Unimodal Molecular Weight Distribution Research Articles

Synthesis of vanadium(iii) complexes bearing iminopyrrolyl ligands and their role as thermal robust ethylene (co)polymerization catalysts

Bis(imino)pyrrolyl vanadium(III) complexes 2a-e [2,5-C(4)H(2)N(CH=NR)(2)]VCl(2)(THF)(2) [R = C(6)H(5) (2a), 2,6-Me(2)C(6)H(3) (2b), 2,6-(i)Pr(2)C(6)H(3) (2c), 2,4,6-Me(3)C(6)H(2) (2d), C(6)F(5) (2e)] and bis(iminopyrrolyl) vanadium(III) complex 4f [C(4)H(3)N(CH=N-2,6-(i)PrC(6)H(3))](2)VCl(THF) have been prepared in good yields from VCl(3)(THF)(3) by treating with 1.0 and 2.0 equivalent deprotonated ligands in tetrahydrofuran (THF), respectively. These complexes were characterized by FTIR and mass spectra as well as elemental analysis. Structures of 2c and 4f were further confirmed by X-ray crystallographic analysis. DFT calculations indicated the configurations of 2a-e with two nitrogen atoms of the chelating ligand coordinating with vanadium metal centre were more stable in energy. These complexes were employed as catalysts for ethylene polymerization at various reaction conditions. On activation with Et(2)AlCl, these complexes exhibited high catalytic activities (up to 22.2 kg mmol(-1)(V) h(-1) bar(-1)) even at high temperature, suggesting these catalysts possessed remarkable thermal stability. Moreover, high molecular weight polymer with unimodal molecular weight distributions can be obtained, indicating the polymerization took place in a single-site nature. The copolymerizations of ethylene and 1-hexene with precatalysts 2a-e and 4f were also explored in the presence of Et(2)AlCl. Catalytic activity, comonomer incorporation, and properties of the resultant polymers can be controlled over a wide range by tuning catalyst structures and reaction parameters.

Amphiphilic Block‐Graft Copolymers with a Degradable Backbone and Polyethylene Glycol Pendant Chains Prepared via Ring‐Opening Polymerization of a Macromonomer

Well-defined amphiphilic block-graft copolymers PCL-b-[DTC-co-(MTC-mPEG)] with polyethylene glycol methyl ether pendant chains were designed and synthesized. First, monohydroxyl-terminated macroinitiators PCL-OH were prepared. Then, ring-opening copolymerization of 2,2-dimethyltrimethylene carbonate (DTC) and cyclic carbonate-terminated PEG (MTC-mPEG) macromonomer was carried out in the presence of the macroinitiator in bulk to give the target copolymers. All the polymers were characterized by (1) H NMR and gel permeation chromatography (GPC). The polymers have unimodal molecular weight distributions and moderate polydispersity indexes. The amphiphilic block-graft copolymers self-assemble in water forming stable micelle solutions with a narrow size distribution.

Bis(β‐enaminoketonato) vanadium (III or IV) complexes as catalysts for olefin polymerization

AbstractBis(β‐enaminoketonato) vanadium(III) complexes (2a–c) [O(R1)CC(H)xC(R2)NC6H5]2VCl(THF) and the corresponding vanadium(IV) complexes (3a–c) [O(R1)CC(H)xC(R2) NC6H5]2VO (R1 = (CH2)4, R2 = H, x = 0, a; R1 = C6H5, R2 = H, x = 1, b; R1 = C6H5, R2 = C6H5, x = 1, c) have been synthesized from VCl3(THF)3 and VOCl2(THF)2, respectively, by treating with 2.0 equivalent β‐enaminoketonato ligands in tetrahydrofuran. Structures of 2b and 3a–c were further confirmed by X‐ray crystallographic analysis. The complexes were investigated as the catalysts for ethylene polymerization in the presence of Et2AlCl. Complexes 2a–c and 3a–c exhibited high catalytic activities (up to 23.76 kg of PE/mmolV h bar), and afforded polymers with unimodal molecular weight distributions at 70 °C indicating the good thermal stability. The catalytic behaviors were influenced not only by the oxidation state of the catalyst precursors but also by the ligand structures. Complexes 2a–c and 3a–c were also effective catalyst precursors for ethylene/1‐hexene copolymerization. The influence of polymerization parameters such as reaction temperature, Al/V molar ratio and hexene feed concentration on the ethylene/hexene copolymerization behaviors have bee also investigated in detail. In addition, the agents such as AlMe3, AliBu3, MeMgBr, MgCl2, and ZnEt2 were applied to control the molecular weight and molecular weight distribution modal. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3062–3072, 2010

Synthesis of novel poly(ethylene-ter-1-hexene-ter-dicyclopentadiene)s using bis(β-enaminoketonato)titanium catalysts and their applications in preparing polyolefin-graft-poly(ɛ-polycaprolactone)

Novel terpolymers containing ethylene, 1-hexene and dicyclopentadiene (DCPD) were synthesized using bis(β-enaminoketonato)titanium catalysts [PhNC(R2)CHC(R1)O]2TiCl2 (1a: R1 = Ph, R2 = CF3; 1b: R1 = CF3, R2 = CH3). In the presence of modified methylaluminoxane, these catalysts afforded terpolymers with a broad range of monomer compositions and unimodal molecular weight distributions. 13C NMR spectra reveal the exclusive insertion manner of DCPD maintained under various reaction conditions. DSC results show the melting temperature and the glass transition temperature are very sensitive to the terpolymer composition and the morphology can be easily tuned from semicrystalline state to amorphous state. With ethylene/1-hexene/DCPD molar ratio about 67/28/5, the terpolymer exhibits low glass transition temperature (Tg = −50 °C) and has a great potential to serve as polyolefin elastomer. Additionally, the terpolymer containing 4.3 mol% 1-hexene and 1.6 mol% DCPD was served as the “reactive intermediate polyolefin” for PCL graft reaction. The composition of graft copolymer was well controllable and high graft efficiency was observed. The microscopy studies in conjunction with the tensile tests revealed that PCL graft copolymer is the effective compatibilizer for polyethylene/polar polymer blends by improving the interfacial adhesion between separated phases.

Three-dimensional excitation emission matrix fluorescence spectroscopy and gel-permeating chromatography to characterize extracellular polymeric substances in aerobic granulation

Three-dimensional excitation emission matrix (EEM) fluorescence spectroscopy and gel-permeating chromatography (GPC) were employed to characterize the extracellular polymeric substances (EPS) in aerobic granulation. EPS matrix in this study was stratified into four fractions: (1) supernatant, (2) slime, (3) loosely bound EPS (LB-EPS), and (4) tightly bound EPS (TB-EPS). The results showed that the dissolved organic carbon was mainly distributed in TB-EPS fraction, and increased with increasing the operating time. The supernatant, slime, and LB-EPS fractions exhibited four fluorescence peaks, an autochthonous signature, unimodal MW distribution and lower molecular weight (MW) (3 < log [MW]<5), whereas the TB-EPS fraction only had two peaks, an allochthonous signature, multiple peaks and higher MW (5 < log [MW]<7). It was deemed that the formation of aerobic granules was correlated with the accumulation of proteins in the TB-EPS fraction. EEM spectroscopy and GPC profiles could be used as appropriate and effective methods to characterize the EPS in aerobic granulation from a micro-view level.

A new approach to controlled/living radical polymerization by DPE method

Controlled free radical polymerizations of methyl methacrylate and styrene in bulk by 1,1-diphenylethene (DPE) were demonstrated in a two-step process, preheating treatment of initiators followed by a living polymerization of monomers. Over the course of polymerization, continuous growing of polymers with unimodal molecular weight distribution and a relatively small polydispersity index (around 1.5 even in the range of Mn∼105g/mol) on GPC diagrams was observed. In our previous study, the DPE controlled radical polymerization with constant molecular weight throughout the polymerization was caused by the intrinsically low reactivation rate constant (k2) of DPE capped dormant chains. To raise the reaction temperature in order to increase k2, a continuous molecular weight growing but broader or bimodal molecular weight distribution was obtained if the living polymerization was conducted in a one-step process. In this work, a two-step polymerization process was proposed. In the first step, the initiator 2,2′-azobisisobutyronitrile (AIBN), control agent DPE, and small amount of monomer were mixed and heated for a specific time period. Then a living polymerization of monomers was conducted in the second step of polymerization. This two-step new approach had minimized the imperfections of the DPE system; thus the polymerization showed better living characters and revealed its enhanced control abilities.

Poly( p-maleimidostyrene) as a macromolecule initiator for polymerization of styrene-type monomers – Synthesis of block copolymers containing poly( p-maleimidostyrene) with highly reactive pendent maleimido groups

4-Substituted styrenes (substituent: methoxy, methyl, acetoxy, maleimido and none), were cationically polymerized with an initiator system involving poly( p-maleimidostyrene)(PMS) as a macroinitiator, having highly reactive pendent maleimide moieties and a α-chlorobenzyl structure at the polymer end. Using PMS/SnCl 4/tetra- n-butylammmonium chloride initiator system, block copolymers of 4-substituted styrenes onto PMS were obtained in CH 2Cl 2 at 0 °C. As for the polymerization of N-(4-vinylphenyl)maleimide and 4-acetoxystyrene, especially, PMS as the macroinitiator was almost completely utilized for initiation reaction and the polymers having PMS- b-poly(4-substituted styrene) platform with very narrow and unimodal molecular weight distribution were formed in contrast with the case of using 4-methoxystyrene and 4-methylstyrene with stronger electron releasing groups, in which the molecular weight distributions of the formed polymeric materials appeared to be bimodal.

Anomalous Melt Rheological Properties of Unimodal-MWD HDPE Blends

The melt rheological behaviors in both linear and nonlinear regions were studied for binary blends of high-density polyethylenes (HDPEs) with unimodal molecular weight distribution (MWD). The surface distortion of the component resin with high-molecular-weight (HMW) and wide MWD through the capillary die could be alleviated with the addition of the component resin with low-molecular-weight (LMW) and narrow MWD. At the concentration of LMW component resin above 50 wt%, the negative deviation behavior (NDB) was observed in both the plots of dynamic storage modulus and complex viscosity versus the composition of the blends, furthermore, the Cole-Cole plot of the blend was below that of the pure LMW component, indicating the characteristics of immiscibility. However, the characteristic of homogeneity was revealed in the logG′∼logG″ curves that possessed almost identical slopes for all the blends. The anomalous phenomena were attributed to the slow diffusion of HMW ingredients in the blends, which was aggravated by the inefficient stress transfer during melt blending at high concentration of LMW component.

Synthesis, structure and ethylene (co)polymerization behavior of new nonbridged half-metallocene-type titanium complexes based on bidentate β-enaminoketonato ligands

A series of novel half-metallocene-type titanium complexes CpTiCl2[PhNC(R2)CHC(R1)O] (2a, R1 = Cy, R2 = CF3; 2b, R1 = tBu, R2 = CF3; 2c, R1 = Ph, R2 = CF3; 2d, R1 = Ph, R2 = CH3) have been synthesized by treating CpTiCl3 with the corresponding bidentate β-enaminoketonato ligands PhNC(R2)CHC(R1)OH in the presence of triethylamine. Single crystal X-ray diffraction revealed that complex 2b adopts distorted square-pyramid geometry around the titanium center. The complexes 2a–d were investigated as the catalysts for ethylene polymerization and the copolymerization of ethylene with norbornene. All the complexes were active towards ethylene (co)polymerization in the presence of modified methylaluminoxane, and produced high molecular weight (co)polymers. The catalytic activity and the norbornene incorporation were highly dependent upon catalyst and reaction conditions employed. Among four complexes, 2c exhibited both high catalytic activity and efficient norbornene incorporation under the same conditions, affording high molecular weight copolymers with unimodal molecular weight distributions.

Facile, efficient functionalization of polyethylene via regioselective copolymerization of ethylene with cyclic dienes

AbstractThe copolymerizations of ethylene with cyclic dienes [dicyclopentadiene (DCPD) and 2,5‐norbornadiene (NBD)] using bis(β‐enaminoketonato)titanium complexes [PhN = C(R2)CHC(R1)O]2TiCl2 (1a: R1 = CF3, R2 = CH3; 1b: R1 = t‐Bu, R2 = CF3; 1c: R1 = Ph, R2 = CF3) have been investigated. In the presence of modified methylaluminoxane, these complexes exhibited high catalytic activities in the copolymerization of ethylene with DCPD or NBD, affording high molecular weight copolymers with unimodal molecular weight distributions. 1H and 13C‐NMR spectra reveal ethylene/DCPD copolymerizations by catalysts 1a–c proceeds through the enchainment of norbornene ring. Catalysts 1a and 1c showed a tendency to afford alternating copolymers. More noticeably, catalysts 1b and 1c bearing bulky substituents on the ligands promote ethylene/NBD copolymerization without crosslinking, affording the copolymer containing intracyclic double bonds. The NBD incorporation as high as 27.2 mol % has been achieved by catalyst 1c. Moreover, the microstructures of the copolymers were further confirmed by the measurement of reactivity ratios and dyad monomer sequences as well as mean sequence lengths. The intracyclic double bonds of ethylene/DCPD or ethylene/NBD copolymers can be fully converted into polar groups such as epoxy, amine, silane, and hydroxyl groups under mild conditions. Convenient synthesis of hydroxylated polyethylene can be provided for the first time through the ring opening reaction of epoxide. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1764–1772, 2010

An Expeditious Multigram‐Scale Synthesis of Lysine Dendrigraft (DGL) Polymers by Aqueous N‐Carboxyanhydride Polycondensation

The synthesis and characterisation of new arborescent architectures of poly(L-lysine), called lysine dendrigraft (DGL) polymers, are described. DGL polymers were prepared through a multiple-generation scheme (up to generation 5) in a weakly acidic aqueous medium by polycondensing N(epsilon)-trifluoroacetyl-L-lysine-N-carboxyanhydride (Lys(Tfa)-NCA) onto the previous generation G(n-1) of DGL, which was used as a macroinitiator. The first generation employed spontaneous NCA polycondensation in water without a macroinitiator; this afforded low-molecular-weight, linear poly(L-lysine) G1 with a polymerisation degree of 8 and a polydispersity index of 1.2. The spontaneous precipitation of the growing N(epsilon)-Tfa-protected polymer (GnP) ensures moderate control of the molecular weight (with unimodal distribution) and easy work-up. The subsequent alkaline removal of Tfa protecting groups afforded generation Gn of DGL as a free form (with 35-60% overall yield from NCA precursor, depending on the DGL generation) that was either used directly in the synthesis of the next generation (G(n+1)) or collected for other uses. Unprotected forms of DGL G1-G5 were characterised by size-exclusion chromatography, capillary electrophoresis and (1)H NMR spectroscopy. The latter technique allowed us to assess the branching density of DGL, the degree of which (ca. 25%) turned out to be intermediate between previously described dendritic graft poly(L-lysines) and lysine dendrimers. An optimised monomer (NCA) versus macroinitiator (DGL G(n-1)) ratio allowed us to obtain unimodal molecular weight distributions with polydispersity indexes ranging from 1.3 to 1.5. Together with the possibility of reaching high molecular weights (with a polymerisation degree of ca. 1000 for G5) within a few synthetic steps, this synthetic route to DGL provides an easy, cost-efficient, multigram-scale access to dendritic polylysines with various potential applications in biology and in other domains.

Vanadium(V) complexes containing tetradentate amine trihydroxy ligands as catalysts for copolymerization of cyclic olefins

AbstractA series of vanadium(V) complexes bearing tetradentate amine trihydroxy ligands [NOOO], which differ in the steric and electronic properties, have been synthesized and characterized. Single crystal X‐ray analysis showed that these complexes are five or six coordinated around the vanadium center in the solid state. Their coordination geometries are octahedral or trigonal bipyramidal. In the presence of Et2AlCl, these complexes have been investigated as the efficient catalysts for ethylene polymerization and ethylene/norbornene copolymerization at elevated reaction temperature and produced the polymers with unimodal molecular weight distributions (MWDs), indicating the single site behaviors of these catalysts. Both the steric hindrance and electronic effect of the groups on the tetradentate ligands directly influenced catalytic activity and the molecular weights of the resultant (co)polymers. Other reaction parameters that influenced the polymerization behavior, such as reaction temperature, ethylene pressure, and comonomer concentration, are also examined in detail. Furthermore, high catalytic activities of up to 3.30 kg polymer/mmolV·h were also observed when these complexes were applied to catalyze the copolymerization of ethylene and 5‐norbornene‐2‐methanol, producing the high‐molecular‐weight copolymers (Mw = 157–400 kg/mol) with unimodal MWDs (Mw/Mn = 2.5–3.0) and high polar comonomer incorporations (up to 12.3 mol %). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1122–1132, 2010

Cationic polymerization in rotating packed bed reactor: Experimental and modeling

AbstractOn the basis of analysis of key engineering factors predominating in cationic polymerization, butyl rubber (IIR) as an example was synthesized by cationic polymerization in the high‐gravity environment generated by a rotating packed bed (RPB) reactor. The influence of the rotating speed, packing thickness, and polymerization temperature on the number average molecular weight (Mn) of IIR was studied. The optimum experimental conditions were determined as rotating speed of 1200 r min−1, packing thickness of 40 mm and polymerization temperature of 173 K, where IIR with Mn of 289,000 and unimodal molecular weight distribution of 1.99 was obtained. According to the experimental results and elementary reactions, a model for the prediction of Mn was developed, and the validity of the model was confirmed by the fact that most of the predicted Mns agreed well with the experimental data with a deviation within 10%. © 2009 American Institute of Chemical Engineers AIChE J, 2010

1-Hexene polymerization by Cp*TiX 2(O-2,6- iPr 2C 6H 3) [X: Cl, Me] in the presence of MAO- and MMAO-modified carbonaceous supports

Various MAO-, MMAO-modified carbonaceous materials with different degrees of coalification, surface areas and amounts of nitrogen in their structures have been prepared, and the nature of Al supported and their compositions of elements close to surface were determined by the XPS method. These materials were effective as supported cocatalysts in 1-hexene polymerization using Cp*TiX 2(O-2,6- i Pr 2C 6H 3) [X = Cl ( 1), Me ( 2)], affording poly(1-hexene)s with unimodal molecular weight distributions; the facts clearly suggest that these polymerizations proceeded with uniform (single-site) catalytically active species. The activities were affected by the nature of the carbonaceous supports employed, whereas the surface area does not strongly affect the activity in this catalysis.

Polymerization of (meth)acrylates with aluminum-based initiators

A simple and effective way to prepare poly(acrylate)s, such as poly(methacrylate), poly(butyl acrylate) and poly(butyl methacrylate), has been achieved by using the single component aluminum-based compounds, such as modified methylaluminoxane (MMAO), triisobutylaluminium (TIBA) and triethylaluminium (TEA) as initiators. Effective initiations and high molecular weight polymers with unimodal molecular weight distributions could be easily obtained by varying the reaction parameters of systems under mild conditions. Although these aluminum compounds were inefficient initiators for methyl methacrylate (MMA) polymerization, they exhibited remarkable catalytic activity for butyl methacrylate (BMA) polymerization, affording high molecular weight poly(BMA)s.

Synthesis and characterization of para-nitro substituted 2,6-bis(phenylimino)pyridyl Fe(II) and Co(II) complexes and their ethylene polymerization properties

Four iron(II) and cobalt(II) complexes ligated by 2,6-bis(4-nitro-2,6-R 2-phenylimino)pyridines, LMCl 2 ( 1: R = Me, M = Fe; 2: R = iPr, M = Fe; 3: R = Me, M = Co; 4: R = iPr, M = Co) have been synthesized and fully characterized, and their catalytic ethylene polymerization properties have been investigated. Among these complexes, the iron(II) pre-catalyst bearing the ortho-isopropyl groups (complex 2) exhibited higher activities and produced higher molecular weight polymers than the other complexes in the presence of methylaluminoxane (MAO). A comparison of 2 with the reference non-nitro-substituted catalyst (2,6-bis(2,6-diisopropylphenylimino)pyridyl)FeCl 2 (FeCat 5) revealed a modest increase of the catalytic activity and longer lifetime upon substitution of the para-positions with nitro groups (activity up to 6.0 × 10 3 kg mol −1 h −1 bar −1 for 2 and 4.8 × 10 3 kg mol −1 h −1 bar −1 for 5), converting ethylene to highly linear polyethylenes with a unimodal molecular weight distribution around 456.4 kg mol −1. However, the iron(II) pre-catalyst 1 on changing from ortho-isopropyl to methyl groups displayed much lower activities (over an order of magnitude) than 2 under mild conditions. As expected, the cobalt analogues showed relatively low polymerization activities.

Efficient Synthesis of Functionalized Polyolefin by Incorporation of 4-Vinylcyclohexene in Ethylene Copolymerization Using Half-Titanocene Catalysts

Copolymerizations of ethylene with vinylcyclohexene (VCHen) by using Cp′TiCl2(X) [X = O-2,6-iPr2C6H3, Cp′ = Cp* (1); X = N═CtBu2, Cp′ = Cp* (2) and Cp (3)] catalyst systems with MAO have been explored. The copolymerizations proceeded via vinyl addition/insertion affording high molecular weight copolymers containing cyclohexenyl side chains (with uniform compositions as well as with unimodal molecular weight distributions) accompanied with certain degree of side reaction (intramolecular cyclization after VCHen insertion). Degree of the side reaction (cyclization) was dependent upon the catalyst employed, polymerization temperature, but was not affected by the time course, the Al/Ti molar ratios. The Cp−ketimide analogue (3) showed the best catalyst performance in terms of both the catalytic activity and the selectivity (lowest degree of the subsequent intramolecular cyclization) in the copolymerization. Quantitative epoxidation of the olefinic double bonds in the resultant copolymer has been achieved by us...

Synthesis of All-Trans High Molecular Weight Poly(N-alkylcarbazole-2,7-vinylene)s and Poly(9,9-dialkylfluorene-2,7-vinylene)s by Acyclic Diene Metathesis (ADMET) Polymerization Using Ruthenium−Carbene Complex Catalysts

Syntheses of poly(9,9-dialkylfluorene-2,7-vinylene)s (PFVs, alkyl = n-hexyl, n-octyl, 2′-ethylhexyl) and poly(N-alkylcarbazole-2,7-vinylene)s (PCVs, alkyl = n-octyl, 9′-heptadecanyl) by acyclic diene metathesis (ADMET) polymerization using Ru−carbene complexes have been explored. The polymerizations in the presence of Ru(CHPh)(Cl)2(IMesH2)(PCy3) and Ru(CH-2-OiPr-C6H4)(Cl)2(IMesH2) [Cy = cyclohexyl, IMesH2 = 1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene] afforded relatively high molecular weight PFVs, PCV (alkyl = 9′-heptadecanyl) with unimodal molecular weight distributions, and the olefinic double bonds in the resultant polymers possessed highly trans regularity in all cases. The resultant defect-free PFVs possessed higher absolute quantum yields (Φ = 92−99%) than those reported previously, whereas no significant differences in the UV−vis and the fluorescent spectra (absorption bands, peak maxima) in the resultant PFVs were observed as an effect of alkyl side chain in the 9-position. The UV−vis an...

Ethylene polymerization and ethylene/hexene copolymerization with vanadium(III) catalysts bearing heteroatom‐containing salicylaldiminato ligands

AbstractA series of novel vanadium(III) complexes bearing heteroatom‐containing group‐substituted salicylaldiminato ligands [RNCH(ArO)]VCl2(THF)2 (Ar = C6H4, R = C3H2NS, 2a; C7H4NS, 2c; C7H5N2, 2d; Ar = C6H2tBu2 (2,4), R = C3H2NS, 2b) have been synthesized and characterized. Structure of complex 2c was further confirmed by X‐ray crystallographic analysis. The complexes were investigated as the catalysts for ethylene polymerization in the presence of Et2AlCl. Complexes 2a–d exhibited high catalytic activities (up to 22.8 kg polyethylene/mmolV h bar), and affording polymer with unimodal molecular weight distributions at 25–70 °C in the first 5‐min polymerization, whereas produced bimodal molecular weight distribution polymers at 70 °C when polymerization time prolonged to 30 min. The catalyst structure plays an important role in controlling the molecular weight and molecular weight distribution of the resultant polymers produced in 30 min polymerization. In addition, ethylene/hexene copolymerizations with catalysts 2a–d were also explored in the presence of Et2AlCl, which leads to the high molecular weight and unimodal distributions copolymers with high comonomer incorporation. Catalytic activity, comonomer incorporation, and polymer molecular weight can be controlled over a wide range by the variation of catalyst structure and the reaction parameters, such as comonomer feed concentration, polymerization time, and polymerization reaction temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3573–3582, 2009

Copolymerization of Ethylene with α-Olefins Containing Various Substituents Catalyzed by Half-Titanocenes: Factors Affecting the Monomer Reactivities

Ethylene copolymerizations with various pentenes [1-pentene, 4-methyl-1-pentene (4M1P), 3-methyl-1-pentene (3M1P), 4,4-dimethyl-1-pentene (NHEP)] using Cp*TiCl2(O-2,6-iPr2C6H3) (1), CpTiCl2(N═ CtBu2) (2), [Me2Si(C5Me4)(NtBu)]TiCl2 (4) − MAO catalyst systems have been explored. Both 1 and 2 exhibited high catalytic activities affording high molecular weight copolymers with unimodal molecular weight distributions; the rErC values (rE = kEE/kEC; E = ethylene; C = comonomer) by 1 were small, suggesting that the monomer incorporations were rather alternating, whereas the copolymerization by 4 proceeded in a random manner (rErC = ca. 1) except the copolymerization with 3M1P. 1 exhibited remarkable both catalytic activities and 3M1P incorporation in the ethylene/3M1P copolymerization, and the rE value (8.73) was much smaller than that by 4 (92), 2 (28.3). Both 1 and 4 showed better NHEP incorporations than 2 in the ethylene/NHEP copolymerization, and the rather large rE value by 2 (6.77) compared to those by 1 (2.58−2.94) was also obtained in the copolymerization with 4M1P. These results clearly indicate that the monomer reactivities (rE values) are influenced not only by the substituent in the olefins, but also by the nature of the catalytically active species (structure, and ligand set employed). Both 1 and 2 also exhibited notable catalytic activities in the copolymerization of ethylene with 1-dodecene, 1-hexadecene, affording high molecular weight copolymers with unimodal molecular weight distributions. No notable differences toward the rE values by 1,2,4 were seen, although the values were slightly affected by both the steric bulk of olefins (linear branching) and the catalyst structure employed.