A series of novel (arylimido)vanadium(V) complexes bearing tridentate salicylaldiminato chelating ligands, V(N-2,6-Me₂C₆H₃)Cl₂[(O-2-^tBu-4-R-C₆H₃)CHND] (R = H, D = 2-CH₃OC₆H₄ (2a); 2-CH₃SC₆H₄ (2b); 2-Ph₂PC₆H₄ (2c); 8-C₉H₆N (quinoline) (2d); CH₂C₅H₄N (2e); R = ^tBu, D = 2-Ph₂PC₆H₄ (2f)), were prepared from V(NAr)Cl₃ by reacting with 1.0 equiv of the ligands in the presence of triethylamine in tetrahydrofuran. These complexes were characterized by ¹H, ¹³C, ³¹P, and ⁵¹V NMR spectra and elemental analysis. The structures of 2c and 2f were further confirmed by X-ray crystallographic analysis. These (arylimido)vanadium(V) complexes are effective catalyst precursors for ethylene polymerization in the presence of Et₂AlCl as a cocatalyst and ethyl trichloroacetate as a reactivating agent. Complex 2c with a PPh₂ group in the sidearm was found to exhibit an exceptional activity up to 133800 kg polyethylene/mol_V h for ethylene polymerization at 75 °C, which is one of the highest activities displayed by homogeneous vanadium(V) catalysts at high temperature. Moreover, high molecular weight polymers with unimodal molecular weight distribution can be obtained, indicating the single site behavior of these catalysts. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2633-2642

Novel cyclic olefin polymers (COPs) derived from bulky cyclic olefin, exo-1,4,4a,9,9a,10-hexahydro-9,10(1′,2′)-benzeno-l,4-methanoanthracene (HBMN), with high glass transition temperature (T_g), excellent thermal stability, high transparency, and improved mechanical performance, have been achieved by ring-opening metathesis polymerization and subsequent hydrogenation. The “first-generation Grubbs” catalyst, RuCl₂(PCy₃)₂(CHPh) (Cy = cyclohexyl) (G1), displays very high activity for homo/copolymerization with complete conversion. Homopolymer of the HBMN after complete hydrogenation showed a highest T_g of 223.6 °C. Copolymerization of HBMN with tricyclo[4.3.0.12,5]deca-3-ene or 5-n-hexylnorbornene was also carried out. These two series of COPs were characterized by gel permeation chromatography, nuclear magnetic resonance, differential scanning calorimetry, and thermogravimetric analysis. The T_g of the resulted COPs linearly increased with HBMN content, which is easily controlled by changing feed ratios. The tensile test indicates that these copolymers have good mechanical performance as all these copolymers show a higher strain at break compared with commercial products (TOPAS^®). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2654-2661

Novel cyclic olefin polymers (COPs) with excellent transparency and high glass-transition temperature (T_g) synthesized from bulky norbornene derivative, exo-1,4,4a,9,9a,10-hexahydro-9,10(1',2')-benzeno-l,4-methanoanthracene (HBMN), and cis-cyclooctene (COE) by ring-opening metathesis copolymerization utilizing the “first-generation Grubbs” catalyst, RuCl₂(PCy₃)₂(CHPh), and subsequent hydrogenation was reported herein. To get amorphous copolymers, it was of great importance to control the feed ratios and the polymerization time for gradient copolymerization. All these copolymers showed very high T_gs (141.1–201.2 °C), which varied with the content of HBMN. The films of the gradient copolymers with only one T_g were highly transparent. On the contrary, all the block copolymers synthesized through sequential addition showed two thermal transition temperatures, T_g and melt temperature (T_m), and the films of these block copolymers were opaque. The mechanical performances of the COPs were also investigated. It is the first report that transparent COP could be prepared from bulky norbornene derivative and monocyclic olefin. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3240–3249

This article discussed the root causes of the interesting differences between rac-Et(Ind)₂ZrCl₂ and dimethyl (pyridyl-amido)hafnium in catalyzing the propylene/ω-halo-α-alkene copolymerization. Confirmed by density functional theory (DFT) calculations, the larger spacial opening around the active center of rac-Et(Ind)₂ZrCl₂ contributes to the coordination and insertion of the monomers, resulting in the higher catalytic activity, while the narrow spacial opening around the Hf center retards the chain transfer reaction, leading to the much higher molecular weights (M_ws) of the copolymers. The superior tolerability of Zr catalyst toward halogen groups might be attributed to that the dormant species generated from halogen coordination could be promptly reactivated. DFT calculations indicated the higher probability for the ω-halo-α-alkene vinyl to coordinate with the Hf catalyst leading to the better ability to incorporate halogenated monomers. The high M_ws and the outstanding isotacticity achieved by the Hf catalyst determined the higher melting temperature values of the copolymers with a certain amount of halogen groups. In addition, the chain transfer schemes were employed to analyze why the presence of halogenated monomers greatly decreased the M_ws of the copolymers when rac-Et(Ind)₂ZrCl₂ was used, while had no or little effect upon the M_ws in the copolymerization by the Hf catalyst. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3421–3428

Hyperbranched polyesters with thioether linkages were facilely prepared from methyl 10-undecenoate, a castor oil-derived renewable chemical. The monomer was obtained in excellent yield through thiol–ene click chemistry in the presence of catalytic amounts of photoinitiator under UV irradiation. Subsequent bulk polycondensation via a transesterification process catalyzed by Ti(OBu)₄, Sb₂O₃ or Zn(OAc)₂ gave hyperbranched polyesters with high molecular weights and unusual crystalline properties. The degree of branching in the range 0.45 − 0.54 calculated from quantitative ¹³C NMR spectroscopy and low inherent viscosities of 0.16 − 0.25 dL g⁻¹ strongly confirmed the hyperbranched structures of the resultant polymers. © 2012 Society of Chemical Industry

A series of novel vanadium(III) complexes bearing tridentate phenoxy-phosphine [O,P,O] ligands and phosphine oxide-bridged bisphenolato [O,PO,O] ligands, which differ in the steric and electronic properties, have been synthesized and characterized. These complexes were characterized by Fourier transform infrared spectroscopy (FTIR) and mass spectra as well as elemental analysis. Single-crystal X-ray diffraction revealed that complexes 3c and 4e adopt an octahedral geometry around the vanadium center. In the presence of Et₂AlCl as a cocatalyst, these complexes displayed high catalytic activities up to 22.8 kg PE/mmol_V.h.bar for ethylene polymerization, and produced high-molecular-weight polymers. Introducing additional oxygen atom on phosphorus atom of [O,P,O] ligands has resulted in significant changes on the aspect of steric/electronic effect, which has an impact on polymerization performance. 3c and 4c/Et₂AlCl catalytic systems were tolerant to elevated temperature (70 °C) and yielded unimodal polyethylenes, indicating the single-site behavior of these catalysts. By pretreating with equimolar amounts of alkylaluminums, functional α-olefin 10-undecen-1-ol can be efficiently incorporated into polyethylene chains. 10-Undecen-1-ol incorporation can easily reach 14.6 mol % under the mild conditions. Other reaction parameters that influenced the polymerization behavior, such as reaction temperature, Al/V (molar ratio), and comonomer concentration, are also examined in detail. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

A series of novel cyclic olefin copolymers (COCs), including ethylene/tricyclo[4.3.0.1^2,5]deca-3-ene (TDE), ethylene/tricyclo[4.4.0.1^2,5]undec-3-ene (TUE), and ethylene/tricyclo[6.4.0.1^9,12]tridec-10-ene (TTE) copolymers, have been synthesized via effective copolymerizations of ethylene with bulk cyclic olefin comonomers using bis(β-enaminoketonato) titanium catalysts (1a [PhNC(CH₃)CHC(CF₃)O]₂TiCl₂; 1b: [PhNC(CF₃)CHC(Ph)O]₂TiCl₂). With modified methylaluminoxane as a cocatalyst, both catalysts exhibit high catalytic activities, producing high molecular weight copolymers with high comonomer incorporations and unimodal molecular weight distributions. The microstructures of obtained ethylene/COCs are established by combination of ¹H, ¹³C NMR, ¹³C DEPT, HSQC ¹H¹³C, and ¹H¹H COSY NMR spectra. DSC analyses indicate that the glass transition temperature (T_g) increases with the enhancement of comonomer volume (TDE < TUE < TTE). High T_g value up to 180 °C is easily attained in ethylene/TTE copolymer with the low content of 35.8 mol %. TGA analyses reveal that these copolymers all possess high thermal stability with degradation temperatures (T_d) higher than 370 °C in N₂ and air. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3144–3152

Hyperbranched vinyl polymers with high degrees of branching (DBs) up to 0.43 functionalized with numerous pendent allene groups have been successfully prepared via reversible addition fragmentation chain transfer polymerization of a state-of-art allene-derived asymmetrical divinyl monomer, allenemethyl methacrylate (AMMA). The gelation did not occur until high monomer conversions (above 90%), as a result of the optimized reactivity difference between the two vinyl groups in AMMA. The branched structure was confirmed by a combination of a triple-detection size exclusion chromatography (light scattering, refractive index, and viscosity detectors) and detailed ¹H NMR analyses. A two-step mechanism is proposed for the evolution of branching according to the dependence of molecular weight and DB on monomer conversion. Controlled radical polymerization proceeds until moderate conversions, mainly producing linear polymers. Subsequent initiation and propagation on the polymerizable allene side chains as well as the coupling of macromolecular chains generate numerous branches at moderate-to-high monomer conversions, dramatically increasing the molecular weight of the polymer. AMMA was also explored as a new branching agent to construct poly(methyl methacrylate)-type hyperbranched polymers by its copolymerization with methyl methacrylate. The DB can be effectively tuned by the amount of AMMA, showing a linear increase trend. The pendent allene groups in the side chains of the copolymers were further functionalized by epoxidation and thiol-ene chemistry in satisfactory yields. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2959–2969

Allene groups are first employed as the reactive moiety in the simple and efficient synthesis of well-defined functional polyethylene. By copolymerization of ethylene with allene group substituted norbornene, the allene group is successfully introduced into the polyethylene with a high content. The retained allene groups are demonstrated to be highly reactive in following photoinduced functionalized reactions and can be efficiently converted into the functional groups without the multi-step, time consuming processes that have generally been required in previous reports, providing the side group-functionalized polyethylene with a wide range of functional group content.

A new titanium complex [PhN=C(Ph)CHC(CF₃)O]₂TiCl₂ (2a), with an asymmetric β-enaminoketonato [N,O] ligand, has been synthesized and fully characterized. With modified methylaluminoxane as a cocatalyst, the behaviors of ethylene polymerization, and ethylene/α-olefin and ethylene/norbornene copolymerization have been explored in detail. Relative to its regioisomer 2b ([PhN=C(CF₃)CHC(Ph)O]₂TiCl₂), the present catalyst exhibits significant predominance. The catalytic activity in 2a-catalyzed homo- and copolymerization are much higher than those in 2b-catalyzed (co)polymerization. Furthermore, compared with 2b, catalyst 2a possesses an obviously stronger ability towards copolymerization, due to a wide coordination space caused by exchanging the position of the phenyl group and trifluoromethyl group on the framework.

A series of functional polyethylenes have been simply and efficiently synthesized via the combination of regioselective ethylene/5-vinyl-2-norbornene (VNB) copolymerization using [PhNC(CF₃)CHCO(Ph)]₂TiCl₂ catalyst and following ultraviolet light initiated thiol-ene click reaction. On treatment of ethylene/VNB copolymer with different thiols including mercaptoethanol, 1-thioglycerol, methyl mercaptoacetate, methyl mercaptopropionate, 2-mercaptoethylamine, mercaptoacetic acid, and mercaptopropanoic acid, various polar groups have been successfully introduced into the polyethylene. Except 2-mercaptoethylamine, the functionalizations are quite efficient with the degree of functionalization higher than 94%, which is independent of thiol structure and double bond content. The content of polar group in functional polyethylene can be tuned in a wide range of 0–30 mol %. Gel permeation chromatography profiles indicate all functional polyethylenes that have very high molecular weights (160–336 kg/mol) with homogeneous formation. Besides, systematic investigation of the influence of vinyl type and thiol structure on reactivity has been also carried out. By treatment of mercaptoethanol with different copolymers (ethylene/VNB, ethylene/5-ethylidene-2-norbornene, and ethylene/dicyclopentadiene copolymer), the order of vinyl reactivity can be summarized as terminal > internal > cyclic double bond. For different thiols, the reactivity has the sequence of SHCH₂COOH > SHCH₂COOCH₃ > SHCH₂CH₂COOH > SHCH₂CH₂COOCH₃ > SHCH₂CH(OH)CH₂OH > SHCH₂CH₂OH > SHCH₂CH₂NH₂, which is depended on the solubility and the electron-withdrawing inductive effect of polar group. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

The facile and efficient functionalization of polynorbornene has been achieved through direct copolymerization of norbornene (NB) with 5-norbornene-2-yl acetate (NBA) or 5-norbornene-2-methanol (NBM) using a series of β-ketiminato Ni(II)-Me pyridine complexes 1–4 (Scheme 2) in the presence of B(C₆F₅)₃. Remarkably, the monomer conversion could reach up to about 96% in 10 min in the NB/NBA copolymerization. The copolymers with wide NBA contents (3.3–38.4 mol %) were obtained by variation of reaction conditions. These copolymers have high molecular weights (MWs) (M_n = 41.8–144 kg/mol) and narrow MW distributions (M_w/M_n = 1.80–2.27). In the absence of alkyl aluminum compounds, a monomer conversion of 81% was observed in the NB/NBM copolymerization, and copolymers with NBM content in the range of 11.2–21.8 mol % were obtained by variation of reaction conditions. In addition, Ni(II)-Me pyridine complexes 2 was very active at a low B/Ni molar ratio of 6, while bis-ligand complex 6 bearing the same ligand just showed moderate efficiency at a high B/Ni molar ratio of 20. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

A series of C₁-symmetric titanium complexes with both salicylaldiminato and β-enaminoketonato as the ligands have been synthesized and investigated as the catalysts for propylene polymerization. In the presence of dried methylaluminoxane (dMAO), the complex with bulky substituent tert-butyl ortho to alkyl oxygen can promote living polymerization of propylene with improved catalytic activity at ambient temperature, producing high molecular weight syndiotactic polypropylenes (rrrr 90.2%) with narrow molecular weight distributions (M_w/M_n = 1.07–1.22), via a propagation of 1,2-insertion of monomer and chain-end control of stereoselectivity. The propagation of polymer chain is completely different from that mediated by FI catalysts (the titanium complexes with phenoxy-imine chelate ligands) which favor 2,1-insertion of monomer. The interaction between a fluorine and a β-hydrogen of a growing polymer chain, negligible chain transfer to monomer and dMAO without any free AlMe₃ were responsible for the achievement of living propylene polymerization. The substituent ortho to alkyl oxygen determined the stereo structure of the resultant polypropylene. In the case of less steric congested complexes with two nonequivalent coordination positions, the growing polymer chain might swing back to the favorite coordination position (site-epimerization), forming m dyads regioirregular units. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Vanadium(III) complexes bearing phenoxy-phosphine ligands (2a–g) (2-R₁-4-R₂-6-PPh₂-C₆H₂O)VCl₂(THF)₂ (2a: R₁ = R₂ = H; 2b: R₁ = F, R₂ = H; 2c: R₁ = Ph, R₂ = H; 2d: R₁ = tBu, R₂ = H; 2e: R₁ = R₂ = Me; 2f: R₁ = R₂ = tBu; 2g: R₁ = R₂ = CMe₂Ph) were prepared from VCl₃(THF)₃ by treating with 1.0 equiv of the ligand in tetrahydrofuran (THF) in the presence of excess triethylamine (TEA). The reaction of VCl₃(THF)₃ with 2.0 equiv of the ligand in THF in the presence of excess TEA afforded vanadium(III) complexes bearing two phenoxy-phosphine ligands (3c–f). These complexes were characterized by FTIR and mass spectrum as well as elemental analyses. Structures of 2f and 3c were further confirmed by X-ray crystallographic analyses. Complexes 2a–g and 3c–f were employed as the catalysts for ethylene polymerization under various reaction conditions. On activation with Et₂AlCl, these complexes exhibited high catalytic activities (up to 41.3 kg PE/mmol_V·h·bar) even at high temperature (70°C), and produced high molecular weight polymer with unimodal molecular weight distributions, indicating the polymerization took place in a single-site nature. Complexes 3c–f displayed better thermal stability than the corresponding complexes 2a–g under similar conditions. In addition, copolymerizations of ethylene and 1-hexene with precatalysts 2a–g were also explored in the presence of Et₂AlCl. Catalytic activity, comonomer incorporation, and properties of the resultant polymers can be controlled over a wide range by tuning catalyst structures and reaction parameters.© 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Iminopyrrolyl vanadium(III) complexes 2a–b bearing tridentate ligands [C₄H₃NCHNC₆H₄L]VCl₂(THF) [L = 2-P(C₆H₅)₂ (2a), 2-SMe (2b)] and complexes 2c–d with tetradentate ligands [(C₄H₃NCHN)₂R]VCl(THF) [R = 1,2-C₆H₄ (2c), 1,2-C₂H₄ (2d)] have been synthesized in high yields. With diethylaluminium chloride as a cocatalyst, complexes 2a–d were investigated as efficient catalysts for ethylene polymerization under various reaction conditions, and exhibited high catalytic activity and remarkable thermal stability. With these complexes, high molecular weight polymers with unimodal molecular weight distributions were obtained, indicating that the polymerization reaction took place in a single-site nature. Ethylene/1-hexene copolymerizations were also investigated in the presence of Et₂AlCl. Both increasing ligand denticity and introducing softer atom into the sidearm of the ligands significantly influenced catalytic activity, comonomer incorporation, and the molecular weights of the resultant polymers, suggesting that both the steric and the electronic effects of the ligands played an important role in adjusting chain propagation and transfer rate. The chain transfer mechanisms involved in the copolymerization process were investigated by carefully analyzing the microstructure of the copolymers. The signals of vinyl, disubstituted and tri-substituted vinylene double bond end groups were detected in the copolymer obtained by 2a/Et₂AlCl system but not in those by 2b–c/Et₂AlCl systems, indicating that bulky electron-donating group, P(C₆H₅)₂, may lead to those unusual transfer reactions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Two reactor blends of linear and branched polyethylene resins with bimodal molecular weight distributions were synthesized in a one-reactor polymerization process through the combination of 2,6-bis[1-(2,6-dimethyphenylimino)pyridyl]cobalt dichloride (1) and 2,3-bis(2,6-diisopropylphenyl)butanediimine nickel dibromide (2) or 1,2-bis(2,6-diisopropylphenyl)cyclohexene diimine nickel dibromide (3) in the presence of modified methylaluminoxane. The linear correlation between the catalyst activity and concentration of the nickel compounds suggested that the catalysts performed independently of one another. The molecular weights, molecular weight distributions, and crystalline and phase structures of the blends were investigated with a combination of high-temperature gel permeation chromatography, differential scanning calorimetry, wide-angle X-ray diffraction, and small-angle X-ray scattering techniques. The branching degree of the polyethylene produced with 3 was much higher than the branching degree of the sample produced with 2, although their molecular weights were relatively close. In addition, the crystallization rate, melting temperature, degree of crystallinity, and crystallization temperature of more highly branched blends produced with 1/3 were lower. The long periods and thickness of the crystalline region were greatly influenced by the addition of highly branched polyethylene. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

This article reports on a facile route for the preparation of methyl acrylate and methyl methacrylate graft copolymers via a combination of catalytic olefin copolymerization and atom transfer radical polymerization (ATRP). The chemistry first involved a transforming process from ethylene/allylbenzene copolymers to a polyolefin multifunctional macroinitiator with pendant sulfonyl chloride groups. The key to the success of the graft copolymerization was ascribed to a fast exchange rate between the dormant species and active radical species by optimization of the various experimental parameters. Polyolefin-g-poly(methyl methacrylate) and polyolefin-g-poly(methyl acrylate) graft copolymers with controlled architecture and various graft lengths were, thus, successfully prepared under dilute ATRP conditions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Bis(β-enaminoketonato) vanadium(III) complexes (2a–c) [O(R₁)CC(H)_xC(R₂)NC₆H₅]₂VCl(THF) and the corresponding vanadium(IV) complexes (3a–c) [O(R₁)CC(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/mmol_V 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

A series of novel hyperbranched poly(ester-amide)s (HBPEAs) based on neutral α-amino acids have been synthesized via the “AD + CBB′” couple-monomer approach. The ABB′ intermediates were stoichiometrically formed through thio-Michael addition reaction because of reactivity differences between functional groups. Without any purification, in situ self-polycondensations of the intermediates at elevated temperature in the presence of a catalyst afforded HBPEAs with multihydroxyl end groups. The degrees of branching (DBs) of the HBPEAs were estimated to be 0.40–0.58 and 0.24–0.54 by quantitative ¹³C NMR with two different calculation methods, respectively, depending on polymerization conditions and structure of monomers. The influences of catalyst, temperature, and intermediate structure on the polymerization process and molecular weights as well as properties of the resultant polymers were investigated. FTIR, NMR, and DEPT-135 NMR analyses revealed the branched structure of the resultant polymers. The HBPEAs possess moderately high molecular weights with broad distributions, glass transition temperatures in the range of −25.5 to 36.5 °C, and decomposition temperatures at 10% weight loss under nitrogen and air in the regions of 243.4–289.1 °C and 231.4–265.6 °C, respectively. Among them, those derived from D,L-phenylalanine display the lowest degree of branching, whereas the highest glass transition temperature and the best thermal stability. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Cu(0)-mediated living radical polymerization was first extended to acrylonitrile (AN) to synthesize polyacrylonitrile with a high molecular weight and a low polydispersity index. This was achieved by using Cu(0)/hexamethylated tris(2-aminoethyl)amine (Me₆-TREN) as the catalyst, 2-bromopropionitrile as the initiator, and dimethyl sulfoxide (DMSO) as the solvent. The reaction was performed under mild reaction conditions at ambient temperature and thus biradical termination reaction was low. The rapid and extensive disproportionation of Cu(I)Br/Me₆-TREN in DMSO/AN supports a mechanism consistent with a single electron transfer-living radical polymerization (SET-LRP) rather than activators generated by electron transfer atom transfer radical polymerization (AGET ATRP). ¹H NMR analysis and chain extension experiment confirm the high chain-end functionality of the resultant polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

A 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/mmol_V·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 (M_w = 157–400 kg/mol) with unimodal MWDs (M_w/M_n = 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

The 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

Novel chromium catalysts based on bidentate phenoxy-phosphinoyl (HO-2R₁-4R₂-6(Ph₂PO)C₆H₂: R₁ = R₂ = H, 3a; R₁ = tBu, R₂ = H, 3b; R₁ = R₂ = tBu, 3c; R₁ = R₂ = cumyl, 3d; R₁ = anthracenyl, R₂ = H, 3e) and thiophenol-phosphine (HS-2R₁-4R₂-6(Ph₂P)C₆H₂: R₁ = R₂ = H, 4a; R₁ = SiMe₃, R₂ = H, 4b) were prepared and characterized. Treatment with modified methyaluminoxane, these catalysts displayed moderate to high-catalytic activities for ethylene polymerization. The activities of them were higher than those of the corresponding catalysts based on bidentate phenoxy-phosphine ligands. Both the coordinated donors and the ortho-substituent of the ligands played an important role in improving catalytic activity. The effects of reaction parameters, such as cocatalyst and Al/Cr molar ratio as well as reaction temperature, on ethylene polymerization behaviors were investigated in detail for two favorable catalytic systems, 3b/CrCl₃(thf)₃ and 4b/CrCl₃(thf)₃. Catalyst 4b/CrCl₃(thf)₃ displayed higher catalytic activity and better temperature tolerance for ethylene polymerization than 3b/CrCl₃(thf)₃. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 311–319, 2010

Copolymerizations of ethylene with 5-vinyl-2-norbornene or 5-ethylidene-2-norbornene under the action of various titanium complexes bearing bis(β-enaminoketonato) chelate ligands of the type, [R¹NC(R²)CHC(R³)O]₂TiCl₂ (1, R¹=Ph, R²=CF₃, R³=Ph; 2, R¹=C₆H₄F-p, R²=CF₃, R³=Ph; 3, R¹=Ph, R²=CF₃, R³=t-Bu; 4, R¹=C₆H₄F-p, R²=CF₃, R³=t-Bu; 5, R¹=Ph, R²=CH₃, R³=CF₃; 6, R¹=C₆H₄F-p, R²=CH₃, R³=CF₃), have been shown to occur with the regioselective insertion of the endocyclic double bond of the monomer into the copolymer chain, leaving the exocyclic vinyl double bond as a pendant unsaturation. The ligand modification strongly affects the copolymerization behaviour. High catalytic activities and efficient co-monomer incorporation can be easily obtained by optimizing the catalyst structures and polymerization conditions.

A series of novel vanadium(III) complexes bearing heteroatom-containing group-substituted salicylaldiminato ligands [RNCH(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/mmol_V 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

A series of amino-pyrrolide ligands (1–4a) and their derivatives amino-thiophene ligand (5a), amino-indole ligand (6a) were prepared. Chromium catalysts, which were generated in situ by mixing the ligands with CrCl₃(thf)₃ in toluene, were tested for ethylene polymerization. The preliminary screening results revealed that the tridentate amino-pyrrolide ligands containing soft pendant donor, 3a, 4a/CrCl₃(thf)₃ systems displayed high catalytic activities towards ethylene polymerization in the presence of modified methyaluminoxane. The electronic and steric factors attached to the ligand backbone significantly affected both the catalyst activity and the polymer molecular weight. Complex 4b was obtained by the reaction of CrCl₃(thf)₃ with one equivalent of the lithium salts of 4a, which was the most efficient ligand among the tested ones. The effect of polymerization parameters such as cocatalyst concentration, ethylene pressure, reaction temperature, and time on polymerization behavior were investigated in detail. The resulting polymer obtained by 4b display wax-like and possess linear structure, low molecular weight, and unimodal distribution. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 713–721, 2009

Three heteroligated (salicylaldiminato)(β-enaminoketonato)titanium complexes [3-Bu^t-2-OC₆H₃CHN(C₆F₅)][(p-XC₆H₄)NC(Bu^t)CHC(CF₃)O]TiCl₂ (3a: X = F, 3b: X = Cl, 3c: X = Br) were synthesized and investigated as the catalysts for ethylene polymerization and ethylene/norbornene copolymerization. In the presence of modified methylaluminoxane as a cocatalyst, these unsymmetric catalysts exhibited high activities toward ethylene polymerization, similar to their parallel parent catalysts. Furthermore, they also displayed favorable ability to efficiently incorporate norbornene into the polymer chains and produce high molecular weight copolymers under the mild conditions, though the copolymerization of ethylene with norbornene leads to relatively lower activities. The sterically open structure of the β-enaminoketonato ligand is responsible for the high norbornene incorporation. The norbornene concentration in the polymerization medium had a profound influence on the molecular weight distribution of the resulting copolymer. When the norbornene concentration in the feed is higher than 0.4 mol/L, the heteroligated catalysts mediated the living copolymerization of ethylene with norbornene to form narrow molecular weight distribution copolymers (M_w/M_n < 1.20), which suggested that chain termination or transfer reaction could be efficiently suppressed via the addition of norbornene into the reaction medium. Polymer yields, catalytic activity, molecular weight, and norbornene incorporation can be controlled within a wide range by the variation of the reaction parameters such as comonomer content in the feed, reaction time, and temperature. ©2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6072–6082, 2009

A series of (α-diimine)nickel(II) complexes [ArN = C(Nap)C = NAr]NiBr₂ (Nap = 1,8-naphthdiyl, Ar = 2,6-Me₂C₆H₃, 3a; Ar = 2,4,6-Me₃C₆H₂3b; Ar = 2,6-Me₂-4-tBuC₆H₂, 3c; Ar = 2,6-Me₂-4-BrC₆H₂, 3d; Ar = 2,6-Me₂-4-ClC₆H₂, 3e; Ar = 2,6-iPr₂C₆H₃, 3f; Ar = 2,4,6-iPr₃C₆H₂, 3g; Ar = 2,6-iPr-4-BrC₆H₂, 3h) have been synthesized, characterized, and investigated as precatalysts for ethylene polymerization in the presence of modified methylaluminoxane (MMAO). The substituents of α-diimine ligands and their positions located significantly influence catalyst activity and polymer property. It is found that the catalytic activities of the nickel complex/MMAO systems and the microstructure of the polymer obtained are dominated by not only hindering effect of ortho-position substituents but also electronical effect of para-position substituents. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

A series of salicylaldimine-based neutral Ni(II) complexes (3a–j) [ArN = CH(C₆H₄O)]Ni(PPh₃)Ph [3a, Ar = C₆H₅; 3b, Ar = C₆H₄F(o); 3c, Ar = C₆H₄F(m); 3d, Ar = C₆H₄F(p); 3e, Ar = C₆H₃F₂(2,4); 3f, Ar = C₆H₃F₂(2,5); 3g, Ar = C₆H₃F₂(2,6); 3h, Ar = C₆H₃F₂(3,5); 3i, Ar = C₆H₂F₃(3,4,5); 3j, Ar = C₆F₅] have been synthesized in good yield, and the structures of complexes 3a and 3i have been confirmed by X-ray crystallographic analysis. Using modified methylaluminoxane as a cocatalyst, these neutral Ni(II) complexes exhibited high catalytic activities for the vinylic polymerization of norbornene. It was observed that the strong electron-withdrawing effect of the fluorinated salicylaldiminato ligand was able to significantly increase the catalyst activity for vinylic polymerization of norbornenes. In addition, catalyst activity, polymer yield and polymer molecular weight can also be controlled over a wide range by the variation of reaction parameters such as Al:Ni ratio, norbornene:catalyst ratio, monomer concentration, polymerization temperature and time. Copyright © 2008 John Wiley & Sons, Ltd.

A series of novel titanium(IV) complexes combining a phosphine oxide-bridged bisphenolato ligand TiCl₂{2,2′-OP-R₃ (4-R₂-6-R₁-C₆H₂O)₂}(THF) (6a: R₁ = tBu, R₂ = H, R₃ = Ph; 6b: R₁ = Ph, R₂ = H, R₃ = Ph; 6c: R₁ = R₂ = tBu, R₃ = Ph; 6d: R₁ = R₂ = cumyl, R₃ = Ph; 6e: R₁ = tBu, R₂ = H, R₃ = PhF₅) were prepared by the reaction of corresponding bisphenolato ligands with TiCl₄ in THF. X-ray analysis reveals that complex 6a adopts distorted octahedral geometry around the titanium center. These catalysts were performed for ethylene polymerization in the presence of modified methyaluminoxane (MMAO). The effects of reaction parameters on ethylene polymerization behaviors, such as cocatalyst concentration, polymerization temperature, and reaction time were studied in detail. In general, these new complexes exhibited high catalytic activity, good temperature tolerance, and long lifetime for ethylene polymerization. The resulting polymers possess high molecular weight, unimodal distribution, and linear structure. © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7062–7073, 2008

Branched polystyrenes with abundant pendant vinyl functional groups were prepared via radical polymerization of an asymmetric divinyl monomer, which possesses a higher reactive styryl and a lower reactive butenyl. Employing a fast reversible addition fragmentation chain transfer (RAFT) equilibrium, the concentration of active propagation chains remained at a low value and thus crosslinking did not occur until a high level of monomer conversion. The combination of a higher reaction temperature (120 °C) and RAFT agent cumyl dithiobenzoate was demonstrated to be optimal for providing both a more highly branched architecture and a higher polymer yield. The molecular weights (M_ws) increased with monomer conversions because of the controlled radical polymerization characteristic, whereas the M_w distributions broadened showing a result of the gradual increase of the degree of branching. The evolution of branched structure has been confirmed by a triple detection size exclusion chromatography (TRI-SEC) and NMR technique. Furthermore, the double bonds in the side chains were successfully used for chemical modification reactions. ¹H NMR and FTIR measurements reveal that the great mass of pendant vinyl groups were converted to the corresponding objective end-groups. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6023–6034, 2008

Five novel vanadium(III) complexes [PhN = C(R₂)CHC(R₁)O]VCl₂(THF)₂ (4a: R₁ = Ph, R₂ = CF₃; 4b: R₁ = t-Bu, R₂ = CF₃; 4c: R₁ = CF₃, R₂ = CH₃; 4d: R₁ = Ph, R₂ = CH₃; 4e: R₁ = Ph, R₂ = H) have been synthesized and characterized. On activation with Et₂AlCl, all the complexes, in the presence of ethyl trichloroacetate (ETA) as a promoter, are highly active precatalysts for ethylene polymerization, and produce high molecular weight and linear polymers. Catalyst activities more than 16.8 kg PE/mmol_V h bar and weight-average molecular weights higher than 173 kg/mol were observed under mild conditions. The copolymerizations of ethylene and norbornene or 1-hexene with the precatalysts were also explored, which leads to high molecular weight copolymers with high comonomer incorporation. Catalyst activity, comonomer incorporation, and polymer molecular weight as well as polydispersity index can be controlled over a wide range by the variation of precatalyst structure and the reaction parameters such as Al/V molar ratio, comonomer feed concentration, and polymerization temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2038–2048, 2008

A convenient and cost-effective strategy for synthesis of hyperbranched poly(ester-amide)s from commercially available dicarboxylic acids (A₂) and multihydroxyl secondary amine (CB₂) has been developed. By optimizing the conditions of model reactions, the AB₂-type intermediates were formed dominantly during the initial reaction stage. Without any purification, the AB₂ intermediate was subjected to thermal polycondensation in the absence of any catalyst to prepare the aliphatic and semiaromatic hyperbranched poly(ester-amide)s bearing multi-hydroxyl end-groups. The FTIR and ¹H NMR spectra indicated that the polymerization proceeded in the proposed way. The DBs of the resulting polymers were confirmed by a combination of inverse-gated decoupling ¹³C NMR, and DEPT-135 NMR techniques. The DBs of the hyperbranched poly(ester-amide)s were in the range of 0.44–0.73, depending on the structure of the monomers used. The hyperbranched polymers exhibited moderate molecular weights with relatively broad distributions determined by SEC. All the polymers displayed low inherent viscosity (0.11–0.25 dL/g) due to the branched nature. Structural and end-group effects on the thermal properties of the hyperbranched polymers were investigated using DSC. The thermogravimetric analysis revealed that the resulting polymers exhibit reasonable thermal stability. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5077–5092, 2008