Stereospecific and molecular weight‐controlled polymerization of 1,3‐butadiene with Co(acac)3‐MAO catalyst

The polymerization of butadiene (Bd) with Co(acac)₃ in combination with methylaluminoxane (MAO) was investigated. The polymerization of Bd with Co(acac)₃‐MAO catalysts proceeded to give cis‐1,4 polymers (94 – 97%) bearing high molecular weights (40 × 10⁴) with relatively narrow molecular weight distributions (M_w's/M_n's). The molecular weight of the polymers increased linearly with the polymer yield, and the line passed through an original point. The polydispersities of the polymers kept almost constant during reaction time. This indicates that the microstructure and molecular weight of the polymers can be controlled in the polymerization of Bd with the Co(acac)₃‐MAO catalyst. The effects of reaction temperature, Bd concentration, and the MAO/Co molar ratio on the cis‐1,4 microstructure and high molecular weight polymer in the polymerization of Bd with Co(acac)₃‐MAO catalyst were observed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2793–2798, 2001     

Polymerization of 2‐pentene with Ni(II) α‐diimine complex/M‐MAO catalyst and structure of the polymer

Polymerization of 2‐pentene with [ArN?C(An)C(An)·NAr)NiBr₂ (Ar?2,6‐iPr₂C₆H₃)] ( 1‐Ni) /M‐MAO catalyst was investigated. A reactivity between trans‐2‐pentene and cis‐2‐pentene on the polymerization was quite different, and trans‐2‐pentene polymerized with 1‐Ni /M‐MAO catalyst to give a high molecular weight polymer. On the other hand, the polymerization of cis‐2‐butene with 1‐Ni /M‐MAO catalyst did not give any polymeric products. In the polymerization of mixture of trans‐ and cis‐2‐pentene with 1‐Ni /M‐MAO catalyst, the M_n of the polymer increased with an increase of the polymer yields. However, the relationship between polymer yield and the M_n of the polymer did not give a strict straight line, and the M_w/M_n also increased with increasing polymer yield. This suggests that side reactions were induced during the polymerization. The structures of the polymer obtained from the polymerization of 2‐ pentene with 1‐Ni /M‐MAO catalyst consists of ? CH₂? CH₂? CH(CH₂CH₃)? , ? CH₂? CH₂? CH₂? CH(CH₃)? , ? CH₂? CH(CH₂CH₂CH₃)? , and methylene sequence ? (CH₂)_n? (n ≥ 5) units, which is related to the chain walking mechanism. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2858–2863, 2008     

Polymerization of isoprene with η5‐C5H4(tert‐Bu)TiCl3/MAO catalyst

cis‐Selective polymerizations of isoprene with the catalysts composed of η⁵‐C₅H₄(R)TiCl₃ (1; R?H, 2 ; tert‐Bu) and methylaluminoxane were investigated. Both catalysts showed remarkable catalytic activities for the polymerization of isoprene. The polymerization activities were strongly affected by the substituent introduced on cyclopentadienyl ring. Introduction of bulky tert‐butyl group was found to be effective for enhancement of polymerization activity, but the cis‐content of polyisoprene prepared by the 2 /MAO catalyst was lower than that by 1 /MAO catalyst. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1841–1844, 2004     

Preparation of high cis‐1,4 polyisoprene with narrow molecular weight distribution via coordinative chain transfer polymerization

High cis‐1,4 polyisoprene with narrow molecular weight distribution has been prepared via coordinative chain transfer polymerization (CCTP) using a homogeneous rare earth catalyst composed of neodymium versatate (Nd(vers)₃), dimethyldichlorosilane (Me₂SiCl₂), and diisobutylaluminum hydride (Al(i‐Bu)₂H) which has strong chain transfer affinity is used as both cocatalyst and chain transfer agent (CTA). Differentiating from the typical chain shuttling polymerization where dual‐catalysts/CSA system has been used, one catalyst/CTA system is used in this work, and the growing chain swapping between the identical active sites leads to the formation of high cis‐1,4 polyisoprene with narrowly distributed molecular weight. Sequential polymerization proves that irreversible chain termination reactions are negligible. Much smaller molecular weight of polymer obtained than that of stoichiometrically calculated illuminates that, differentiating from the typical living polymerization, several polymer chains can be produced by one neodymium atom. The effectiveness of Al(i‐Bu)₂H as a CTA is further testified by much broad molecular weight distribution of polymer when triisobutylaluminum (Al(i‐Bu)₃), a much weaker chain transfer agent, is used as cocatalyst instead of Al(i‐Bu)₂H. Finally, CCTP polymerization mechanism is validated by continuously decreased M_w/M_n value of polymer when increasing concentration of Al(i‐Bu)₂H extra added in the Nd(ver)₃/Me₂SiCl₂/Al(i‐Bu)₃ catalyst system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Control of molecular weight in polymerization of vinyl chloride with Cp*Ti(OPh)3/MAO catalyst

Polymerization of vinyl chloride (VC) with titanium complexes containing Ti‐OPh bond in combination with methylaluminoxane (MAO) catalysts was investigated. Among the titanium complexes examined, Cp*Ti(OPh)₃/MAO catalyst (Cp*; pentamethylcyclopentadienyl, Ph; C₆H₅) gave the highest activity for the polymerization of VC, but the polymerization rate was slow. From the kinetic study on the polymerization of VC with Cp*Ti(OPh)₃/MAO catalyst, the relationship between the M_n of the polymer and the polymer yields gave a straight line, and the line passed through the origin. The M_w/M_n values of the polymer gradually decrease as a function of polymer yields, but the M_w/M_n values were somewhat broad. This may be explained by a slow initiation in the polymerization of VC with Cp*Ti(OPh)₃/MAO catalyst. The results obtained in this study demonstrate that the molecular weight control of the polymers is possible in the polymerization of VC with the Cp*Ti(OPh)₃/MAO catalyst. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3872–3876, 2007     

Factors affecting product distributions in ethylene/styrene copolymerization by (aryloxo)(cyclopentadienyl)titanium complexes‐MAO catalyst systems

Ethylene/styrene copolymerizations using Cp′TiCl₂(O‐2,6‐ⁱPr₂C₆H₃) [Cp′ = Cp* (C₅Me₅, 1 ), 1,2,4‐Me₃C₅H₂ ( 2 ), tert‐BuC₅H₄ ( 3 )]‐MAO catalyst systems were explored under various conditions. Complexes 2 and 3 exhibited both high catalytic activities (activity: 504–6810 kg‐polymer/mol‐Ti h) and efficient styrene incorporations at 25, 40°C (ethylene 6 atm), affording relatively high molecular weight poly (ethylene‐co‐styrene)s with unimodal molecular weight distributions as well as with uniform styrene distributions (M_w = 6.12–13.6 × 10⁴, M_w/M_n = 1.50–1.71, styrene 31.7–51.9 mol %). By‐productions of syndiotactic polystyrene (SPS) were observed, when the copolymerizations by 1 – 3 ‐MAO catalyst systems were performed at 55, 70 °C (ethylene 6 atm, SPS 9.0–68.9 wt %); the ratios of the copolymer/SPS were affected by the polymerization temperature, the [styrene]/[ethylene] feed molar ratios in the reaction mixture, and by both the cyclopentadienyl fragment (Cp′) and anionic ancillary donor ligand (L) in Cp′TiCl₂(L) (L = Cl, O‐2,6‐ⁱPr₂C₆H₃ or N=C^tBu₂) employed. Co‐presence of the catalytically‐active species for both the copolymerization and the homopolymerization was thus suggested even in the presence of ethylene; the ratios were influenced by various factors (catalyst precursors, temperature, styrene/ethylene feed molar ratio, etc.). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4162–4174, 2008     

Effects of tris(pentafluorophenyl)borane on the activation of a metal alkyl‐free Ni‐based catalyst in the polymerization of 1,3‐butadiene

The activation of a metal alkyl‐free Ni‐based catalyst with B(C₆F₅)₃ was investigated in the polymerization of 1,3‐butadiene. A catalyst of bis(1,5‐cyclooctadiene)nickel (Ni(COD)₂)/B(C₆F₅)₃ was found to have high catalytic activity and 1,4‐cis stereoregularity. The catalyst was also found to provide polybutadiene having a molecular weight (M_w) of up to 117,000, even in the absence of AlR₃ and MAO. Variations in the mol ratio of B(C₆F₅)₃ to Ni affected catalytic activity, 1,4‐cis stereoregularity, and the M_w of polybutadiene, while the molecular weight distribution (MWD) of polybutadiene showed little correlation with the mol ratio of B(C₆F₅)₃ to Ni. The use of other borane compounds such as B(C₆H₅)₃, BEt₃, and BF₃ etherate in place of B(C₆F₅)₃ clearly showed the two main functions of B(C₆F₅)₃ in the present catalyst. The high Lewis acidity of B(C₆F₅)₃ enabled it to activate catalytic complexes, thus inducing the polymerization. The steric bulkiness of B(C₆F₅)₃ suppressed chain transfer reactions, contributing to the production of polybutadiene with a high M_w. Kinetic studies showed that the catalyst had an induction period, possibly due to the time needed for the formation of catalytic complexes starting from Ni(COD)₂. A plot of ?ln (1?X), where X is the fractional conversion, as a function of time resulted in a linear relationship, showing that the present catalyst system followed first‐order kinetics with respect to monomer concentration. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1164–1173, 2004     

Microwave‐improved polymerization of ϵ‐caprolactone initiated by carboxylic acids

The ring‐opening polymerization of ε‐caprolactone (ε‐CL), initiated by carboxylic acids such as benzoic acid and chlorinated acetic acids under microwave irradiation, was investigated; with this method, no metal catalyst was necessary. The product was characterized as poly(ε‐caprolactone) (PCL) by ¹H NMR spectroscopy, Fourier transform infrared spectroscopy, ultraviolet spectroscopy, and gel permeation chromatography. The polymerization was significantly improved under microwave irradiation. The weight‐average molecular weight (M_w) of PCL reached 44,800 g/mol, with a polydispersity index [weight‐average molecular weight/number‐average molecular weight (M_w/M_n)] of 1.6, when a mixture of ε‐CL and benzoic acid (25/1 molar ratio) was irradiated at 680 W for 240 min, whereas PCL with M_w = 12,100 and M_w/M_n = 4.2 was obtained from the same mixture by a conventional heating method at 210 °C for 240 min. A degradation of the resultant PCL was observed during microwave polymerization with chlorinated acetic acids as initiators, and this induced a decrease in M_w of PCL. However, the degradation was hindered by benzoic acid at low concentrations. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 13–21, 2003     

Isoprene polymerization with indolide‐imine supported rare‐earth metal alkyl and amidinate complexes

Reaction of 7‐{(N‐2,6‐R)iminomethyl)}indole ( HL¹ , R = dimethylphenyl; HL² , R = diisopropylphenyl) and rare‐earth metal tris(alkyl)s, Ln(CH₂SiMe₃)₃(THF)₂, generated new rare‐earth metal bis(alkyl) complexes LLn(CH₂SiMe₃)₂(THF) [L = L¹: Ln = Lu ( 1a ), Sc ( 1b ); L = L²: Ln = Lu ( 3a ), Sc ( 3b )] and mono(alkyl) complexes L²₂Lu(CH₂SiMe₃) ( 4a ). Treatment of alkyl complexes 1a and 4a with N,N′‐diisopropylcarbodiimide afforded the corresponding amidinates L¹Lu{iPr₂NC(CH₂SiMe₃)NiPr₂}₂ ( 2a ) and L²₂Lu{iPr₂NC(CH₂SiMe₃)NiPr₂} ( 5a ), respectively. These new rare‐earth metal alkyls and amidinates except 4a in combination with aluminum alkyls and borate generated efficient homogeneous catalysts for the polymerization of isoprene, providing high cis‐1,4 selectivity and high molar mass polyisoprene with narrow molar mass distribution (M_n = 2.65 × 10⁵, M_w/M_n = 1.07, cis‐1,4 98.2%, −60 °C). The environmental hindrance around central metals arising from the bulkiness of the ligands, the Lewis‐acidity of rare‐earth metal ions, the types of aluminum tris(alkyl)s and borate, and polymerization temperature influenced significantly on both the catalytic activity and the regioselectivity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5251–5262, 2008     

Designed organo‐layered silicates as nanoreactors for 1,3‐butadiene stereospecific polymerization toward rubber nanocomposites synthesis

Organo‐modified layered silicates were synthesized and used as inorganic carriers for CoCl₂(P^tBu₂Me)₂‐MAO catalyst in the polymerization of 1,3‐butadiene, yielding cis‐1,4‐enriched polybutadiene. The organoclays were prepared by: (i) intercalation of (ar‐vinyl‐benzyl)trimethyl ammonium chloride salt through an ion exchange reaction, and (ii) the edge‐surface grafting by trimethylchlorosilane. The ammonium modifier acts as “spacer” increasing the layer d‐spacing and as “filler” favoring the silylation of the edge‐surface clay hydroxyls. The grafted silane prevents the MAO cocatalyst from reacting with the edge‐OHs, by forcing it to react within the interlayer clay region. MAO lead to methylation of the cobalt complex and carbanion abstraction to give a cobalt‐methyl cation that is stabilized by the MAO anion. The nanoconfined cationic alkylated species insert the butadiene on the Co‐Me bond affording the growth of the polymer chains within the clay layers. The growing of the macromolecular chains fills the interlayer silicate region giving an intercalated polybutadiene rubber nanocomposite. The role of the silicate organo modification on the heterogeneous catalyst structural features, the polymerization behavior and the nanocomposite structures are discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Titanium complexes of dialkanolamine ligands as initiators for living ring‐opening polymerization of ε‐caprolactone

The titanium complexes with one ( 1a , 1b , 1c ) and two ( 2a , 2b ) dialkanolamine ligands were used as initiators in the ring‐opening polymerization (ROP) of ε‐caprolactone. Titanocanes 1a and 1b initiated living ROP of ε‐caprolactone affording polymers whose number‐average molecular weights (M_n) increased in direct proportion to monomer conversion (M_n ≤ 30,000 g mol^?1) in agreement with calculated values, and were inversely proportional to initiator concentration, while the molecular weight distribution stayed narrow throughout the polymerization (M_w/M_n ≤ 1.2 up to 80% monomer conversion). ¹H‐NMR and MALDI‐TOF‐MS studies of the obtained poly(ε‐caprolactone)s revealed the presence of an isopropoxy group originated from the initiator at the polymer termini, indicating that the polymerization takes place exclusively at the Ti–OⁱPr bond of the catalyst. The higher molecular weight polymers (M_n ≤ 70,000 g mol^?1) with reasonable MWD (M_w/M_n ≤ 1.6) were synthesized by living ROP of ε‐caprolactone using spirobititanocanes ( 2a , 2b ) and titanocane 1c as initiators. The latter catalysts, according MALDI‐TOF‐MS data, afford poly(ε‐caprolactone)s with almost equal content of α,ω‐dihydroxyl‐ and α‐hydroxyl‐ω(carboxylic acid)‐terminated chains arising due to monomer insertion into “Ti–O” bond of dialkanolamine ligand and from initiation via traces of water, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1230–1240, 2010     

The ligand effect in Ti‐mediated living radical styrene polymerizations initiated by epoxide radical ring opening. 1. Alkoxide and bisketonate Ti complexes

Bisketonate and alkoxide Ti(III) complexes derived from Zn reduction of Ti(IV) precursors were evaluated as catalysts for the living radical polymerization (LRP) of styrene initiated by Ti‐catalyzed epoxide radical ring opening and mediated by reversible termination with Ti(III). No polymerization occurred with tris(2,2,6, 6‐tetramethyl‐3,5‐heptanedionato)titanium (III), whereas dichlorobis(2,2,6,6‐tetramethyl‐3,5‐heptanedionato)titanium (IV) affords only a free radical polymerization. Preliminary living features were displayed by (ⁱPrO)₂TiCl₂. Investigations of the effect of epoxide/Ti/Zn ratios, temperature, and nature of the epoxide demonstrated that (ⁱPrO)₃TiCl provides a linear dependence of M_n on conversion over a wide range of conditions with an optimum for [Sty]/[epoxide group]/[Ti]/[Zn] = 50/1/2/4 at 90 °C. However, the polydispersity could not be reduced below 1.4–1.5, with an initiator efficiency of 0.15. These results were rationalized in terms of a combination of decreased Ti oxophilicity and ligand exchange. The lowered oxophilicity decreases the initiation rate and broadens M_w/M_n. The fast alkoxide exchange promotes a weak dependence of the polymerization on reaction conditions and generates macromolecular Ti species with reduced ability to mediate LRP. Thus, while monofunctional epoxides provide homogeneous polymerizations and narrower M_w/M_n, difunctional initiators may lead to gel formation at high conversion. Nonetheless, all polymerizations were light gray to colorless and afforded white polymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6028–6038, 2005     

Ring‐opening metathesis polymerization of cis‐cyanocyclooct‐4‐ene: Search for active catalysts,variation of monomer to catalyst ratios and monomer concentrations

The ring‐opening metathesis polymerization (ROMP) of cis‐cyanocyclooct‐4‐ene initiated by ruthenium‐based catalysts of the first, second, and third generation was studied. For the polymerization with the second generation Grubbs catalyst [RuCl₂(?CHPh)(H₂IMes)(PCy₃)] (H₂IMes = N,N′‐bis(mesityl)‐4,5‐dihydroimidazol‐2‐ylidene), the critical monomer concentration at which polymerization occurs was determined, and variation of monomer to catalyst ratios was performed. For this catalyst, ROMP of cis‐cyanocyclooct‐4‐ene did not show the features of a living polymerization as M_n did not linearly increase with increasing monomer conversion. As a consequence of slow initiation rates and intramolecular polymer degradation, molar masses passed through a maximum during the course of the polymerization. With third generation ruthenium catalysts (which contain 3‐bromo or 2‐methylpyridine ligands), polymerization proceeded rapidly, and degradation reactions could not be observed. Contrary to ruthenium‐based catalysts of the second and third generation, a catalyst of the first generation was not able to polymerize cis‐cyanocyclooct‐4‐ene. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Atactic polymerization of propylene catalyzed by mono(η5-cyclopentadienyl)titanium tribenzyloxide combined with methylaluminoxane

Propylene has been polymerized with mono(η⁵-cyclopentadienyl)titanium tribenzyloxide activated with methylaluminoxane (MAO). It was found that the content of residual trimethylaluminium (TMA) in MAO has a determinative effect on the polymerization. An excess of TMA in the catalyst system reduces the Ti species to inactive lower valent states. The catalyst system gives medium molecular-weight atactic polypropylene (M_v = 2–7 × 10⁴) with narrow molecular weight distribution (M_w/M_n = 1.4–1.8). The polymer has a stereoirregular structure described by Bernoullian statistics. Statistical analysis of the regiotriad distribution of the polypropylene chains indicates a regioblock microstructure. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2051–2057, 1998     

1,2 Enriched polymerization of isoprene by cobalt complex carrying aminophosphory fused (PN3) ligand

Metal-catalyzed selective isoprene polymerization has been a major entry toward cis-1,4, trans-1,4, and 3,4 isomers of polyisoprene, however, 1,2 selective polymerization of isoprene has not yet been achieved due to the steric problem. In this work, difluoro cobalt complexes carrying aminophosphory (-HN-P(=O) ^tBu₂-) fused pyrazol-pyridine ligand has been prepared and characterized. In combination with Mg^n-Bu₂, the formed catalyst unprecedentedly converts isoprene to polyisoprene with 1,2 enchainment up to 50 mol% in a molecular weight controlled polymerization mode. The resultant polymers are fully characterized by NMR, IR, DSC, and GPC. The 1,2 incorporation of polyisoprene is weakly dependent on feeding of Mg^n-Bu₂ and reaction temperature. The weak affinity between Mg²⁺ and allylic terminal of propagating chain is possible for the unique 1,2 irregular insertion and non-irreversible chain transfer and termination reactions throughout the chain propagation. The ability of current catalyst demonstrates a big advantage for application in the development of 1,2 selective polymerization of isoprene, and a potential for access to a new family of polyisoprene. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2286–2293     

Polymerization of (E)‐1,3‐Pentadiene and (E)‐2‐methyl‐1,3‐pentadiene with neodymium catalysts: Examination of the factors that affect the stereoselectivity

(E)‐1,3‐Pentadiene (EP) and (E)‐2‐methyl‐1,3‐pentadiene (2MP) were polymerized to cis‐1,4 polymers with homogeneous and heterogeneous neodymium catalysts to examine the influence of the physical state of the catalyst on the polymerization stereoselectivity. Data on the polymerization of (E)‐1,3‐hexadiene (EH) are also reported. EP and EH gave cis‐1,4 isotactic polymers both with the homogeneous and with the heterogeneous system, whereas 2MP gave an isotactic cis‐1,4 polymer with the heterogeneous catalyst and a syndiotactic cis‐1,4 polymer, never reported earlier, with the homogeneous one. For comparison, the results obtained with the soluble CpTiCl₃‐based catalyst (Cp = cyclopentadienyl), which gives cis‐1,4 isotactic poly(2MP), are examined. A tentative interpretation is given for the mechanism of the formation of the stereoregular polymers obtained and a complete NMR characterization of the cis‐1,4‐syndiotactic poly(2MP) is reported. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3227–3232     

AGET ATRP of water‐soluble PEGMA: Fast living radical polymerization mediated by iron catalyst

In this work, living radical polymerizations of a water‐soluble monomer poly(ethylene glycol) monomethyl ether methacylate (PEGMA) in bulk with low‐toxic iron catalyst system, including iron chloride hexahydrate and triphenylphosphine, were carried out successfully. Effect of reaction temperature and catalyst concentration on the polymerization of PEGMA was investigated. The polymerization kinetics showed the features of “living”/controlled radical polymerization. For example, M_n,GPC values of the resultant polymers increased linearly with monomer conversion. A faster polymerization of PEGMA could be obtained in the presence of a reducing agent Fe(0) wire or ascorbic acid. In the case of Fe(0) wire as the reducing agent, a monomer conversion of 80% was obtained in 80 min of reaction time at 90 °C, yielding a water‐soluble poly(PEGMA) with M_n = 65,500 g mol^?1 and M_w/M_n = 1.39. The features of “living”/controlled radical polymerization of PEGMA were verified by analysis of chain‐end and chain‐extension experiments. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Propylene polymerizations with a binary metallocene system—Chain shuttling caused by trimethylaluminium between active catalyst centers

Propylene was polymerized at varying trimethylaluminium (TMA) concentration with a homogeneous binary metallocene catalyst system activated by methylaluminoxane (MAO) in an attempt to better understand interactions between active catalyst sites and to clarify the role of the TMA as a chain shuttling agent. TMA‐free polymerization conditions were obtained by chemical treatment of MAO solution with 2,6‐di‐tert‐butyl‐4‐methylphenol (BHT). A binary catalyst system consisting of catalyst precursors diphenylmethyl(cyclopentadienyl)(9‐fluorenyl)zirconium dichloride ( 1 ) producing high M_w syndiotactic polypropylene and rac‐dimethylsilylbis(4‐tert‐butyl‐2‐methyl‐cyclopentadienyl)zirconium dichloride ( 2 ) producing low M_w isotactic polypropylene was investigated. At the studied polymerization conditions, chain shuttling between the active catalysts caused by TMA was confirmed. The chain shuttling reactions caused changes in catalyst activity, molecular weights, melting behavior, and polymer microstructure. We propose that TMA is capable to transfer a growing polymer chain from catalyst 2 to catalyst 1 , and a stereoblock copolymer is formed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1364–1376, 2007     

Polymerization of 1,3‐dienes and styrene catalyzed by cationic allyl Ni(II) complexes

Polymerizations of 1,3‐dienes using in situ generated catalyst [(2‐methallyl)Ni][B(Ar_F)₄], 6 , (Ar_F = 3,5‐bis(trifluoromethyl)phenyl) as well as [(2‐methallyl)Ni(mes)][B(Ar_F)₄], 14 , (mes = mesitylene) are reported. Highly sensitive complex 6 polymerizes butadiene (BD) at –30 °C to yield polybutadiene with a M_n of ca. 10 K and 94% cis‐1,4‐enchainment while less reactive isoprene (IP) was polymerized at 23 °C to yield polyisoprene with M_n ca. 7 K. Complex 6 was also shown to polymerize a functionalized diene, 2,3‐bis(4‐trifluoroethoxy‐4‐oxobutyl)‐1,3‐BD, to polymer with M_n = 113 K. The stable and readily isolated arene complex 14 initiates BD and IP polymerizations at somewhat higher temperatures relative to 6 and delivers polymers with higher molecular weights. Complex [(allyl)Ni(mes)][B(Ar_F)₄], 13 , catalyzes polymerization of styrene to yield polystyrene with high conversion, M_n's = ca. 6 K and MWD = 2. The π‐benzyl complex [(η³‐1‐methylbenzyl)Ni(mes)] [B(Ar_F)₄], 19 , was detected as an intermediate following chain transfer by in situ NMR studies. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1901–1912, 2010     

Synthesis of well‐defined polyacrylonitrile by ICAR ATRP with low concentrations of catalyst

Acrylonitrile (AN) was polymerized by initiators for continuous activator regeneration (ICAR) atom transfer radical polymerization (ATRP). The effect of the ligand, tris(2‐pyridylmethyl)amine (TPMA) and N,N,N',N'‐tetrakis(2‐pyridylmethyl)ethylenediamine (TPEN), in the Cu‐based catalyst, the amount of catalyst, several alkyl halide initiators, targeted degree of polymerization, and amount of azobisisobutyronitrile (AIBN) added were studied. It was determined that the best conditions utilized 50 ppm of CuBr₂/TPMA as the catalyst and 2‐bromopropionitrile (BPN) as the initiator. This combination resulted in 46% conversion in 10 h and polyacrylonitrile (PAN) with the narrowest molecular weight distribution (M_w/M_n = 1.11–1.21). Excellent control was maintained after lowering the catalyst loading to 10 ppm, with 56% conversion in 10 h, experimental molecular weight closely matching the theoretical value, and low dispersity (M_w/M_n < 1.30). Catalyst loadings as low as 1 ppm still provided well‐controlled polymerizations of AN by ICAR ATRP, with 65% conversion in 10 h and PAN with relatively low dispersity (M_w/M_n = 1.41). High chain end functionality (CEF) was confirmed via ¹H NMR analysis, for short PAN chains, and via clean chain extensions with n‐butyl acrylate (BA). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1961–1968