Propylene Polymerization Behavior of Fluorinated Bis(phenoxy‐imine) Ti Complexes with an MgCl2‐Based Compound (MgCl2‐Supported Ti‐Based Catalysts)

Summary: Fluorinated bis(phenoxy‐imine)Ti complexes 1 – 3 combined with MgCl₂/i‐Bu_nAl(OR)_3−n (MgCl₂‐supported catalysts) were able to polymerize propylene in a living fashion at room temperature to provide slightly to highly syndiotactic poly(propylenes) (PPs) with extremely narrow distributions of molecular weight. These represent the first examples of MAO‐ and borate‐free group 4 metal‐based living catalysts. The supported complexes 2 and 3 formed PPs with higher syndiotacticity and T_m's than the corresponding homogeneous MAO‐activation systems (e.g., 3 : rr 97%, T_m 155 °C; MAO activation: rr 93%, T_m 152 °C). The measured T_m of 155 °C represents the highest known T_m for syndiotactic PPs synthesized at room temperature.

Polymerization of propylene to poly(propylene) with supported Ti‐based catalysts.     

Semi‐Batch Polymerisations of Ethylene with Metallocene Catalysts in the Presence of Hydrogen, 3. Correlation Between Hydrogen Sensitivity and Molecular Parameters

Semi‐batch ethylene polymerisations have been carried out with heterogenised Cp₂ZrCl₂/MAO, Ind₂ZrCl₂/MAO, Cp(Ind)ZrCl₂/MAO and Cp(Flu)ZrCl₂/MAO (MAO, methylaluminoxane) catalysts where hydrogen was added as the chain‐transfer agent. Modelling of molecular weight distributions of the polymer formed gave estimates of the relative rate constant for the chain transfer to hydrogen and the rate constant for propagation, k/k_p. Values of 0.7(2), 22(7), 13(3) and 35(4) were obtained for the Cp₂, Ind₂, (Cp,Ind) and (Cp,Flu) catalysts, respectively. The observed order of reactivity towards hydrogen has been correlated with chemical shifts from ⁹¹Zr NMR and with the atomic charges of zirconium from DFT calculations for a series of metallocene complexes. The efficiency of hydrogen as a chain‐transfer agent is larger the more electron deficient the zirconium atom in the catalyst is.     

Synthesis and Characterization of Hyperbranched Polyethylenes Made with Nickel‐α‐Diimine Catalysts

The polymerization of ethylene in the presence of 1,4‐bis(2,6‐diisopropylphenyl)acenaphthenediiminenickel(II) dichloride ( 1 ) and methylaluminoxane (MAO) gives hyperbranched polyethylene (HBPE) in appropriate reaction conditions. The system 1 /MAO is active in solvents like toluene or hexane at temperatures as high as 80 °C and ethylene pressures ranging from 1 to 15 atm. The polyethylenes obtained show high molecular weights (up to 467 kg · mol^?1) and more than 218 branches per 1 000 backbone carbon atoms, qualifying these materials as hyperbranched. Dynamic‐mechanical thermal analysis (DMTA) of these materials shows high β‐transitions, directly related to the branch content of these polyethylenes.

DMTA analysis of polyethylenes obtained with 1 /MAO at 0, 30, and 50 °C (corresponding to entries 1, 2 and 3).     

Kinetic Peculiarities of Ethylene Polymerization over Homogeneous Bis(imino)pyridine Fe(II) Catalysts with Different Activators

Summary: Method of polymerization inhibition by radioactive carbon monoxide (¹⁴CO) has been used to determine the number of active centers (C_P) and propagation rate constant (k_P) for ethylene polymerization with homogeneous complex 2,6‐(2,6‐(Me)₂C₆H₃NCMe)₂C₅H₃NFeCl₂ (LFeCl₂), activated with methylalumoxane (MAO) or Al(i‐Bu)₃. With both activators the rate profile of polymerization was unstable: high activity [0.8 × 10³–1.5 × 10³ kg PE per (mol_Fe · h · atm) at 35 °C] of the initial period sharply decreases (sevenfold in 10 min). In the beginning of polymerization with the catalysts LFeCl₂/MAO and LFeCl₂/Al(i‐Bu)₃, the C_P values were found to be 8 and 41% of total Fe‐complex content in catalysts, respectively, and decreased 1.5–2‐fold in 9 min. As polymerization proceeds, the k_P value for LFeCl₂/MAO system decreases from 5 × 10⁴ to 1.5 × 10⁴ L · (mol · s)⁻¹ LFeCl₂/MAO, and for LFeCl₂/Al(i‐Bu)₃ system from 2.6 × 10⁴ to 0.82 × 10⁴ L · (mol · s)⁻¹. Data on the effect of polymerization time on polyethylene molar mass distribution are presented. Basing on the obtained results it was suggested that highly reactive, but unstable centers, dominating at short polymerization times, produce low‐molar‐mass polyethylene, while polyethylene with higher molar mass is produced by less active (low k_P) and more stable centers.

Data showing change in molar mass distribution of polyethylene with polymerization time.     

Ethylene Polymerization with Sila‐Bridged Dinuclear Zirconocene Catalysts

A series of sila‐bridged dinuclear zirconocenes [E(C₅H₄)₂][Cp′ZrCl₂]₂ (Cp′=C₅H₅, E = Me₂Si ( 1 ), Me₂SiSiMe₂ ( 2 ), Me₂SiOSiMe₂ ( 3 ), Me₂SiOSiMe₂OSiMe₂ ( 4 ); Cp′=C₅HMe₄, E = Me₂SiOSiMe₂ ( 5 ), Me₂SiOSiMe₂OSiMe₂ ( 6 )) have been synthesized. These complexes have been studied as catalysts for ethylene polymerization in the presence of MAO. Polymerization results indicated that the polymerization activity of the zirconocenes increased as the bridging ligand became longer for the same type of bridging ligands. Complex 4 , holding trisiloxane bridging, exhibited greater activity than the mononuclear zirconocene [Cp₂ZrCl₂]. All the siloxane‐bridged dinuclear zirconocenes showed the highest activity at higher temperature (60 or 70°C) in contrast to the corresponding siloxane‐bridged dinuclear cyclopentadienyl and indenyl zirconocenes which showed a maximum activity at 40°C. The molecular weight of polyethylene with 4 was very high at low temperature (13.43×10⁵ g·mol^–1 at 20°C) but decreased significantly with increasing temperature. The molecular weight distributions obtained for polyethylene were similar with the mononuclear metallocene catalysts at low temperatures and slightly broad at higher temperatures. The tetramethylcyclopentadienyl complexes 5 and 6 showed lower polymerization activities than the corresponding cyclopentadienyl complexes 3 and 4 as a result of steric effects. The relationship between structures and catalytic properties of catalysts has been discussed.     

Novel SiO2‐Supported Chromium Oxide/Chromocene Dual Site Catalysts for Synthesis of Bimodal UHMWPE/HDPE in Reactor Alloys

Polyethylene (PE) with bimodal molecular weight distribution (MWD) has drawn attention from both academia and industry. Bimodal PE combines great processability with outstanding mechanical properties. The single‐reactor technology process through a dual site catalyst system is an optimal strategy considering the economic effect and the manufacturing technique. To satisfy the demand of the dual site catalyst system for producing bimodal PE, novel SiO₂‐supported chromium oxide/chromocene dual site catalysts for ethylene polymerization are successfully synthesized and systematically investigated. The novel catalysts are prepared by using the residual hydroxyl groups on the surface of SiO₂‐supported chromium oxide (CrO_x) Phillips catalyst to introduce chromocene. It is found that the novel dual site catalysts combine the advantages of chromocene catalyst (S‐9 catalyst) and Phillips CrO_x/SiO₂ catalyst. The activities of the dual site catalysts are doubled at least compared to the S‐9 catalyst due to the high activity of the CrO_x active center. The products of the dual site catalysts show significantly high molecular weight (MW) with bimodal MWD through ultrahigh molecular weight polyethylene/high‐density polyethylene in reactor alloys. The dual site catalysts show great hydrogen response according to the hydrogen experiment results, which lead to the easy control of MW.     

Synthesis of AB2 3‐ and AB4 5‐Miktoarm Star Copolymers Initiated from Dendritic Tri‐ and Penta‐Functional Initiators by Combination of Ring‐Opening Polymerization of ε‐Caprolactone and Nitroxide‐Mediated Radical Polymerization of Styrene

Summary: Well‐defined AB₂ 3‐ and AB₄ 5‐miktoarm star copolymers were prepared by combination of ring‐opening polymerization (ROP) and nitroxide‐mediated radical polymerization (NMRP) using dendritic tri‐ and penta‐functional initiators. Initially, two kinds of dendritic initiators having one benzylic OH and two or four TEMPO‐based alkoxyamine moieties were prepared. Using them, ROP of ε‐caprolactone was carried out at room temperature to give poly(ε‐caprolactone)s carrying two or four alkoxyamine moieties. NMRP of styrene from the poly(ε‐caprolactone)s was carried out at 120 °C to give AB₂ 3‐ and AB₄ 5‐miktoarm star copolymers, which were analyzed by ¹H NMR and SEC. The increased linearly with conversion and the were in the range 1.10–1.37, showing that well‐defined AB₂ 3‐ and AB₄ 5‐miktoarm star copolymers were formed.

Well‐defined AB₂ 3‐ and AB₄ 5‐miktoarm star copolymers were prepared by combination of ring‐opening polymerization (ROP) and nitroxide‐mediated radical polymerization (NMRP) using dendritic tri‐ and penta‐functional initiators.     

Measurement of Transfer Coefficients to Monomer for n‐Butyl Methacrylate by Molecular Weight Distributions from Emulsion Polymerization

The average kinetic coefficient for chain transfer to monomer 〈k_tr,M〉 in the free‐radical polymerization of n‐butyl methacrylate (BMA) has been determined by the analysis of molecular weight distributions obtained by seeded emulsion polymerization under conditions such that chain transfer to monomer is the dominant chain‐stopping event. Measurements between 40 and 70 °C gave data fitting an Arrhenius‐type relationship with exponential factor E_A = 30 900 ± 4 500 J · mol^?1 and pre‐exponential factor log A = 3.45 ± 0.15. The value for E_A is comparable with published data for chain transfer to monomer from methyl methacrylate (MMA) and n‐butyl acrylate (BA). The A value, however, is 1–3 orders of magnitude smaller, suggesting that there is more hindrance for chain transfer to monomer for BMA than for either MMA or BA.

     

Investigation of Chain Dynamics in Poly(n‐alkyl methacrylate)s by Solid‐State NMR: Comparison with Poly(n‐alkyl acrylate)s

PnAMAs exhibit a local nanophase separation associated with intriguing chain dynamics (Macromol. Chem. Phys. 2005 , 206, 142). PnAMAs of high molar mass, as determined by SEC and MHKS parameters, were investigated in the melt with a recently‐developed solid‐state NMR method (NOE with dipolar filter; Solid State Nucl. Magn. Res. 2005 , 28, 160). The correlation times are assigned to the relaxation of the alkyl nanodomains, as coupled motions of the main chain and hindered local modes in the side chain. Comparison with poly(n‐alkyl acrylates) shows a higher anisotropy of the main chain motions and a better organized local nanophase separation in PnAMAs.

     

Ethylene Polymerization over Homogeneous and Supported Catalysts Based on Bis(imino)pyridine Co(II) Complex: Data on the Number of Active Centers and Propagation Rate Constant

The number of active centers (C_P) and propagation rate constant (k_P) for ethylene polymerization with homogeneous catalyst LCoCl₂ + MAO and supported catalyst LCoCl₂/SiO₂ + Al(i‐Bu)₃, where L is 2,6‐(2,6‐(Me)₂C₆H₃N = CMe)₂C₅H₃N, have been determined using the method of polymerization quenching by radioactive carbon monoxide (¹⁴CO). The unstable rate profile of the reaction was attributed to a decrease in the number of active centers from 0.23 to 0.14 mol · mol^?1(Co) corresponding to an increase in the reaction time from 5 to 15 min, whereas the k_P value remained constant, amounting to 3.5 × 10³ L · mol^?1 · s at 35 °C. A narrow molecular weight distribution of the obtained polyethylene (PE) samples ( = 1.9) testifies that the homogeneous catalyst LCoCl₂ + MAO can be regarded as a single‐site system. The activity of the supported catalyst was stable and noticeably lower than that of the homogeneous catalyst due to the low concentration of the active centers (0.02–0.03 mol · mol^?1(Co)). PE with a broad molecular weight distribution ( = 36) and noticeably higher molecular weight is formed in the presence of the supported catalysts. The activity of the supported catalyst increases sharply at polymerization in the presence of hydrogen. The data obtained on the C_P and k_P values allow suggesting the formation of the “dormant” centers at polymerization without hydrogen and regeneration of the active centers in the presence of hydrogen. The average k_P values for the supported catalyst containing multiple active centers were determined to be 5.9 × 10³ and 10.5 × 10³ L · mol^?1 · s, respectively, at 35 and 50 °C.

     

Mark–Houwink Parameters of Biosynthetic Poly(γ‐glutamic acid) in Aqueous Solution

A combined viscosity–light scattering–gel permeation chromatography (GPC) study was carried out on bacterially produced poly(γ‐glutamic acid) (PGGA). PGGA samples with weight‐average molecular weights ranging from 8×10⁴ up to 8×10⁵ g·mol^–1 dissolved in phosphate buffer at 0.13 M ionic strength were used. It was found that the Mark–Houwink relation is acceptably obeyed, giving K and a values of 1.84×10^–6 dL·g^–1 and 1.16, respectively. As expected, GPC analysis showed that PGGA does not follow the universal calibration plot and that deviations can not be avoided by modifying the ionic strength.     

Comparative Study of Distribution of Active Sites According to Their Stereospecificity in Propylene Polymerization over the Traditional TiCl3 and Supported Titanium–Magnesium Catalysts with Different Composition

The preparative‐temperature rising elution fractionation method is used to obtain comparative data on contents of fractions with different microtacticities for polypropylene (PP) samples prepared using three catalytic systems: the traditional Ziegler–Natta (Z–N) catalyst δ‐TiCl₃ and two types of supported titanium–magnesium catalysts: the “donor‐free” TiCl₄/MgCl₂ catalyst and TiCl₄/MgCl₂·nDBP catalyst (DBP – dibutylphthalate used as an internal donor) at polymerization with the same cocatalyst (AlEt₃) in the absence and presence of an external donor (propyltrimetoxy silane). The separated individual PP fractions are also studied by gel permeation chromatography (molecular weight and molecular weight distribution) and differential scanning calorimetry. The results demonstrate general regularities and differences in the formation of active sites having different isospecificities for the traditional TiCl₃‐based Z–N catalyst and highly active supported titanium–magnesium catalysts.     

EPR Identification of Zr(III) Complexes Formed upon Interaction of (2-PhInd)2ZrCl2 and rac-Me2Si(1-Ind)2ZrCl2 with MAO and MMAO

Reactions of 1 and 2 with MAO and MMAO were monitored by EPR. It was found that MMAO is a stronger reducing agent than MAO. 1 is more prone to reduction than 2 . The reduction of Zr^IV to Zr^III seems to be the essential pathway of some zirconocene catalysts' deactivation. Zr^III species with the following proposed structures can be identified in the 1 /MMAO system: (2-PhInd)₂Zr^III(ⁱBu), (2-PhInd)₂Zr^III(µ-Cl)₂AlⁱBu₂, (2-PhInd)₂Zr^III(µ-Cl)(ⁱBu)AlⁱBu₂, and [(2-PhInd)₂Zr^III]⁺[Me-MAO]⁻. The degree of reduction of Zr^IV species determined by EPR in the catalytic system 2 /MMAO can be masked by the formation of diamagnetic Zr^III/Zr^III dimers. Addition of monomers to the 2 /MAO system promotes reduction ot the zirconium species.

     

Molecular Mass Characteristics of (2‐Benzothiazolon‐3‐yl)acetic Acid–Telechelic Poly(ethylene oxide)s Determined by MALDI‐TOF Mass Spectrometry and SEC

(2‐benzothiazolon‐3‐yl)acetic acid–telechelic poly(ethylene oxide)s (1 100–4 440 Da) with narrow molecular mass distributions (MMD) were analysed by matrix‐assisted laser desorption‐ionisation time‐of‐flight mass spectrometry (MALDI‐TOF MS) and size exclusion chromatography (SEC). The average molecular masses (M̄_n and M̄_w) determined by both methods were compared and a good agreement established. The cutting of the low molecular part of the initial poly(ethylene glycol) MMD during purification and isolation of the produced telechelic poly(ethylene oxide)s was proved. For this reason, the degree of esterification (x) of poly(ethylene glycol) (PEG) with (2‐benzothiazolon‐3‐yl)acetic acid was calculated by MALDI‐TOF MS and SEC, using additional UV data. The two series of x values derived from the M̄_n‐values, determined by the two methods, are very close. All of them are less than unity and the differences between the two types of x values decrease with the PEG molecular mass growth.     

Novel SiO2‐Supported Silyl‐Chromate(Cr)/Imido‐Vanadium(V) Bimetallic Catalysts Producing Polyethylene and Ethylene/1‐Hexene Copolymers with Bimodal Molecular‐Weight Distribution

Novel SiO₂‐supported silyl‐chromate(Cr)/imido‐vanadium(V) (Cr‐imidoV) bimetallic catalysts for ethylene and ethylene/α‐olefin polymerization are investigated. These catalysts are prepared using the residual surface hydroxyl groups in SiO₂‐supported imido‐vanadium catalysts to further support bis(triphenylsilyl) chromate (BC) in order to get the merits from both the SiO₂‐supported imido vanadium catalyst and the SiO₂‐supported silyl chromate S‐2 catalyst. By investigation of the polymerization behavior and the microstructures of their polymers, several vital factors such as the addition amount of imido vanadium active centers and the dosage of 1‐hexene in the ethylene homopolymerization and ethylene/1‐hexene copolymerization are systematically investigated. Compared with the traditional S‐2 catalyst and our previously reported SiO₂‐supported silyl‐chromate(Cr)/vanadium(V)‐oxide (Cr‐V) bimetallic catalyst, the novel Cr‐imidoV bimetallic catalysts show even higher activity and better 1‐hexene incorporation ability, together with higher molecular weight (MW) and bimodal molecular‐weight distribution (MWD).

     

Kinetic Study of Ethylene Polymerization Over Supported Bis(imino)pyridine Iron (II) Catalysts

Summary: The number of active centers (C_P) and propagation rate constants (k_P) for polymerization of ethylene with supported catalysts LFeCl₂/SiO₂, LFeCl₂/Al₂O₃ and LFeCl₂/MgCl₂ (L = 2,6‐(2,6‐(Me)₂C₆H₃NCMe)₂C₅H₃N), activated by an Al(i‐Bu)₃ co‐catalyst, were determined by a method of polymerization inhibition with radioactive ¹⁴CO. In contrast to homogeneous systems based on LFeCl₂, the supported catalysts are highly active and stable in ethylene polymerization at 70–80 °C. In the presence of hydrogen, the activity of the supported catalysts substantially increases (2–4 fold). The data obtained on the effect of hydrogen on the calculated C_P and k_P values suggests that for ethylene polymerization without hydrogen, the “dormant” active centers are formed in the catalytic systems. A scheme for the formation of these “dormant” centers and their reactivation in presence of hydrogen is suggested. For the investigated supported catalysts the C_P values were found to be only 2 to 4% of the total iron complex content in the catalysts. The k_P value for the catalysts prepared using different supports (SiO₂, Al₂O₃ and MgCl₂) were close (3.2 × 10⁴ to 4.5 × 10⁴ L · (mol · s)⁻¹ at 70 °C). The support composition affects neither the molecular mass (MM) nor the molecular mass distribution (MMD) of the polymers produced. The obtained C_P and k_P values and data on the polymer MM and MMD lead to conclusion that the nature of the support has almost no effect on the structure of the active centers and the distribution of their reactivity.

Effect of support on the MMD of PE produced over supported LFeCl₂ catalysts.     

Gel Formation and Molecular Characteristics of Poly(N‐isopropylacrylamide) Prepared by Free‐Radical Redox Polymerization in Aqueous Solution

The molecular characteristics of poly(N‐isopropylacrylamide) (PNIPA), prepared by free‐radical polymerization using an aqueous redox initiator and reaction conditions comparable to those used in the synthesis of nanocomposite gels, were investigated by altering the monomer concentration ([NIPA]) and the polymerization temperature (T_p) across the transition temperature (LCST). When T_p<LCST, there is a critical [NIPA] (=n*) above which PNIPA partially forms gels in the absence of a chemical crosslinker, and the gel fraction increases with increasing [NIPA] and decreasing T_p. In the range of n<n*, the molecular weight of soluble PNIPA correlated well with [NIPA]. When T_p>LCST, gels were not formed regardless of [NIPA]. The structure and mechanism of formation of self‐crosslinked PNIPA gels are discussed.

     

Poly(N‐hydroxyethylacrylamide) Prepared by Atom Transfer Radical Polymerization as a Nonionic,Water‐Soluble,and Hydrolysis‐Resistant Polymer and/or Segment of Block Copolymer with a Well‐Defined Molecular Weight

N‐Hydroxyethylacrylamide (HEAA) was polymerized using the atom transfer radical polymerization (ATRP) with ethyl 2‐chloropropionate (ECP), copper(I) chloride (CuCl), and tris[2‐(dimethylamino)ethyl]amine (Me₆TREN) in ethanol/water, producing poly(N‐hydroxyethylacrylamide) (PHEAA) with well‐defined molecular weights. The thermogravimetric analysis (TGA) indicated that the obtained PHEAA broadly decomposed with a two‐stage weight loss. The first loss was due to the decomposition of the hydroxyethyl groups, which started at temperatures ranging from 249.2 to 277.1 °C. The remaining polyacrylamide backbones started to decompose at temperatures ranging from 352.5 to 383.4 °C. The differential scanning calorimetry (DSC) indicated that PHEAA had a glass transition temperature (T_g) ranging from 70.6 to 117.8 °C. The ability of the obtained PHEAA as a prepolymer to initiate other acrylamide derivatives is described. N,N‐Dimethylacrylamide (DMAA), N‐acyloylmorpholine (NAM), and N‐[3‐(dimethylamino)propyl]acrylamide (DMAPAA) were subsequently added to the solutions after the polymerization of HEAA with ECP/CuCl/Me₆TREN, producing the corresponding block copolymers.

     

Molecular Weight Distribution Characteristics (of a Polymer) Derived from a Stretched‐Exponential PGSTE NMR Response Function—Simulation

Assuming the signal response in a pulsed gradient stimulated echo (PGSTE) experiment (on a polymer) to be described by a simple stretched‐exponential function (SEF) and knowing the scaling law between diffusivity and molecular weight, the molecular weight distribution (MWD) characteristics (kurtosis, skewness, moment, and width) are derived and compared to the corresponding distribution characteristics obtained by a log‐normal function fit (to the same MWD). Also, the challenge involved in obtaining a reliable weight average molecular weight from an SEF response function is discussed.     

1H and 13C NMR Study of the Intermediates Formed by (Cp‐R)2ZrCl2 Activation with MAO and AlMe3/[CPh3][B(C6F5)4]. Correlation of Spectroscopic and Ethene Polymerization Data

Using ¹H and ¹³C NMR spectroscopy, cationic intermediates formed by activation of (Cp‐R)₂ZrCl₂ (R = nBu, tBu and 1,2,3‐Me₃) with MAO in toluene were monitored at Al/Zr ratios from 50 to 1 000. The catalysts (Cp‐R)₂ZrCl₂/AlMe₃/CPh₃⁺B(C₆F₅)₄^? (nBu, tBu and 1,2,3‐Me₃) were also studied for comparison of spectroscopic and polymerization data with MAO based systems. Complexes of type (Cp‐R)₂ZrMe⁺ ← Me^?‐Al?MAO ( IV ) with different Me‐MAO^? counter anions have been identified in the (Cp‐R)₂ZrCl₂/MAO systems at low Al/Zr ratios. At Al/Zr ratios of 200–1 000, the complex [(Cp‐R)₂Zr(μ‐Me)₂AlMe₂]⁺ Me‐MAO^? ( III ) dominates in all MAO‐based reaction systems. Ethene polymerization activity strongly depends on the Al/Zr ratio (Al/Zr = 200–1 000) for the systems (Cp‐nBu)₂ZrCl₂/MAO and (Cp‐tBu)₂ZrCl₂/MAO, while it is virtually constant in the same range of Al/Zr ratios for the catalytic system (Cp‐1,2,3‐Me₃)₂ZrCl₂/MAO. The data obtained are interpreted on the assumption that complex III is the actual precursor of active centers of polymerization in MAO based systems.

Formation of cationic intermediates by activation with MAO.