The catalysts contain significantly more complex, compared to silica‐supported catalyst systems, which leads to correspondingly higher catalyst activities. No differences, in terms of the mass‐transfer kinetics of these low‐porosity catalysts, compared to porous catalyst systems have been observed.

Electron microscopy image of self‐supported single‐site catalyst prepared by the emulsion‐based method.     

Three‐site mechanism and molecular weight: Time dependency in liquid propylene batch polymerization using a MgCl2‐supported Ziegler‐Natta catalyst

This article demonstrates that the molecular weight of propylene homopolymer decreases with time, and that the molecular weight distribution (MWD) narrows when a highly active MgCl₂‐supported catalyst is used in a liquid pool polymerization at constant H₂ concentration and temperature. To track the change in molecular weight and its distribution during polymerization, small portions of homo polymer samples were taken during the reaction. These samples were analyzed by Cross Fractionation Chromatograph (CFC), and the resulting data were treated with a three‐site model. These analyses clearly showed that the high molecular weight fraction of the distribution decreases as a function of time. At the same time, the MWD narrows because the weight‐average molecular weight decreases faster than the number‐average molecular weight. A probable mechanism based on the reaction of an external donor with AlEt₃ is proposed to explain these phenomena. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1035–1047, 2001     

Preparation and characterization of core‐shell nanoparticles containing poly(chlorotrifluoroethylene‐co‐ethylvinylether) as core

Core shell latex particles with a glassy core and a low T_g polymeric shell are usually preferred. More so, the glassy core happens to be a fluoropolymer with a shell polymer that helps in processability. We describe here the preparation and characterization of core shell nanoparticles consisting of poly(chlorotrifluoroethylene‐co‐ethylvinylether) as core encapsulated in poly(styrene‐acrylate) copolymer shell using seeded emulsion polymerization method under kinetically controlled monomer starved conditions. Properties of the emulsion using surfactants (fluoro/conventional) and surfactant free conditions were investigated. Average size (100 nm), spherical shape and core–shell morphology of the latex particles was confirmed by dynamic light scattering and transmission electron microscopy. Absence of C? F and C? Cl peaks in X‐ray photoelectron spectroscopy proves that cores are completely covered. Polymerization in the presence of fluorocarbon surfactant was found to give optimum features like narrow size distribution, good shell deposition and no traces of agglomeration. Films of core shell latex particles exhibited improved transparency and enhanced water contact angles thus making them suitable for applications in various fields including coatings. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The effect of synthesis methods on the mechanical properties of self‐crosslinkable poly(n‐butyl methacrylate‐co‐N‐methylolacrylamide) films

The effects of particle size and parent polymer characteristics on the mechanical properties, gel fraction, and swelling index of self‐crosslinkable poly(n‐butyl methacrylate‐co‐N‐methylolacrylamide) films made by two‐stage emulsion or microemulsion polymerization in the presence of variable amounts of the chain transfer agent, n‐butyl mercaptan, are reported here. In films prepared with latexes made by microemulsion polymerization, the crosslinking degree increased greatly on curing; by contrast, in those made by emulsion polymerization, the crosslinking degree practically did not increase after curing. Stress–strain tests of uncured and cured films indicate that microemulsion‐made films are tougher than the emulsion‐made films. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and barrier property of poly(ethylene terephthalate)/clay nanocomposite using clay‐supported catalyst

Poly(ethylene terephthalate) (PET)/clay nanocomposite was prepared by the direct polymerization with clay‐supported catalyst. The reaction degree of catalyst against the cation exchange capacity of clay was 8 wt %. The intercalation of PET chains into the silicate layers was revealed by X‐ray diffraction studies. SEM morphology of the nanocomposite showed a good dispersion of clay‐supported catalyst, ranging from 30 to 100 nm. The intercalated and exfoliated clay‐supported catalyst in PET matrix was also observed by TEM. The improvement of O₂ permeability for PET/clay‐supported catalyst composite films over the pure PET is approximately factors of 11.3–15.6. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4875–4879, 2006     

Simplified preparation of low polydispersity,low molecular weight poly(D,L‐lactic acid) by liquid/liquid phase separation for drug delivery systems with discussion of molecular weight characterization

Poly(D ,L ‐lactic acid) (PLA) has been widely used in pharmaceutics and medicine. Low molecular weight (LMW) PLA is especially useful for rapidly degrading biomaterials such as those used for short‐duration drug delivery systems. There is scant information available in the literature regarding the purification and analysis of LMW PLA. In this paper we report (1) a convenient and effective polymer purification/fractionation technique to produce LMW PLA with narrow molecular weight distribution (MWD) and (2) analyses that were used to characterize the molecular weight and MWD of these polymers. A novel, convenient and effective temperature‐induced solution‐phase separation method was developed to produce narrow MWD, LMW (600–2000 g mol^?1) PLA. Molecular weights determined using gel permeation chromatography (GPC) with universal calibration, unlike those determined with the commonly used conventional calibration, showed good agreement with those obtained using several independent direct techniques. The phase separation induced by temperature reduction of a polymer in a single solvent system provided a simple and effective technique to produce narrow MWD, LMW PLA polymers. Additional advantages of this technique are: (1) only one solvent is required; (2) the risk of local complete solid polymer precipitation is eliminated; (3) it is reversible and not dependent on the rate of cooling; and (4) use of chlorinated solvents is avoided. This technology may open up a new opportunity for manufacturing LMW polymers with narrow MWD. We also found that GPC with universal calibration is a more accurate method than GPC with the commonly used conventional calibration for characterizing these polymers, and is straightforward to use especially now that on‐line viscosity detectors are widely available. Copyright © 2010 Society of Chemical Industry     

In Situ synthesis of inorganic filler‐filled polyethylene using polyethersulfone‐supported TiCl4 catalyst system

In situ ethylene polymerizations with inorganic fillers were performed using catalyst based on titanium tetrachloride supported on polyethersulfone. The inorganic fillers used were MgO, TiO₂, and CaCO₃, which were pretreated with cocatalyst (methylaluminoxine) for better dispersion onto the polymer matrix. The formation of polyethylene (PE) within the whole matrix was confirmed by Fourier transform infrared studies. The wide‐angle X‐ray diffraction profile of the synthesized PEs indicated the presence of crystalline region. It was found that the nature of inorganic filler did not have any remarkable effect on the melting characteristics of the polymer, but the degree of crystallinity of PE was found to be higher for TiO₂‐filled PE. The amount of filler incorporated into the matrix was also evaluated through thermogravimetric analysis, where TiO₂‐filled PE showed ～ 49% of filler material, which was also reflected in the higher productivity obtained by this system. The morphology of the filler‐filled PEs was different, whereas the elemental dispersion was found to be uniform on the surface as elucidated through energy‐dispersive X‐ray spectroscopy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Chemosynthesis and characterization of fully biomass‐based copolymers of ethylene glycol, 2,5‐furandicarboxylic acid,and succinic acid

Poly(ethylene 2,5‐furandicarboxylate‐co‐ethylene succinate) (PEFS) copolymers of 2,5‐furandicarboxylic acid (FDCA) and succinic acid with 11.98–91.32 mol % FDCA composition were synthesized via melt polycondensation in the presence of ethylene glycol using tetrabutyl titanate as a catalyst. PEFSs' molecular weight, thermal properties, and molar composition were determined by Fourier transform infrared spectroscopy, gel permeation chromatography, intrinsic viscosity, ¹H NMR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and wide‐angle X‐ray diffraction (WAXD) measurements. From experimental conditions, we obtained random copolymers with number‐average molecular weights exceeding 25,600, determined by GPC and ¹H NMR analyses. DSC analysis revealed that PEFS copolymers' melting temperatures differed depending on EF units' percentage. TGA studies confirmed that all PEFS copolymers' thermal stability exceeded 300°C. From WAXD analysis, it is observed that the PEFS copolymer crystal structure was similar to that of PES when EF unit was 11.98 mol % and to that of PEF when EF units were 74.35 and 91.32 mol %. These results benefit this novel biodegradable copolymer to be used as a potential biomaterial. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1415‐1420, 2013     

Modeling of the propylene polymerization catalyzed by single‐/multi‐active site catalyst: A Monte Carlo study

In the present study, a model is established to describe the propylene polymerization kinetics catalyzed by the typical catalysts with single‐/multi‐active site type in a liquid phase stirred‐tank reactor using the Monte Carlo simulation method, regardless of the mass and heat diffusion effects within the polymer particles. Many kinetic data, including polypropylene yield, concentration transformation of catalyst active sites, number–average molecular weight, etc., are obtained by the model. The simulated kinetic results are found to be in agreement with the reference ones obtained in a population balance model. Furthermore, the comparisons of the kinetic data between the polymerization catalyzed by the catalyst with single‐active site type (typically silica‐supported metallocene) and the catalyst with multi‐active site type (typically MgCl₂‐supported Ziegler‐Natta catalyst) have been studied using the model. Especially, the effects of hydrogen on the polymerization are studied using the model. The studied results show that the theory of catalyst active site can be used to explain the different propylene polymerization kinetics catalyzed by the typical catalyst with single‐/multi‐active site type. In addition, the role of hydrogen in the propylene polymerization needs to be emphasized. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation of ethylene/1‐octene copolymers from ethylene stock with tandem catalytic system

Tandem catalysis offers a novel synthetic route to the production of linear low‐density polyethylene. This article reports the use of homogeneous tandem catalytic systems for the synthesis of ethylene/1‐octene copolymers from ethylene stock as the sole monomer. The reported catalytic systems involving a highly selective, bis(diphenylphosphino)cyclohexylamine/Cr(acac)₃/methylaluminoxane (MAO) catalytic systems for the synthesis of 1‐hexene and 1‐octene, and a copolymerization metallocene catalyst, rac‐Et(Ind)₂ZrCl₂/MAO for the synthesis of ethylene/1‐octene copolymer. Analysis by means of DSC, GPC, and ¹³C‐NMR suggests that copolymers of 1‐hexene and ethylene and copolymers of 1‐octene and ethylene are produced with significant selectivity towards 1‐hexene and 1‐octene as comonomers incorporated into the polymer backbone respectively. We have demonstrated that, by the simple manipulation of the catalyst molar ratio and polymerization conditions, a series of branched polyethylenes with melting temperatures of 101.1–134.1°C and density of 0.922–0.950 g cm^?3 can be efficiently produced. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Well‐defined polymers containing 1,3‐dichloro‐tetra‐n‐butyl‐distannoxane moiety: Synthesis,mechanism, and applications in catalysis

A series of well‐defined different chain lengths polymers, which contain the organometallic 1,3‐dichloro‐tetra‐n‐butyl‐distannoxane core in the main chain, was obtained in one‐pot via a novel 1,3‐dichloro‐tetra‐n‐butyl‐distannoxane (complex A )/azobisisobutyronitrile (AIBN) initiating system used in reverse atom transfer radical polymerization of styrene in different concentrations. The introduction of organotin complex A was supported by ¹H‐NMR, ¹³C–NMR, and the Inductive Coupled Plasma Emission Spectrometer analysis of the organotin‐containing polymer. Moreover, the mechanism of polymerization was investigated by changing the ratio of complex A to AIBN. It was concluded that the complex A not only acted as an important part of the initiator system but also introduced the functional organometallic group into the polymer chain. Additionally, the organotin‐containing polymer could be used as catalyst for esterification, and the reaction products' conversion could reach high up to 99% and does not decrease after four successive cycles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

A new post‐metallocene catalyst for alkene polymerization: copolymerization of ethylene and 1‐hexene with titanium complexes bearing N,N‐dialkylcarbamato ligands

A new type of post‐metallocene polymerization catalyst based on titanium complexes with N,N‐dialkylcarbamato ligands was used to copolymerize ethylene and 1‐hexene. These easy‐to‐synthesize and stable complexes in combination with different organoaluminium co‐catalysts produce random ethylene/1‐hexene copolymers characterized by a broad molecular weight distribution and high 1‐hexene incorporation, as confirmed by SEC, DSC and ¹³C NMR analysis. The influence of the main reaction parameters on the polymerization reactions was studied including the type of catalyst components, solvent, temperature, the ethylene partial pressure and the [Al]/[Ti] ratio in the catalyst. A higher activity and a higher 1‐hexene incorporation were achieved with AlMe₃‐depleted methylalumoxane as co‐catalyst and chlorobenzene as solvent. © 2013 Society of Chemical Industry     

Synthesis and characterization of low relative molecular weight trans‐1,4‐poly(isoprene)

Low relative molecular weight trans‐1,4‐polyisoprene oligomers were synthesized successfully by bulk precipitation and solution polymerization with supported titanium catalyst using hydrogen as relative molecular weight modifier. The effects of polymerization conditions on intrinsic viscosity ([η]), catalyst efficiency (CE) and structure of polymer were studied. Increasing the hydrogen pressure resulted in the decrease of [η] of the polymer. With the increasing of hydrogen pressure and reaction temperature, CE decreased but still maintained above 2500 g polymer/g Ti. The percentage composition of (trans‐1, 4‐unit) in the polymer was over 90% in all results. The crystallinity of polymer was about 50–60% with T_m being about 60°C. The relative molecular weight distribution index (MWD) was quite difference according to the polymerization method. While number average molecular weight (M_n) exceeded 860, polymer turned from viscous materials to fragile wax materials, and then to toughness materials at 1800. Dynamic property testing showed that the additional of this oligomer could increase the wet‐skid resistance of the rubber. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Cationic polymerization of ethylene oxide with Maghnite‐H as a clay catalyst in the presence of ethylene glycol

The activated‐monomer cationic ring‐opening polymerization of ethylene oxide, initiated with ethylene glycol and using an acid‐exchanged montmorillonite clay called Maghnite‐H⁺ as an effective catalyst, was carried out to obtain the corresponding homopolymers with narrow polydispersity ratios. The molecular weights of the obtained polymers were controlled with the feed ratio of the monomer to the initiator. The effects of the amount of the catalyst and time on the polymerization yield and viscosity of the polymers were studied. The structure was confirmed with proton nuclear magnetic resonance and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009