Block copolymer micelles as nanoreactors for single‐site polymerization catalysts

New micelle‐like organic supports for single site catalysts based on the self‐assembly of polystyrene‐b‐poly(4‐vinylbenzoic acid) block copolymers have been designed. These block copolymers were synthesized by sequential atom transfer radical polymerization (ATRP) of styrene and methyl 4‐vinylbenzoate, followed by hydrolysis. As evidenced by dynamic light scattering, self‐assembly in toluene that is a selective solvent of polystyrene, induced the formation of micelle‐like nanoparticles composed of a poly(4‐vinylbenzoic acid) core and a polystyrene corona. Further addition of trimethylaluminium (TMA) afforded in situ MAO‐like species by diffusion of TMA into the core of the micelles and its subsequent reaction with the benzoic acid groups. Such reactive micelles then served as nanoreactors, MAO‐like species being efficient activators of 2,6‐bis[1‐{(2,6‐diisopropylphenyl)imino}ethyl]pyridinyl iron toward ethylene polymerization. These new micelle‐like organic supports enabled the production of polyethylene beads with a spherical morphology and a high bulk density through homogeneous‐like catalysis. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 197–209, 2009     

Functionalized Star‐Like Polystyrenes as Organic Supports of a Tridentate Bis(imino)pyridinyliron/Aluminic Derivative Catalytic System for Ethylene Polymerization

Summary: Star‐like polystyrenes composed of a microgel core with arms functionalized with a few hydroxy‐ or methoxy‐ended ethylene oxide units were used as organic supports for a tridentate bis(imino)pyridinyliron catalyst towards ethylene polymerization. When used as supports of 2,6‐bis[1‐2,6(diisopropylphenyl)imino]ethylpyridynyl iron dichloride in the presence of various alkylaluminium compounds, the supported catalysts enabled the production, with a high catalytic activity, of polyethylene beads of a spherical morphology and high bulk density. A good control of the polyethylene molar mass distribution could also be achieved, which was explained by a lowering of the transfer reaction to the aluminium derivative, as compared to homogeneous conditions.

SEM image of PE particles prepared in the presence of trimethylaluminium supported on a PS microgel with an iron catalyst (TMA/Fe = 800).     

Cu(0)/2,6‐bis(imino)pyridines catalyzed single‐electron transfer‐living radical polymerization of methyl methacrylate initiated with poly(vinylidene fluoride‐co‐chlorotrifluoroethylene)

A series of 2,6‐bis(imino)pyridines, as common ligands for late transition metal catalyst in ethylene coordination polymerization, were successfully employed in single‐electron transfer‐living radical polymerization (SET‐LRP) of methyl methacrylate (MMA) by using poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) (P(VDF‐co‐CTFE)) as macroinitiator with low concentration of copper catalyst under relative mild‐reaction conditions. Well‐controlled polymerization features were observed under varied reaction conditions including reaction temperature, catalyst concentration, as well as monomer amount in feed. The typical side reactions including the chain‐transfer reaction and dehydrochlorination reaction happened on P(VDF‐co‐CTFE) in atom‐transfer radical polymerization process were avoided in current system. The relationship between the catalytic activity and the chemical structure of 2,6‐bis(imino)pyridine ligands was investigated by comparing both the electrochemical properties of Cu(II)/2,6‐bis(imino)pyridine and the kinetic results of SET‐LRP of MMA catalyzed with different ligands. The substitute groups onto N‐binding sites with proper steric bulk and electron donating are desirable for both high‐propagation reaction rate and C? Cl bonds activation capability on P(VDF‐co‐CTFE). The catalytic activity of Cu(0)/2,6‐bis(imino)pyridines is comparable with Cu(0)/2,2′‐bipyridine under the consistent reaction conditions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4378–4388     

Effects of hydrogen in ethylene polymerization and oligomerization with magnesium chloride‐supported bis(imino)pyridyl iron catalysts

The effects of hydrogen in ethylene polymerization and oligomerization with different bis(imino)pyridyl iron(II) complexes immobilized on supports of type MgCl₂/AlEt_n(OEt)_3–n have been investigated. Hydrogen has a significant activating effect on polymerization catalysts containing relatively bulky bis(imino)pyridyl ligands, but this is not the case in ethylene oligomerization with a catalyst containing relatively little steric bulk in the ligand. It was found that the presence of hydrogen in the latter system led to decreased activity and an overall increase rather than a decrease in product molecular weight, indicating deactivation of active species producing low molecular weight polymer and oligomer. Decreased formation of vinyl‐terminated oligomers in the presence of hydrogen can therefore contribute to the activating effect of hydrogen in ethylene polymerization with immobilized iron catalysts, if it is assumed that hydrogen activation is related to chain transfer after a 2,1‐insertion of a vinyl‐terminated oligomer into the growing polymer chain. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4054–4061, 2007     

Ethylene polymerization by novel Ziegler–Natta‐type catalysts obtained in situ by the oxidative addition of 8‐hydroxyquinoline‐based ligands to bis(1,5‐cyclooctadiene)nickel(0) and methylaluminoxane

Novel catalytic systems, prepared in situ by the oxidative addition of 8‐hydroxyquinoline ligands to bis(1,5‐cyclooctadiene)nickel(0) and activated by methylaluminoxane, were studied in ethylene polymerization. When 8‐hydroxyquinoline was employed, only oligomeric products were obtained. On the contrary, 5,7‐dinitro‐8‐hydroxyquinoline gave linear polyethylene (PE), but with a modest activity. For the catalyst based on 5‐nitro‐8‐hydroxyquinoline, the productivity was largely dependent on the content of free trimethylaluminum (TMA) present in the commercial aluminoxane. The progressive optimization of the TMA/oligomeric methylaluminoxane ratio increased the productivity, which reached 700 kg of PE/(mol of Ni × h), by an order of magnitude. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 200–206, 2006     

Mitigating chain‐transfer and enhancing the thermal stability of co‐based olefin polymerization catalysts through sterically demanding ligands

Sterically demanding Fe‐ and Co‐based olefin polymerization catalysts 2‐Fe and 2‐Co bearing 2,6‐bis(biphenylmethyl)‐4‐methylaniline substituted bis(imino)pyridine ligands were synthesized and evaluated for ethylene polymerization. The late‐transition metal complexes were characterized by X‐ray diffraction, NMR spectroscopy, and HRMS, while their resultant polymers were characterized by size‐exclusion chromatography and ¹H NMR spectroscopy. While catalyst 2‐Fe was inactive, catalyst 2‐Co was found to polymerize ethylene and avoid any detectable chain‐transfer to aluminum events that are known to plague other Fe‐ and Co‐based catalyst systems and to limit molecular weight. Furthermore, 2‐Co displays virtually perfect thermal stability up to 80 °C and shows greatly enhanced thermal stability at 90 °C as compared to previously reported analogues. These observations are attributed to the extreme steric demand imposed by the ligand which mitigates catalyst transfer, deactivation, and decomposition reactions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3990–3995     

Preparation of macroporous functionalized polymer beads by a multistep polymerization and their application in zirconocene catalysts for ethylene polymerization

Macroporous functionalized polymer beads of poly(4‐vinylpyridine‐co‐1,4‐divinylbenzene) [P(VPy‐co‐DVB)] were prepared by a multistep polymerization, including a polystyrene (PS) shape template by emulsifier‐free emulsion polymerization, linear PS seeds by staged template suspension polymerization, and macroporous functionalized polymer beads of P(VPy‐co‐DVB) by multistep seeded polymerization. The polymer beads, having a cellular texture, were made of many small, spherical particles. The bead size was 10–50 μm, and the pore size was 0.1–1.5 μm. The polymer beads were used as supports for zirconocene catalysts in ethylene polymerization. They were very different from traditional polymer supports. The polymer beads could be exfoliated to yield many spherical particles dispersed in the resulting polyethylene particles during ethylene polymerization. The influence of the polymer beads on the catalytic behavior of the supported catalyst and morphology of the resulting polyethylene was investigated. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 873–880, 2003     

Synthesis of well‐defined macromonomers by the combination of atom transfer radical polymerization and a click reaction

This article presents a new strategy for synthesizing a series of well‐defined macromonomers. Bromine‐terminated polystyrene and poly(t‐butyl acrylate) with predetermined molecular weights and narrow distributions were prepared through the atom transfer radical polymerization of styrene and t‐butyl acrylate initiated with ethyl 2‐bromoisobutyrate. Then, azido‐terminated polymers were obtained through the bromine substitution reaction with sodium azide. Catalyzed by CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine, the azido end group reacted with propargyl methacrylate via a 1,3‐dipolar cycloaddition reaction, and ω‐methacryloyl‐functionalized macromonomers were thus obtained. The end‐group transformation yields were rather high, as characterized by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectra and ¹H NMR analysis. By this effective and facile approach, some novel macromonomers that otherwise are difficult to achieve, such as poly(ethylene oxide)‐block‐polystyrene, were easily prepared. Radical homopolymerizations of these macromonomers were performed, and a series of comb polymers were prepared. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6103–6113, 2006     

Long‐lived layered silicates‐immobilized 2,6‐bis(imino)pyridyl iron (II) catalysts for hybrid polyethylene nanocomposites by in situ polymerization: Effect of aryl ligand and silicate modification

Heterogeneous‐layered silicate‐immobilized 2,6‐bis(imino)pyridyl iron (II) dichloride/MMAO catalysts, in which the active polymerization species are intercalated within sodium‐ and organomodified‐layered silicate galleries, were prepared for producing hybrid exfoliated polyethylene (PE) nanocomposites by means of in situ polymerization. The inorganic filler was first treated with modified‐methylaluminoxane (MMAO) to produce a supported cocatalyst: MMAO reacts with silicates replacing most of the organic surfactant, thus modifying the original crystallographic clay order. MMAO anchored to the nanoclay was able to activate polymerization iron complexes initiating the polymer growth directly from the filler lamellae interlayer. The polymerization mechanism taking place in between the montmorillonite lamellae separates the layers, thus promoting deagglomeration and effective clay dispersion. Transmission electron microscopy revealed that in situ polymerization by catalytically active iron complexes intercalated within the lower organomodified clay led to fine dispersion and high exfoliation extent. The intercalated clay catalysts displayed a longer polymerization life‐time and brought about ethylene polymerization more efficiently than analogous homogeneous systems. PEs having higher molecular masses were obtained. These benefits resulted to be dependent more on the filler nature than on the ligand environment around the iron metal center and the experimental synthetic route. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 548–564, 2009     

Synthesis of mikto‐topology star polymer containing one cyclic arm

Well‐defined mikto‐topology star polystyrene composed of one cyclic arm and four linear arms was synthesized by a combination of atom transfer radical polymerization (ATRP) and Cu‐catalyzed azide‐alkyne cycloaddition (CuAAC) click reaction. First, the bromine‐alkyne α,ω‐linear polystyrenes containing four hydroxyl groups protected with acetone‐based ketal groups were synthesized by ATRP of styrene using a designed initiator. Then, the bromine end‐group was converted to the azide and the linear polystyrene was cyclized intra‐molecularly by the CuAAC reaction. The four hydroxyl groups were released by deprotection and then esterified with 2‐bromoisobutyryl bromide to produce a cyclic polymer bearing four ATRP initiating units. By subsequent ATRP of styrene to grow linear polymers with the cyclic polystyrene as a macroinitiator, the mikto‐topology star polymers were prepared. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Multi‐center nature of ethylene polymerization catalysts based on 2,6‐bis(imino)pyridyl complexes of iron and cobalt

2,6‐Bis(imino)pyridyl complexes of Fe and Co in combination with methylalumoxane form very active homogeneous catalytic systems for polymerization of ethylene. GPC analysis of the polymers prepared with the complexes indicates that the Co complexes produce single‐center catalysts whereas the Fe complexes produce catalysts with numerous types of active centers. Different centers in the latter catalyst systems respond differently to reaction conditions such as the reaction duration, the [MAO]:[Fe] ratio, the ethylene concentration, etc. The article examines the effects of reaction variables on the performance of both types of catalysts and proposes an explanation for the complex behavior of the catalysts derived from the Fe complexes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6159–6170, 2006     

Synthesis of new amphiphilic diblock copolymers containing poly(ethylene oxide) and poly(α‐olefin)

This article discusses an effective route to prepare amphiphilic diblock copolymers containing a poly(ethylene oxide) block and a polyolefin block that includes semicrystalline thermoplastics, such as polyethylene and syndiotactic polystyrene (s‐PS), and elastomers, such as poly(ethylene‐co‐1‐octene) and poly(ethylene‐co‐styrene) random copolymers. The broad choice of polyolefin blocks provides the amphiphilic copolymers with a wide range of thermal properties from high melting temperature ～270 °C to low glass‐transition temperature ～?60 °C. The chemistry involves two reaction steps, including the preparation of a borane group‐terminated polyolefin by the combination of a metallocene catalyst and a borane chain‐transfer agent as well as the interconversion of a borane terminal group to an anionic (? O^?K⁺) terminal group for the subsequent ring‐opening polymerization of ethylene oxide. The overall reaction process resembles a transformation from the metallocene polymerization of α‐olefins to the ring‐opening polymerization of ethylene oxide. The well‐defined reaction mechanisms in both steps provide the diblock copolymer with controlled molecular structure in terms of composition, molecular weight, moderate molecular weight distribution (M_w/M_n < 2.5), and absence of homopolymer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3416–3425, 2002     

Unique catalytic behavior of chromium complexes having halogenated bis(imino)pyridine ligands for ethylene polymerization

Reactions of CrCl₃(thf)₃ with bis(imino)pyridines gave a series of {bis(imino)pyridine}chromium(III) trichloride complexes, {2,6‐(RN?CMe)₂C₅H₃N}CrCl₃ [R = C₆HPr₂‐2,6 ( 1 ), C₆H₃Et₂‐2,6 ( 2 ), C₆H₃Me₂‐2,6 ( 3 ), C₆H₂Me₃‐2,4,6 ( 4 ), C₆H₃Me₂‐3,5 ( 5 ), C₆H₅ ( 6 ), cyclohexyl ( 7 ), 2‐methyl‐1‐naphthyl ( 8 ), C₆H₃F₂‐2,6 ( 9 ), C₆H₃Br₂‐2,6 ( 10 ), C₆F₅ ( 11 )]. Pseudo‐octahedral geometries of 6 , 10 , and 11 were revealed by X‐ray crystallography. The complexes having bulky substituents such as 1 – 4 showed high activity for ethylene polymerization in combination with modified methylaluminoxane (MMAO) to give linear polyethylenes. In sharp contrast, the pentafluorophenyl complex 11 /modified methylaluminoxane system was found to be moderately active for ethylene homopolymerization to give moderately branched polyethylene with only ethyl branches. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3368–3375, 2005     

Preparation of polyethylene block copolymers by a combination of postmetallocene catalysis of ethylene polymerization and atom transfer radical polymerization

The synthesis of block copolymers consisting of a polyethylene segment and either a poly(meth)acrylate or polystyrene segment was accomplished through the combination of postmetallocene-mediated ethylene polymerization and subsequent atom transfer radical polymerization. A vinyl-terminated polyethylene (number-average molecular weight = 1800, weight-average molecular weight/number-average molecular weight =1.70) was synthesized by the polymerization of ethylene with a phenoxyimine zirconium complex as a catalyst activated with methylalumoxane (MAO). This polyethylene was efficiently converted into an atom transfer radical polymerization macroinitiator by the addition of α-bromoisobutyric acid to the vinyl chain end, and the polyethylene macroinitiator was used for the atom transfer radical polymerization of n-butyl acrylate, methyl methacrylate, or styrene; this resulted in defined polyethylene-b-poly(n-butyl acrylate), polyethylene-b-poly(methyl methacrylate), and polyethylene-b-polystyrene block copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 496–504, 2004     

Prospects and crucial problems in oligomerization and polymerization with iron and cobalt complex catalysts

<正>The discovery of highly active 2,6-bis(imino)pyridyl iron and cobalt complexes provided a milestone of latetransition metal catalysts for ethylene oligomerization and polymerization with being currently investigated for the scale-up process.The crucial problems are remaining in the catalytic systems:the catalytic systems targeting ethylene polymerization produce more oligomers at elevated reaction temperatures,however,there is a recognizable amount of high-molecular-weight polyethylene remained in the modified catalytic system for the oligomerization process.Beyond the modification of bis(imino)pyridyl metal complexes,several alternative procatalysts' models have been developed in our group.This review highlighted the achievements in exploring new iron and cobalt complexes with tridentate NNN ligands as procatalysts for ethylene oligomerization and polymerization.     

Synthesis of H‐shaped complex macromolecular structures by combination of atom transfer radical polymerization,photoinduced radical coupling,ring‐opening polymerization,and iniferter processes

Three controlled/living polymerization processes, namely atom transfer radical polymerization (ATRP), ring‐opening polymerization (ROP) and iniferter polymerization, and photoinduced radical coupling reaction were combined for the preparation of ABCBD‐type H‐shaped complex copolymer. First, α‐benzophenone functional polystyrene (BP‐PS) and poly(methyl methacrylate) (BP‐PMMA) were prepared independently by ATRP. The resulting polymers were irradiated to form ketyl radicals by hydrogen abstraction of the excited benzophenone moieties present at each chain end. Coupling of these radicals resulted in the formation of polystyrene‐b‐poly(methyl methacrylate) (PS‐b‐PMMA) with benzpinacole structure at the junction point possessing both hydroxyl and iniferter functionalities. ROP of ε‐caprolactone (CL) by using PS‐b‐PMMA as bifunctional initiator, in the presence of stannous octoate yielded the corresponding tetrablock copolymer, PCL‐PS‐PMMA‐PCL. Finally, the polymerization of tert‐butyl acrylate (tBA) via iniferter process gave the targeted H‐shaped block copolymer. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4601–4607     

Preparation and characterization of SBA‐15 supported iron(II)‐bisimine pyridine catalyst for ethylene polymerization

2,6‐Diacetylpyridinebis (2,6‐diisopropylani) iron dichloride, a late‐transition metal catalyst for olefin polymerization, was supported on SBA‐15 successfully and the property of the supported catalyst was carefully studied. Ethylene polymerization was systematically investigated in the presence of MAO under various conditions employing this type of catalyst system. In general, after support, a decrease in the catalytic activity was observed and higher molecular weight and fibrous morphology of polyethylene were obtained. The “extrusion polymerization” phenomenon was observed in ethylene polymerization by using the supported catalyst system. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4830–4837, 2004     

Preparation of a copolymer of methyl methacrylate and 2‐(dimethylamino)ethyl methacrylate with pendant 4‐benzyloxy‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy and its initiation of the graft polymerization of styrene by a controlled radical mechanism

The macroinitiator of a copolymer (PMD_BTM) of methyl methacrylate (MMA) and 2‐(dimethylamino)ethyl methacrylate (DAMA) with 4‐benzyloxy‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy (BTEMPO) pendant groups was prepared by the photochemical reaction of tertiary amine groups of the copolymer with benzophenone in the presence of BTEMPO. The radical copolymerization of MMA and DAMA was carried out first with azo‐bis‐isobutyronitrile (AIBN) as an initiator; then, the dimethylamine groups of the copolymer constituted a charge‐transfer complex with benzophenone under UV irradiation, and the methylene of ternary amine and diphenyl methanol radicals were produced. The former was capped by BTEMPO, and the nitroxide (BTEMPO) was attached to the polymeric backbone. The amount of pendant BTEMPO on PMD_BTM was measured by ¹H NMR. PMD_BTM initiated the graft polymerization of styrene via a controlled radical mechanism, and the molecular weight of the PMD‐g‐polystyrene increased with the polymerization time. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 604–612, 2001     

Simple route for synthesis of H‐shaped copolymers

The H‐shaped copolymers, [poly(L ‐lactide)]₂polystyrene [poly(L ‐lactide)]₂, [(PLLA)₂PSt(PLLA)₂] have been synthesized by combination of atom transfer radical polymerization (ATRP) with cationic ring‐opening polymerization (CROP). The first step of the synthesis is ATRP of St using α,α′‐dibromo‐p‐xylene/CuBr/2,2′‐bipyridine as initiating system, and then the PSt with two bromine groups at both chain ends (Br–PSt–Br) were transformed to four terminal hydroxyl groups via the reaction of Br–PSt–Br with diethanolamine in N,N‐dimethylformamide. The H‐shaped copolymers were produced by CROP of LLA, using PSt with four terminal hydroxyl groups as macroinitiator and Sn(Oct)₂ as catalyst. The copolymers obtained were characterized by ¹H NMR spectroscopy and gel permeation chromatography. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2794–2801, 2006     

Ethylene polymerization by bis(salicylaldiminate)nickel(II)/aluminoxane catalysts

The homopolymerization of ethylene by using different catalytic systems based on dinitro‐substituted bis(salicylaldiminate)nickel(II) precursors such as bis[3,5‐dinitro‐N(2,6‐diisopropylphenyl)]nickel(II) and bis[3,5‐dinitro‐N(phenyl)]nickel(II) in combination with organoaluminum compounds was investigated. In particular, the catalytic performances were studied as a function of the main reaction parameters, such as temperature, pressure, Al/Ni molar ratio, and duration. Methylaluminoxane resulted in the best co‐catalyst. Activities up to 200 kg polyethylene/(mol Ni × h) to give a linear high‐molecular‐weight polymer were achieved. The influence of the bulkiness of the substituents on the N‐aryl group of the aldimine ligand was also checked; it resulted in a determinant for catalytic activity rather than for polymer characteristics. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2534–2542, 2004