Norbornene/n‐Butyl methacrylate copolymerization over α‐Diimine nickel and palladium catalysts supported on multiwalled carbon nanotubes

The covalently immobilized multiwalled carbon nanotubes (MWNTs) supported three‐dimensional geometry α‐diimine nickel, palladium catalysts are prepared by corresponding α‐diimine nickel, palladium complexes and activated MWNTs. The molecular structures of the catalysts have been confirmed by X‐ray single‐crystal analyses, NMR and XPS, as well as elemental analysis. Compared with nickel, palladium catalysts without modification and physical mixing of nickel, palladium catalysts with MWNTs, the MWNTs supported nickel, palladium catalysts show improved activity and productivity in norbornene homopolymerization and copolymerization with polar monomer. The morphology of the resulting polymers obtained from MWNTs‐supported nickel(II) complex reveals that the MWNTs are dispersed uniformly in polymer and wrapped by polymers to squeeze out of spherical particles, leading to the enhanced processability and mechanical properties. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3213–3220     

Olefin Polymerization Catalyzed by Double‐Decker Dipalladium Complexes: Low Branched Poly(α‐Olefin)s by Selective Insertion of the Monomer Molecule

Dipalladium complexes of a cyclic bis(diimine) ligand with a double‐decker structure catalyze polymerization of ethylene and α‐olefins and copolymerization of ethylene with 1‐hexene. The polymerization of 1‐hexene yields a polymer that is mainly composed of the hexamethylene unit formed by 2,1‐insertion of the monomer into the palladium–carbon bond, followed by chain‐walking (6,1‐insertion). The polymerization of 4‐methyl‐1‐pentene proceeds by 2,1‐insertion with a selectivity of 92–97 %, and affords the polymer with methyl and 2‐methylhexyl branches. 2,1‐Insertion occurs selectively in all of the polymerization reactions of α‐olefins catalyzed by the dipalladium complexes. Ethylene polymerization with the catalyst at 100 °C lasts over 24 h, whereas the monopalladium–diimine catalyst loses its activity within 8 h at 60 °C. Polyethylene obtained by the dipalladium catalyst is less‐branched and has a higher molecular weight compared to that of the monopalladium catalyst under the same conditions. Copolymerization of ethylene with 1‐hexene affords solid products with melting points and molecular weights that vary depending on the polymerization time, suggesting formation of a block and/or gradient copolymer.     

Poly(1‐hexene) with long methylene sequences and controlled branches obtained by a thermostable α‐diimine nickel catalyst with bulky camphyl backbone

1‐Hexene polymerizations catalyzed by α‐diimine nickel complexes after activation with modified methylaluminoxane were performed at various reaction temperatures. Effects of catalyst structure and polymerization temperature on activity and polymer microstructure were evaluated in detail. Bulky catalyst 1b with camphyl backbone exhibited good control ability and greatly enhanced thermal stability to be capable of polymerizing 1‐hexene at 80°C. The poly(1‐hexene)s with long methylene sequences and dominate branches (methyl and butyl) were synthesized using catalyst 1b . Differential scanning calorimetry analysis further confirmed that long polymethylene block (? (CH₂)_n? , n > 20) was formed in the poly(1‐hexene)s with melting point of 64°C obtained by catalyst 1b on the basis of initial branched model polyethylene. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A Second‐Coordination‐Sphere Strategy to Modulate Nickel‐ and Palladium‐Catalyzed Olefin Polymerization and Copolymerization

Transition‐metal‐catalyzed copolymerization reactions of olefins with polar‐functionalized comonomers are highly important and also highly challenging. A second‐coordination‐sphere strategy was developed to address some of the difficulties encountered in these copolymerization reactions. A series of α‐diimine ligands bearing nitrogen‐containing second coordination spheres were prepared and characterized. The properties of the corresponding nickel and palladium catalysts in ethylene polymerizations and copolymerizations were investigated. In the nickel system, significant reduction in polymer branching density was observed, while lower polymer branching densities, as well as a wider range of polar monomer substrates, were achieved in the palladium system. Control experiments and computational results reveal the critical role of the metal−nitrogen interaction in these polymerization and copolymerization reactions.     

Living and stereoselective polymerization of rac‐lactide by bimetallic aluminum Schiff‐Base complexes

A series of bimetallic aluminum Schiff‐base complexes have been prepared and characterized. The complexes used as catalysts were applied in the lactide polymerization to test their activities and stereoselectivities. All polymerizations are living, as evidenced by the narrow polydispersities and the good fit between calculated and found number‐average molecular weights of the isolated polymers. Isotactic enriched polylactide was obtained by using these complexes. Kinetic studies indicated that the polymerizations are both first‐ordered with respect to lactide monomer and catalyst. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1344–1352     

Copolymerization of ethylene with 1‐hexene promoted by novel multi‐chelated non‐metallocene complexes with imine bridged imidazole ligand

A series of novel bridged multi‐chelated non‐metallocene catalysts is synthesized by the treatment of N,N‐imidazole, N,N‐dimethylimidazole, and N,N‐benzimidazole with n‐BuLi, 2,6‐dimethylaniline, and MCl₄ (M = Ti, Zr) in THF. These catalysts are used for copolymerization of ethylene with 1‐hexene after activated by methylaluminoxane (MAO). The effects of polymerization temperature, Al/M molar ratio, and pressure of monomer on ethylene copolymerization behaviors are investigated in detail. These results reveal that these catalysts are favorable for copolymerization of ethylene with 1‐hexene featured high catalytic activity and high comonomer incorporation. The copolymer is characterized by ¹³C NMR, WAXD, GPC, and DSC. The results confirm that the obtained copolymer features broad molecular weight distribution (MWD) about 33–35 and high 1‐hexene incorporation up to 9.2 mol %, melting temperature of the copolymer depends on the content of 1‐hexene incorporation within the copolymer chain and 1‐hexene unit in the copolymer chain isolates by ethylene units. The homopolymer of ethylene has broader MWD with 42–46. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 417–424, 2010     

Visible light‐induced RAFT polymerization of methacrylates with benzaldehyde derivatives as organophotoredox catalysts

The benzaldehyde derivatives, such as 2,4‐dimethoxy benzaldehyde (PC1) and p‐anisaldehyde (PC2), were successfully used as photoredox catalysts (PCs) in combination with typical RAFT agent 4‐cyano‐4‐(phenylcarbonothioylthio)pentanoic acid (CTP) for the controlled photoinduced electron transfer RAFT polymerization (PET‐RAFT) of methyl methacrylate (MMA) and benzyl methacrylate (BnMA) at room temperature. The kinetics of the polymerizations showed first order with respect to monomer conversions. Besides, the average number molecular weights (M_n) of the produced polymers increased linearly with the monomer conversions and kept relatively narrow polydispersity (PDI = M_w/M_n). For example, the M_n of PMMA increased from about 3400 to 17,300 g mol⁻¹ with the increasing in monomer conversion from 11% to 85%, and the PDI maintained around 1.36. The living features of polymerizations with the PC1 and PC2 as catalysts have also been further supported by chain extension and synthesis of PMMA‐b‐PBnMA diblock copolymer. As a result, the simplicity and efficiency of benzaldehyde derivatives catalyzed PET‐RAFT polymerization have been demonstrated under mild conditions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 229–236     

Synthesis and cleavage of core‐labile poly(alkyl methacrylate) star polymers

Core‐cleavable star polymers were synthesized by the coupling of living anionic poly(alkyl methacrylate) arms with either dicumyl alcohol dimethacrylate (DCDMA) or 2,5‐dimethyl‐2,5‐hexanediol dimethacrylate (DHDMA). This synthetic methodology led to the formation of star polymers that exhibited high molecular weights and relatively narrow molecular weight distributions. The labile tertiary alkyl esters in the DCDMA and DHDMA star polymer cores were readily hydrolyzed under acidic conditions. High‐molecular‐weight star polymer cleavage led to well‐defined arm polymers with lower molecular weights. Hydrolysis was confirmed via ¹H NMR spectroscopy and gel permeation chromatography. Thermogravimetric analysis (TGA) of the star polymers demonstrated that the DCDMA and DHDMA star polymer cores also thermally degraded in the absence of acid catalysts at 185 and 220 °C, respectively, and the core‐cleavage temperatures were independent of the arm polymer composition. The difference in the core‐degradation temperatures was attributed to the increased reactivity of the DCDMA‐derived cores. TGA/mass spectrometry detected the evolution of the diene byproduct of the core degradation and confirmed the proposed degradation mechanism. The DCDMA monomer exhibited a higher degradation rate than DHDMA under identical reaction conditions because of the additional resonance stabilization of the liberated byproduct, which made it a more responsive cleavable coupling monomer than DHDMA. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3083–3093, 2003     

Thiol‐epoxy polymerization via an AB monomer: Synthetic access to high molecular weight poly(β‐hydroxythio‐ether)s

A synthetic route is developed for the preparation of an AB‐type of monomer carrying an epoxy and a thiol group. Base‐catalyzed thiol‐epoxy polymerization of this monomer gave rise to poly(β‐hydroxythio‐ether)s. A systematic variation in the reaction conditions suggested that tetrabutyl ammonium fluoride, lithium hydroxide, and 1,8‐diazabicycloundecene (DBU) were good polymerization catalysts. Triethylamine, in contrast, required higher temperatures and excess amounts to yield polymers. THF and water could be used as polymerization mediums. However, the best results were obtained in bulk conditions. This required the use of a mechanical stirrer due to the high viscosity of the polymerization mixture. The polymers obtained from the AB monomer route exhibited significantly higher molecular weights (M_w = 47,700, M_n = 23,200 g/mol) than the materials prepared from an AA/BB type of the monomer system (M_w = 10,000, M_n = 5400 g/mol). The prepared reactive polymers could be transformed into a fluorescent or a cationic structure through postpolymerization modification of the reactive hydroxyl sites present along the polymer backbone. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2040–2046     

Single and binary catalyst systems based on nickel and palladium in polymerization of ethylene

The catalyst (N,N‐bis(2,6‐dibenzhydryl‐4‐ethoxyphenyl)butane‐2,3‐diimine)nickel dibromide, a late transition metal catalyst, was prepared and used in ethylene polymerization. The effects of reaction parameters such as polymerization temperature, co‐catalyst to catalyst molar ratio and monomer pressure on the polymerization were investigated. The α‐diimine nickel‐based catalyst was demonstrated to be thermally robust at a temperature as high as 90 °C. The highest activity of the catalyst (494 kg polyethylene (mol cat)^?1 h^?1) was obtained at [Al]/[Ni] = 600:1, temperature of 90 °C and pressure of 5 bar. In addition, the performance of a binary catalyst using nickel‐ and palladium‐based complexes was compared with that of the corresponding individual catalytic systems in ethylene polymerization. In a study of the catalyst systems, the average molecular weight and molecular weight distribution for the binary polymerization were between those for the individual catalytic polymerizations; however, the binary catalyst activity was lower than that of the two individual ones. The obtained polyethylenes had high molecular weights in the region of 10⁵ g mol^?1. Gel permeation chromatography analysis showed a narrow molecular weight distribution of 1.44 for the nickel‐based catalyst and 1.61 for the binary catalyst system. The branching density of the polyethylenes generated using the binary catalytic system (30 branches/1000 C) was lower than that generated using the nickel‐based catalyst (51/1000 C). X‐ray diffraction study of the polymer chains showed higher crystallinity with lower branching of the polymer obtained. Also Fourier transform infrared spectra confirmed that all obtained polymers were low‐density polyethylene.     

Seleno‐containing poly(vinyl acetate) prepared by diselenocarbonates‐mediated controlled free radical polymerizations

The living free radical polymerizations of vinyl acetate (VAc) were successfully achieved in the presence of a novel organic selenium compound (diselenocarbonates), with 2,2′‐azobisisobutyronitrile (AIBN) as the initiator. The living characteristics of the VAc polymerization were confirmed by the linear first‐order kinetic plots and linear increase of molecular weights (M_n) of the polymers with monomer conversions, while keeping the relatively low molecular weight distributions. In addition, the end of the polymers contains selenium element which may be useful in biotechnological and biomedical applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3159–3165     

Polar,functionalized diene‐based materials. V. Free‐radical polymerization of 2‐[(N‐benzyl‐n‐methylamino)methyl]‐1,3‐butadiene and copolymerization with styrene

2‐[(N‐Benzyl‐N‐methylamino)methyl]‐1,3‐butadiene (BMAMBD), the first asymmetric tertiary amino‐containing diene‐based monomer, was synthesized by sulfone chemistry and a nickel‐catalyzed Grignard coupling reaction in high purity and good yield. The bulk and solution free‐radical polymerizations of this monomer were studied. Traditional bulk free‐radical polymerization kinetics were observed, giving polymers with 〈M_n〉 values of 21 × 10³ to 48 × 10³ g/mol (where M_n is the number‐average molecular weight) and polydispersity indices near 1.5. In solution polymerization, polymers with higher molecular weights were obtained in cyclohexane than in tetrahydrofuran (THF) because of the higher chain transfer to the solvent. The chain‐transfer constants calculated for cyclohexane and THF were 1.97 × 10^?3 and 5.77 × 10^?3, respectively. To further tailor polymer properties, we also completed copolymerization studies with styrene. Kinetic studies showed that BMAMBD incorporated into the polymer chain at a faster rate than styrene. With the Mayo–Lewis equation, the monomer reactivity ratios of BMAMBD and styrene at 75 °C were determined to be 2.6 ± 0.3 and 0.28 ± 0.02, respectively. Altering the composition of BMAMBD in the copolymer from 17 to 93% caused the glass‐transition temperature of the resulting copolymer to decrease from 64 to ?7 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3227–3238, 2001     

Application of ketenes to well‐defined polyester synthesis. II. Synthesis of reactive polyester by living anionic polymerization of (4‐halophenyl)ethylketene

Novel ketenes, (4‐chlorophenyl)ethylketene and (4‐bromophenyl)ethylketene, were synthesized by dehydrochlorination of 2‐(4‐halophenyl)butanoyl chlorides, and their anionic polymerizations by lithium (4‐methoxyphenoxide) in tetrahydrofuran at ?20 °C were carried out to afford the corresponding polyesters with narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight < 1.3) quantitatively. Polymerizations with various feed ratios afforded the corresponding polyesters with predictable molecular weights and narrow molecular weight distributions. Kinetic studies of the polymerizations at ?78 °C revealed that the polymerization rates were apparently larger than that of ethylphenylketene, which is considered to be responsible for the enhanced electrophilicities of the monomers via the introduction of electron‐negative halogen atoms. Monomer conversion agreed with the first‐order kinetic equation. These results strongly support the living mechanism of this polymerization. The obtained polyesters were modified by a palladium‐catalyzed coupling reaction of the side‐chain 4‐halophenyl group with 4‐methoxyphenylboronic acid, demonstrating their potential as reactive polymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2093–2102, 2001     

N‐Bromosuccinimide as a thermal iniferter for radical polymerization

N‐Bromosuccinimide (NBS) was used as a thermal iniferter for the initiation of the bulk polymerizations of methyl methacrylate, methyl acrylate, and styrene. The polymerizations showed the characteristics of a living polymerization: both the yields and the molecular weights of the resultant polymers increased linearly as the reaction time increased. The molecular weight distributions of the polymers were 1.42–1.95 under the studied conditions. The resultant polymers could be used as macroiniferters to reinitiate the polymerization of the second monomer. The copolymers poly(methyl methacrylate)‐b‐polystyrene and polystyrene‐b‐poly(methyl methacrylate) were obtained and characterized. End‐group analysis of the resultant poly(methyl methacrylate), poly(methyl acrylate), and polystyrene confirmed that NBS behaved as a thermal iniferter. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2567–2573, 2005     

Regiocontrolled synthesis of poly(3‐alkylthiophene)s by Grignard metathesis

Poly(3‐octadecylthiophene)s (P3OTs) were prepared via Grignard metathesis polymerization of 2,5‐dibromo‐3‐octadecylthiophene in the presence of palladium and nickel catalysts. The effect of catalyst structure and reaction temperature on the regioregularity of P3OTs was investigated. Nickel catalysts provided P3OTs with higher regioregularity, while palladium catalysts gave lower regioregularity. Surprisingly, the regioregularity of P3OTs increased when the polymerization was conducted at higher temperature. The catalyst and temperature dependence of the regioregularity is consistent with two competing mechanisms. Polymerizations at higher temperature with nickel catalysts occur primarily via chain‐growth reactions, while polymerizations at lower temperature with palladium catalysts have competing step‐growth and chain growth reactions. P3OTs with higher regioregularity have longer wavelength visible absorptions, while P3OTs with lower regioregularity have shorter wavelength absorptions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5538–5547, 2004     

Stereospecific polymerization of 1‐hexene catalyzed by ansa‐metallocene/methylaluminoxane systems under high pressures

Stereospecific polymerization of 1‐hexene under high pressures (up to 1,000 MPa = ca. 10,000 atm) using metallocene/methylaluminoxane (MAO) catalysts was investigated. Several C₂‐symmetric ansa‐metallocenes, their meso‐isomers, and two C_s‐symmetric ansa‐metallocenes were employed as catalyst precursors. In the course of this study, novel C₂‐symmetric germylene‐bridged ansa‐metallocenes, (rac‐[Me₂Ge(η⁵‐C₅H‐2,3,5‐Me₃)₂MCl₂] (M = Zr, rac‐4a; M = Hf, rac‐4b), have been prepared. High pressures induced enhancement of the catalytic activity and the molecular weight of the polymers in most of the catalysts. The maximum of both the catalytic activity and the molecular weight of the polymers was mostly observed at 100–500 MPa in each catalyst, although the enhanced ratio was smaller than that observed for nonbridged metallocenes. Isospecificity of the C₂‐symmetric ansa‐metallocene catalysts was essentially maintained even under high pressure. Highly isotactic polyhexene ([mmmm] = 91.6%) with very high molecular weight (M_w = 2,360,000) was achieved by rac‐4b under 250 MPa. High pressures slightly decreased syndiotacticity when the C_s‐symmetric ansa‐metallocene, isopropylidene(1‐η⁵‐cyclopentadienyl)(9‐η⁵‐fluorenyl)zirconium dichloride 5, was employed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 283–292, 1999     

α‐Diimine nickel catalyst for copolymerization of hexene and acrylate monomers activated by different cocatalysts

Bulk homopolymerization and copolymerization of 1‐hexene (H) with polar monomers including butyl acrylate (B) and methyl methacrylate (M) in the presence of 1,4‐bis (2,6‐diisopropylphenyl) acenaphthene diimine nickel (II) dibromide catalyst were investigated. Two cocatalysts, including diethyl aluminium chloride (DEAC) and ethyl aluminium sesqui chloride (EASC), were used to activate the catalyst at ambient temperature. In both the homopolymerization and copolymerization of 1‐hexene with polar monomers, the catalyst activity resulted from EASC as cocatalyst was higher than that resulted from DEAC. ¹HNMR analysis was used in order to determine incorporation level of polar monomers and branching density of the synthesized polymers. A highest incorporation level of 13.3% mol was obtained using monomer B in the presence of the cocatalyst EASC. In addition, the influence of polar monomers on molecular weight and molecular weight distribution (PDI) was studied for both the homo‐ and co‐polymerizations of 1‐hexene in the presence of various cocatalysts. A higher molecular weight and narrower PDI were obtained by using the DEAC cocatalyst compared to the EASC cocatalyst. Glass transition temperature (Tg) and melting point (Tm) of the synthesized polymers were found to be dependent on the cocatalyst type and comonomer incorporation level. The addition of dichloromethane solvent into reaction medium showed a positive effect on comonomer incorporation which could not be seen in bulk polymerization. However, the presence of dichloromethane led to decrease the catalyst activity and molecular weight of the polymers.     

Homopolymerizations and random copolymerizations of olefins with amino‐substituted cyclopentadienylchromium complexes

1‐(2‐N,N‐Dimethylaminoethyl)‐2,3,4,5‐tetramethylcyclopentadienyl‐chromium dichloride ( 1 ), (2‐N,N‐dimethylaminoethyl)cyclopentadienylchromium dichloride ( 6 ), and (2‐N,N‐dimethylaminoethyl)indenylchromium dichloride ( 7 ) in the presence of modified methylaluminoxane exhibit high catalytic activities for the polymerization of ethylene with random copolymerizations of ethylene with propylene, ethylene with 1‐hexene, and propylene with 1‐hexene. These initiators conduct polymerizations to give high molecular weight polymers with low polydispersities. However, the stereoregularities are very poor in these reactions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2759–2771, 2002     

Preparation and characterization of optically active polystyrene via a chiral nitroxide‐mediated polymerization

2,2,6,6‐Tetramethyl‐4‐[d‐(+)‐10‐camphorsulfonyl]‐1‐piperidinyloxy was synthesized and used as a chiral nitroxide for the bulk polymerizations of styrene initiated with benzoyl peroxide (BPO), tetraethylthiuram disulfide (TETD), and thermal initiation. The results showed that the polymerizations proceeded in a controlled/living way; that is, the kinetics presented approximately first‐order plots, and the number‐average molecular weights of the polymers with narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight) increased with the monomer conversion linearly. The molecular weight distributions in the case of thermal initiation were narrower than those in the case of BPO and TETD, whereas the polymerization rate with BPO or TETD as an initiator was obviously faster than that with thermal initiation. In addition, successful chain‐extension reactions were carried out, and the structures of the obtained polymers were characterized by gel permeation chromatography and ¹H NMR. The specific rotations of the polymers were also measured by polarimetric analysis. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1522–1528, 2006     

Semi‐Crystalline Polar Polyethylene: Ester‐Functionalized Linear Polyolefins Enabled by a Functional‐Group‐Tolerant,Cationic Nickel Catalyst

A dibenzobarrelene‐bridged, α‐diimine Ni^II catalyst (rac‐ 3 ) was synthesized and shown to have exceptional behavior for the polymerization of ethylene. The catalyst afforded high molecular weight polyethylenes with narrow dispersities and degrees of branching much lower than those made by related α‐diimine nickel catalysts. Catalyst rac‐ 3 demonstrated living behavior at room temperature, produced linear polyethylene (T_m=135 °C) at ?20 °C, and, most importantly, was able to copolymerize ethylene with the biorenewable polar monomer methyl 10‐undecenoate to yield highly linear ester‐functionalized polyethylene.