The effect of AlR3 on propylene polymerization by rac‐(EBI)Zr(NMe2)2/AlR3/[CPh3][B(C6F5)4] catalyst

Ansa‐zirconocene diamide complex rac‐(EBI)Zr(NMe₂)₂ [rac‐1, EBI = ethylene‐1,2‐bis(1‐indenyl)] reacted with AlR₃ (R = Me, Et, iBu) or Al(iBu₂)H and then with [CPh₃][B(C₆F₅)₄] (2) in toluene in order to perform propylene polymerization by cationic alkylzirconium species, which are in situ generated during polymerization. Through the sequential NMR‐scale reactions of rac‐1 with AlR₃ or Al(iBu₂)H and then with 2, rac‐1 was demonstrated to be transformed to the active alkyzirconium cations via alkylated intermediates of rac‐1. The cationic species generated by using AlMe₃, AlEt₃, and Al(iBu₂)H as alkylating reagents tend to become heterodinuclear complex; however, those by using bulky Al(iBu)₃ become base‐free [rac‐(EBI)Zr(iBu)]⁺ cations. The activity of propylene polymerization by rac‐1/AlR₃/2 catalyst was deeply influenced by various parameters such as the amount and the type of AlR₃, metallocene concentration, [Al]/[2] ratio, and polymerization temperature. Generally the catalytic systems using bulky alkylaluminum like Al(iBu)₃ and Al(iBu)₂H show higher activity but lower stereoregularity than those using less bulky AlMe₃ and AlEt₃. The alkylating reagent Al(iBu)₃ is not a transfer agent as good as AlMe₃ or AlEt₃. The polymerization activities show maximum around [Al]/[2] ratio of 1.0 and increase monotonously with polymerization temperature. The overall activation energy of both rac‐1/Al(iBu)₃/2 and rac‐1/Al(iBu)₂H catalysts is 6.0 kcal/mol. As the polymerization temperature increases, the stereoregularity of the resulting polymer decreases markedly, which is demonstrated by the decrease of [mmmm] pentad value and by the increase of the amount of polymer soluble in low boiling solvent. The physical properties of polymers produced in this study were investigated by using ¹³C‐NMR, differential scanning calorimetry (DSC), viscometry, and gel permeation chromatography (GPC). © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1523–1539, 1999     

Synthesis and Characterization of Crystalline Styrene‐b‐(Ethylene‐co‐Butylene)‐b‐Styrene Triblock Copolymers

By merit of dual catalysis of the cationic rare‐earth complex [(η⁵‐Flu‐CH₂‐Py)Ho(CH₂SiMe₃)₂(THF) (Flu = fluorenyl, Py = pyridyl) for the living polymerizations of butadiene (BD) and styrene (St), the crystalline styrene‐butadiene‐styrene (SBS) triblock copolymers consisting of elastic polybutadiene (PBD) sequences with suitable 1,4 regularity (about 70%) and crystalline syndiotactic polystyrene (sPS, [rrrr] > 99%) sequences were successfully synthesized through sequential addition of St, BD, and St monomers. The catalytic system showed high polymerization activities for St and BD in a controlled manner. The crystalline styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene (SEBS) triblock copolymers were obtained by hydrogenation of the above SBS copolymers. The observation of a strong endothermic peak at 266 °C in their differential scanning calorimetry (DSC) curves confirmed the existence of the sPS blocks in the crystalline SEBS different from the industrial product Kraton SEBS‐1652. Thermal degradation temperature of the crystalline SEBS (418 ± 2 °C) indicated the well thermostability and process window of this polymer. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 55, 1243–1249     

1,4‐Dilithio‐1,1,4,4‐tetraphenylbutane in diethyl ether: An effective initiator for the living anionic polymerization of dienes

The anionic polymerization of butadiene initiated with 1,4‐dilithio‐1,1,4,4‐tetraphenylbutane (LiTPB) in diethyl ether (DEE) gives polybutadiene (PBD) with high 1,2 content (>70%), narrow polydispersities (1.04 < M_w/M_n < 1.20), and predicted molecular weights. In THF, this polymerization does not work very well. After removal of DEE and addition of THF, the PBD dianion is end capped quantitatively by addition of 1,1‐diphenylethylene (DPE) to give the diphenylalkyl end capped PBD dianion. Subsequent addition of methyl methacrylate at low temperatures results in the formation of well‐defined PMMA‐b‐PBD‐b‐PMMA triblock copolymers. The results are accounted for by taking into account the effects of Li ion solvation on the BD initiation and end capping of the PBD anion by DPE. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2198–2206, 2009     

Stereospecific sequential block copolymerizations of styrene and 1,3‐butadiene with a C5Me5TiMe3/B(C6F5)3/Al(oct)3 catalyst

This article reports a new methodology for preparing highly stereoregular styrene (ST)/1,3‐butadiene (BD) block copolymers, composed of syndiotactic polystyrene (syn‐PS) segments chemically bonded with cis‐polybutadiene (cis‐PB) segments, through a stereospecific sequential block copolymerization of ST with BD in the presence of a C₅Me₅TiMe₃/B(C₆F₅)₃/Al(oct)₃ catalyst. The first polymerization step, conducted in toluene at ?25 °C, was attributed to the syndiospecific living polymerization of ST. The second step, conducted at ?40 °C, was attributed to the cis‐specific living polymerization of BD. The livingness of the whole polymerization system was confirmed through a linear increase in the weight‐average molecular weights of the copolymers versus the polymer yields in both steps, whereas the molar mass distributions remained constant. The profound cross reactivity of the styrenic‐end‐group active species with BD toward ST led to the production of syn‐PS‐b‐cis‐PB copolymers with extremely high block efficiencies. Because of the presence of crystallizable syn‐PS segments, this copolymer exhibited high melting temperatures (up to 270 °C), which were remarkably different from those of the corresponding anionic ST–BD copolymers, for which no melting temperatures were observed. Scanning electron microscopy pictures of a binary syn‐PS/cis‐PB blend with or without the addition of the syn‐PS‐b‐cis‐PB copolymers proved that it could be used as an effective compatibilizer for noncompatibilized syn‐PS/cis‐PB binary blends. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1188–1195, 2005     

Copolymerization of propylene and 1,5‐hexadiene with stereospecific metallocene/Al(i‐Bu)3/[Ph3C][B(C6F5)4]

Copolymerizations of propylene (P) with 1,5‐hexadiene (1,5‐HD) were carried out with isospecific rac‐1,2‐ethylenebis(1‐indenyl)Zr(NMe₂)₂ [rac‐(EBI)Zr(NMe₂)₂, 1] and syndiospecific isopropylidene(cyclopentadienyl)(9‐fluorenyl)ZrMe₂ [i‐Pr(Cp)(Flu)ZrMe₂, 2] compounds combined with Al(i‐Bu)₃/[Ph₃C][B(C₆F₅)₄] as a cocatalyst system. Microstructures of poly(propylene‐co‐1,5‐HD) were determined by ¹H NMR, ¹³C NMR, Raman spectroscopies and X‐ray powder diffraction. The isospecific 1/Al(i‐Bu)₃/[Ph₃C][B(C₆F₆)₄] catalyst showed much higher polymerization rate than 2/Al(i‐Bu)₃/[Ph₃C][B(C₆F₆)₄] system, however, the latter system showed higher incorporation of 1,5‐HD (r_P = 8.85, r_1,5‐HD = 0.274) than the former system (r_P = 16.25, r_1,5‐HD = 0.34). The high value of r_P × r_1,5‐HD far above 1 demonstrated that the copolymers obtained by both catalysts are somewhat blocky. The insertion of 1,5‐HD proceeded by enantiomorphic site control; however, the diastereoselectivity of the intramolecular cyclization reaction of 1,2‐inserted 1,5‐HD was independent of the stereospecificity of metallocene compounds, but dependent on the concentration of 1,5‐HD in the feed. The insertion of the monomers by enantiomorphic site control could also be realized by Raman spectroscopy and X‐ray powder diffraction of the polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1590–1598, 2000     

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     

α‐keto‐β‐diimine nickel‐catalyzed olefin polymerization: Effect of ortho‐aryl substituents and preparation of stereoblock copolymers

A series of α‐keto‐β‐diimine nickel complexes (Ar‐N = C(CH₃)‐C(O)‐C(CH₃)=N‐Ar)NiBr₂; Ar = 2,6‐R‐C₆H₃‐, R = Me, Et, iPr, and Ar = 2,4,6‐Me₃‐C₆H₃‐) was prepared. All corresponding ligands are unstable even under an inert atmosphere and in a freezer. Stable copper complex intermediates of ligand synthesis and ethyl substituted nickel complex were isolated and characterized by X‐ray. All nickel complexes were used for the polymerization of ethene, propylene, and hex‐1‐ene to investigate their livingness and the extent of chain‐walking. Low‐temperature propene polymerization with less bulky ortho‐substituents was less isospecific than the one with isopropyl derivative. Propene stereoblock copolymers were prepared by iPr derivative combining the polymerization at low temperature to prepare isotactic polypropylene (PP) block and at a higher temperature, supporting chain‐walking, to obtain amorphous regioirregular PP block. Alternatively, a copolymerization of propene with ethene was used for the preparation of amorphous block. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2440–2449     

Polymerization of MMA catalyzed by different novel mixed ligand lanthanocene{(Cp)(Cl) LnSchiff-base (THF)},(COT) -Ln(methoxyethylindenyl)(THF) /Al (i -Bu)_3 systems

This article deals that the rare earth metal complexes along with Al(i'-Bu),can catalyze the polymerization of methyl-methacrylate (MMA) into high molecular weight poly(MMA) along with narrow molecular weight distributions (MWD).A typical example was mentioned in the case of {Cp(Cl) Sm-Schiff-base(THF)} which expresses maximum (conv.% = 55.46 and Mn=354×103) efficiency along with narrow MWD (Mw/Mn<2) at 60℃.The resulting polymer was partially syndiotactic (>60%).The effect of the catalyst,temperature,catalyst/MMA molar ratio,catalyst/Al( i-Bu)3 molar ratio on the polymerization of MMA at 60℃ were also investigated.     

Ethylene polymerization over supported catalysts [2,6‐bis(imino)pyridyl iron dichloride/magnesium dichloride] with AlR3 as an activator

Data on ethylene polymerization over supported LFeCl₂/MgCl₂ catalysts {L = 2,6‐bis[1‐(2,6‐dimethylphenylimino)ethyl]pyridyl} containing AlR₃ (R = Me, Et, i‐Bu, or n‐Oct) as an activator are presented. These catalysts are highly active (100–300 kg of polyethylene/g of Fe h bar of C₂H₄) and stable in ethylene polymerization at 70–80 °C. Data on the effects of the iron content, AlR₃ type, Al(i‐Bu)₃ concentration, and hydrogen presence on the catalyst activity are presented. The molecular structure of polyethylene produced with these catalysts (including the molecular masses, molecular mass distribution, branching, and number of C?C bonds) has been studied; data on the effects of AlR₃ and hydrogen on the molecular structure are presented. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2128–2133, 2005     

MAO‐free polymerization of propylene by rac‐ Me2Si(1‐C5H2‐2‐Me‐4‐tBu)2Zr(NMe2)2 compound

Ansa‐zirconocene diamide complex rac‐Me₂Si(CMB)₂Zr(NMe₂)₂ (rac‐1, CMB = 1‐C₅H₂‐2‐Me‐4‐^tBu) reacts with AlR₃ (R = Me, Et, i‐Bu) and then with [CPh₃]⁺[B(C₆F₅)₄]⁻ (2) in toluene in order to in situ generate cationic alkylzirconium species. In the sequential NMR‐scale reactions of rac‐1 with various amount of AlMe₃ and 2, rac‐1 transforms first to rac‐Me₂Si(CMB)₂Zr(Me)(NMe₂) (rac‐3) and rac‐Me₂Si(CMB)₂ZrMe₂ (rac‐4) by the reaction with AlMe₃, and then to [rac‐Me₂Si(CMB)₂ZrMe]⁺ (5⁺) cation by the reaction of the resulting mixtures with 2. The activities of propylene polymerizations by rac‐1/Al(i‐Bu)₃/2 system are dependent on the type and concentration of AlR₃, resulting in the order of activity: rac‐1/Al(i‐Bu)₃/2 > rac‐1/AlEt₃/2 > rac‐1/MAO ≫ rac‐1/AlMe₃/2 system. The bulkier isobutyl substituents make inactive catalytic species sterically unfavorable and give rise to more separated ion pairs so that the monomers can easily access to the active sites. The dependence of the maximum rate (R_{p, max}) on polymerization temperature (T_p) obtained by rac‐1/Al(i‐Bu)₃/2 system follows Arrhenius relation, and the overall activation energy corresponds to 0.34 kcal/mol. The molecular weight (MW) of the resulting isotactic polypropylene (iPP) is not sensitive to Al(i‐Bu)₃ concentration. The analysis of regiochemical errors of iPP shows that the chain transfer to Al(i‐Bu)₃ is a minor chain termination. The 1,3‐addition of propylene monomer is the main source of regiochemical sequence and the [mr] sequence is negligible, as a result the meso pentad ([mmmm]) values of iPPs are very high ([mmmm] > 94%). These results can explain the fact that rac‐1/Al(i‐Bu)₃/2 system keeps high activity over a wide range of [Al(i‐Bu)₃]/[Zr] ratio between 32 and 3,260. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1071–1082, 1999     

Synthesis and structural characterization of syndiotactic trans‐1,2 and cis‐1,2 polyhexadienes

The (E) isomer in mixtures of (E) and (Z) 1,3‐hexadiene was polymerized with the system CoCl₂(PⁱPrPh₂)₂‐MAO, a highly active and stereospecific catalyst for the preparation of 1,2 syndiotactic polybutadiene. A new crystalline polymer with a melting point of 109 °C was obtained. The polymer was characterized by IR, NMR (¹³C, ¹H in solution and ¹³C in the solid‐state), X‐ray diffraction, DSC, GPC and it was found to have a trans‐1,2 syndiotactic structure with a 5.18 ± 0.04 Å fiber periodicity. Since only the (E) isomer was polymerized, at the end of the reaction we were able to separate the (Z) isomer, which was ultimately polymerized with CpTiCl₃‐MAO at low temperature, obtaining a low molecular weight, stereoregular polymer that, characterized by IR and NMR methods, was found to exhibit a cis‐1,2 syndiotactic structure, never reported before. Molecular mechanics calculations were carried out on the trans‐1,2 syndiotactic polymer and structural models consistent with the X‐ray diffraction data are proposed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5339–5353, 2007     

Higher α‐olefin polymerizations catalyzed by rac‐Me2Si(1‐C5H2‐2‐CH3‐4‐tBu)2Zr(NMe2)2/Al(iBu)3/[Ph3C][B(C6F5)4]

Polymerizations of higher α‐olefins, 1‐pentene, 1‐hexene, 1‐octene, and 1‐decene were carried out at 30 °C in toluene by using highly isospecific rac‐Me₂Si(1‐C₅H₂‐2‐CH₃‐4‐^t Bu)₂Zr(NMe₂)₂ (rac‐1) compound in the presence of Al(iBu)₃/[CPh₃][B(C₆F₅)₄] as a cocatalyst formulation. Both the bulkiness of monomer and the lateral size of polymer influenced the activity of polymerization. The larger lateral of polymer chain opens the π‐ligand of active site wide and favors the insertion of monomer, while the large size of monomer inserts itself into polymer chain more difficultly due to the steric hindrance. Highly isotactic poly(α‐olefin)s of high molecular weight (MW) were produced. The MW decreased from polypropylene to poly(1‐hexene), and then increased from poly(1‐hexene) to poly(1‐decene). The isotacticity (as [mm] triad) of the polymer decreased with the increased lateral size in the order: poly(1‐pentene) > poly(1‐hexene) > poly(1‐octene) > poly(1‐decene). The similar dependence of the lateral size on the melting point of polymer was recorded by differential scanning calorimetry (DSC). ¹H NMR analysis showed that vinylidene group resulting from β‐H elimination and saturated methyl groups resulting from chain transfer to cocatalyst are the main end groups of polymer chain. The vinylidene and internal double bonds are also identified by Raman spectroscopy. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1687–1697, 2000     

Kinetics of propylene polymerization initiated by rac‐Me2Si(1‐C5H2‐2‐Me‐4‐tBu)2Zr(NME2)2/MAO catalyst

The kinetics of propylene polymerization initiated by ansa‐metallocene diamide compound rac‐Me₂Si(CMB)₂Zr(NMe₂)₂ (rac‐1, CMB = 1‐C₅H₂‐2‐Me‐4‐^tBu)/methylaluminoxane (MAO) catalyst were investigated. The formation of cationic active species has been studied by the sequential NMR‐scale reactions of rac‐1 with MAO. The rac‐1 is first transformed to rac‐Me₂Si(CMB)₂ZrMe₂ (rac‐2) through the alkylation mainly by free AlMe₃ contained in MAO. The methylzirconium cations are then formed by the reaction of rac‐2 and MAO. Small amount of MAO ([Al]/[Zr] = 40) is enough to completely activate rac‐1 to afford methylzirconium cations that can polymerize propylene. In the lab‐scale polymerizations carried out at 30°C in toluene, the rate of polymerization (R_p) shows maximum at [Al]/[Zr] = 6,250. The R_p increases as the polymerization temperature (T_p) increases in the range of T_p between 10 and 70°C and as the catalyst concentration increases in the range between 21.9 and 109.6 μM. The activation energies evaluated by simple kinetic scheme are 4.7 kcal/mol during the acceleration period of polymerization and 12.2 kcal/mol for an overall reaction. The introduction of additional free AlMe₃ before activating rac‐1 with MAO during polymerization deeply influences the polymerization behavior. The iPPs obtained at various conditions are characterized by high melting point (approximately 155°C), high stereoregularity (almost 100% [mmmm] pentad), low molecular weight (MW), and narrow molecular weight distribution (below 2.0). The fractionation results by various solvents show that iPPs produced at T_p below 30°C are compositionally homogeneous, but those obtained at T_p above 40°C are separated into many fractions. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 737–750, 1999     

Polymerization of n-Octylallene with Rare Earth Catalyst Composed of Ln(P204)3/Al(i-Bu)3

Polymerization of n‐octylallene was successfully carried out using a conventional binary rare earth catalytic system composed of rare earth tris(2‐ethylhexylphosphonate) (Ln(P₂₀₄)₃) and tri‐isobutyl aluminum (Al(i‐Bu)₃) for the first time. The effects of catalyst, solvent, reaction time and temperature on the polymerization of n‐octylallene were studied. The resulting poly(n‐octylallene) has weight‐average molecular weight of 11000, molecular weight distribution of 1.4 and 96% yield under the moderate reaction conditions: [Al]/[Y] =50 (molar ratio), [n‐octylallene]/[Y] =100 (molar ratio), polymerized at 80°C for 20 h in bulk. The poly(n‐octylallene) obtained consisted of 1,2‐ and 2,3‐polymerized units, and was characterized by FT‐IR, ¹H NMR and GPC. Further investigation shows that the polymerization of n‐octylallene has some living polymerization characteristics, preparing the polymer with controlled molecular weight and narrower molecular weight distribution.     

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

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

Synthesis of poly(3‐hexylthiophene)‐block‐poly(ethylene)‐block‐poly(3‐hexylthiophene) via a combination of ring‐opening olefin metathesis polymerization and grignard metathesis polymerization

Novel rod–coil–rod ABA triblock copolymers, poly(3‐hexylthiophene)‐block‐poly(ethylene)‐block‐poly(3‐hexylthiophene) (P3HT‐b‐PE‐b‐P3HT) were synthesized by using a combination of a Ru‐catalyzed ring‐opening metathesis polymerization of 1,4‐cyclooctadiene in the presence of a suitable chain transfer agent (CTA) and a Ni‐catalyzed Grignard metathesis polymerization of 5‐chloromagnesio‐2‐bromo‐3‐hexylthiophene followed by hydrogenation. Using this methodology, the molecular weights of the poly(butadiene) (PBD) or the P3HT blocks were controlled by adjusting the initial monomer/CTA or the initial monomer/macroinitiator ratio, respectively. In addition, the triblock structure was confirmed by selective oxidative degradation of the PBD block found in the intermediate P3HT‐b‐PBD‐b‐P3HT copolymer produced in the aforementioned method, followed by analysis of the degradation products. Thermal analysis and atomic force microscopy of P3HT‐b‐PE‐b‐P3HT revealed that the material underwent phase separation in the solid state, a feature which may prove useful for improving charge mobilities within electronic devices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3810–3817     

Synthesis of azide end‐functionalized isotactic polypropylene building block and renewed modular synthesis of diblock copolymers of isotactic polypropylene and poly(ε‐caprolactone)

This article details a synthesis of azide end‐functionalized isotactic polypropylene (i‐PP), a unique polymeric building block that can engage in Huisgen's 1,3‐dipolar cycloaddition of azide and alkyne (click reaction) to construct well‐defined i‐PP‐based polymer architecture. Controlled, consecutive chain transfer reaction to 1,2‐bis(4‐vinylphenyl)ethane and hydrogen in metallocene‐mediated propylene polymerization catalyzed by rac‐Me₂Si(2‐Me‐4‐Ph‐Ind)₂ZrCl₂/MAO resulted in styryl‐terminated i‐PP (i‐PP‐t‐St) of controlled molecular weight. Following a regioselective hydrochlorination reaction, the terminal styryl groups were quantatively transformed to 1‐chloroethylbenzene groups, which was further reacted with NaN₃ to give i‐PP terminated with an azide group (i‐PP‐t‐N₃). Structural monitoring of the polymers through the whole transformation process using ¹H NMR and FTIR as well as GPC and DSC reveals a clean and clear formation of i‐PP‐t‐N₃ (M_n in between 10,000 and 40,000 g/mol). This clickable i‐PP building block was applied to a renewed, modular synthesis of amphiphilic i‐PP‐b‐PCL (poly(ε‐caprolactone)) diblock copolymers. Composition‐diversified, structure‐well defined diblock copolymers were obtained in high yields, confirming both the high end group selectivity as well as high reactivity of azide the clickable moiety in the i‐PP building block and the effectiveness of azide‐alkyne click reaction in constructing new i‐PP architecture. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Molecular structure determination of Ni(II) diimine complex and DMA analysis of Ni(II) diimine‐based polyethenes

Dynamic mechanical thermoanalysis showed that polyethene, prepared under suitable polymerization conditions with the Brookhart‐type catalyst dibromo‐N,N′‐1,2‐acenaphthylenediylidenebis[2,6‐bis(1‐methylethyl)benzeneamine]Ni(II)/methylaluminoxane (MAO), behaved like an elastomer, even though no comonomer was added. A structural characterization showed that the polymers contained methyl to hexyl branches and some longer branches. The effect of the polymerization conditions on branching was investigated through variations in the pressure and temperature of the polymerization. Depending on the degree and type of branching, polyethene was either quite amorphous or highly crystalline with a high melting temperature. The solid‐state structure of the catalyst dibromo‐N,N′‐1,2‐acenaphthylenediylidenebis[2,6‐bis(1‐methylethyl)benzeneamine]Ni(II) consisted of two centrosymmetrically related monomeric moieties, where Ni atoms were bridged by two bromide ligands. The Ni atom was five‐coordinated, with a square pyramidal coordination polyhedron. The sixth coordination site of the octahedral geometry was effectively blocked by the isopropyl groups of the 2,6‐C₆H₃(i‐Pr) substituents of the diimine ligand. In solution in the presence of MAO, the longer bridging Ni? Br bonds broke, and the complex dissociated to a monomeric species. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1426–1434, 2001     

Copolymerization of ethylene and cyclopentene with bis(β‐enaminoketonato) titanium complexes

The copolymerizations of ethylene and cyclopentene with bis(β‐enaminoketonato) titanium complexes {[(Ph)NC(R₂)CHC(R₁)O]₂TiCl₂; R₁ = CF₃ and R₂ = CH₃ for 1a , R₁ = Ph and R₂ = CF₃ for 1b ; and R₁ = t‐Bu and R₂ = CF₃ for 1c } activated with modified methylaluminoxane (MMAO) as a cocatalyst were investigated. High‐molecular‐weight copolymers with cis‐1,2‐cyclopentene units were obtained. The catalyst activity, cyclopentene incorporation, polymer molecular weight, and polydispersity could be controlled over a wide range through the variation of the catalyst structure and reaction parameters, such as the Al/Ti molar ratio, cyclopentene feed concentration, and polymerization reaction temperature. The complex 1b /MMAO catalyst system exhibited the characteristics of a quasi‐living ethylene polymerization and an ethylene–cyclopentene copolymerization and allowed the synthesis of polyethylene‐block‐poly(ethylene‐co‐cyclopentene) diblock copolymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1681–1689, 2005     

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