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.     

Ionic π‐Conjugated Polyelectrolytes by Catalyst Free Polymerization of Bis(pyridyl)acetylenes and Bis[(pyridyl)ethynyl]benzenes

The spontaneous, catalyst free polymerization of four monomers of the bis(pyridyl)acetylene and bis[(pyridyl)ethynyl]benzene types containing either 2‐pyridyl or 4‐pyridyl groups via activation with benzyl bromide leads to ionic π‐conjugated polyacetylene‐type polyelectrolytes (CPEs). All polymers are characterized by means of NMR, IR, UV/vis and photoluminescence spectroscopies, thermogravimetric analysis (TGA) and matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI‐TOF MS). The position of the pyridyl groups in the monomer influences the degree of quaternization and the extent of conjugation of CPEs. Monomers with 4‐pyridyl groups provide CPEs with a low extent of quaternization [N⁺/(N⁺ + N) = 0.27–0.34] and high extent of conjugation. On the other hand, the CPEs derived from 2‐pyridyl‐containing monomers are highly quaternized [N⁺/(N⁺ + N) = 0.77–1.00], however, possess lower conjugation of the main chains. The mechanism assuming quaternization and polymerization as competitive reactions is proposed to explain the difference in the extent of quaternization of CPEs. Prepared CPEs i) are well soluble in polar solvents, e.g., water, methanol, dimethyl sulfoxide, and dimethylformamide, ii) exhibit photoluminescence (emission in the violet to yellow region), and iii) possess high thermal stability.

     

Polymerization of Methyl Acrylate by a 2,6‐Bis(2‐benzimidazyl)pyridine Zirconium Dichloride/MAO Catalyst System

Summary: A novel non‐metallocene Zr(IV) complex bearing a bianionic form of the ligand 2,6‐bis(2‐benzimidazolyl)pyridine is synthesized. This Zr complex is an active catalyst for the polymerization of MA via coordination polymerization in the presence of methylaluminoxane MAO. The activity and MWD are increased as the polymerization temperature increases. The maximum activity is observed at Al/Zr molar ratio of 100 and the deactivation is shown above 100, resulting from an inactive bimetallic complex between catalyst and free TMA presented in MAO. Decrease in MWD is observed with higher MAO concentration due to its role in chain transfer during the chain propagation.

The reaction of the ligand and catalyst synthesis.     

EPDM Synthesis by the Ziegler Catalyst Cp*TiMe3/B(C6F5)3

The utilization of the Ziegler catalyst Cp*TiMe₃/B(C₆F₅)₃ for the terpolymerization of ethylene, propylene and 5‐ethylidene‐2‐norbornene to give EPDM is investigated, and the major factors affecting yields, molecular weights, molecular weight distributions and compositional distributions of the EPDM polymers are assessed. High molecular weight polymers with narrow molecular weight distributions are obtained at ˜18°C.     

Spontaneous tumors in aging (C57BL/6N x C3H/HeN)F1 (B6C3F1) mice

Spontaneous tumors in untreated (C57BL/6N x C3H/HeN)F1 (B6C3F1) mice used as controls in carcinogenicity tests were recorded. In both sexes, the development of spontaneous tumors was age-related. In 244 male mice, the most common tumors were hyperplastic nodules of the liver, hepatocellular carcinomas, malignant lymphomas/leukemias, lung adenomas, and adenocarcinomas. In 246 female mice, the most common tumors were malignant lymphomas/leukemias, pituitary adenomas, neoplastic nodules of the liver, hepatocellular carcinomas, and lung adenomas. Hepatocellular carcinomas metastasized in 20.3% of the animals with these tumors. Few other tumors except malignant lymphomas and leukemias metastasized. Various tumors of other organs and/or tissues were found at low incidences.     

Isospecific Propylene Polymerization Using the [ArN(CH2)3NAr]TiCl2/Al(iBu)3/Ph3CB(C6F5)4 Catalyst System in the Presence of Cyclohexene

Propylene polymerization was carried out using the [ArN(CH₂)₃NAr]TiCl₂ (Ar = 2,6‐iPr₂C₆H₃)/Al(iBu)₃/Ph₃CB(C₆F₅)₄ catalyst system in the presence of cyclohexene. It was found that isospecific polymerization is promoted by adding cyclohexene even at low propylene concentration. It was also indicated that a considerable number of isospecific active species retain the metal‐polymer bond. Based on this fact, isotactic poly(propylene)‐block‐poly(1‐hexene) could be obtained.     

Ethylene/propene copolymerization in the presence of the homogeneous catalyst system Ti(Oi-C3H7)4/Al(C2H5)2F

The behaviour of the homogeneous catalyst system Ti(Oi-C₃H₇)₄/Al(C₂H₅)₂F in ethylene/propene copolymerization was studied. The copolymer structure is discussed in view of the stereoregulation mechanism previously proposed for vanadium-based homogeneous catalyst systems.     

A combined NMR and electron spin resonance investigation of the (C5(CH3)5)Ti(CH2C6H5)3/B(C6F5)3 catalytic system active in the syndiospecific styrene polymerization

The reaction of (C₅(CH₃)₅)Ti(CH₂C₆H₅)₃ with B(C₆F₅)₃ in chlorobenzene at 25°C produces a mixture of [(C₅(CH₃)₅)Ti(CH₂C₆H₅)₂]⁺ [B(CH₂C₆H₅)(C₆F₅)₃]^? ( 1 ) and Ti(III) complexes which have been characterized by NMR and electron spin resonance (ESR) spectroscopy, respectively. Spectroscopic data combined with polymerisation activity measurements suggest that a Ti(III) complex is the active species in the styrene syndiospecific polymerisation.     

Characteristics and Mechanism of Styrene Cationic Polymerization in Aqueous Media Initiated by Cumyl Alcohol/B(C6F5)3

Styrene cationic polymerizations initiated by cumyl alcohol (CumOH)/B(C₆F₅)₃ are systematically studied in aqueous suspension and emulsion. Theoretical calculations and experimental research suggest that CumOH/B(C₆F₅)₃ has higher initiating activity than H₂O/B(C₆F₅)₃. During emulsion polymerization of styrene, molecular weight and polymerization rate decrease with the addition of surfactants. These polymerization processes share the same features. Specifically, all elemental reactions (initiation, propagation, and termination) in aqueous media occur at the droplet interface. End structure analysis indicates that chain transfer reactions to water and a‐proton elimination and chain transfer reactions to monomer occur. The possible mechanism for the styrene cationic polymerization in aqueous media is demonstrated.     

On the 1,4‐cis‐Polymerization of Butadiene with the Highly Active Catalyst Systems Nd(C3H5)2Cl·1.5 THF/Hexaisobutylaluminoxane (HIBAO), Nd(C3H5)Cl2· 2 THF/HIBAO and Nd(C3H5)Cl2·2 THF/Methyl‐aluminoxane (MAO) – Degree of Polymerization,Polydispersity, Kinetics and Catalyst Formation

The allylneodymium chloride complexes Nd(C₃H₅)₂Cl·1.5 THF and Nd(C₃H₅)Cl₂·2 THF can be activated by adding hexaisobutylaluminoxane (HIBAO) or methylaluminoxane (MAO) in a ratio of Al/Nd = 30 for the catalysis of butadiene 1,4‐cis‐polymerization. A turnover frequency (TOF) of about 20 000 mol butadiene/(mol Nd·h) and cis‐selectivity of 95–97% are achieved under standard conditions ([BD]₀ = 2 m, 35°C, toluene). Molecular weight determinations indicate a low polydispersity (M̄_w (LS)/M̄_n (LS) = 1–1.5), the formation of only one polymer chain per neodymium and the linear increase of the degree of polymerization (DP) with the butadiene conversion, as observed for living polymerizations. First indications of chain‐transfer reaction occur only at the highest conversion or degree of polymerization. The rate law r_P = k_P[Nd][C₄H₆]^1.8 is derived for the catalyst system Nd(C₃H₅)₂Cl·1.5 THF/HIBAO and for the system Nd(C₃H₅)Cl₂·2 THF/MAO the rate law r_P = k_P[Nd] [C₄H₆]² with k_P = 3.24 L²/(mol²·s) (at 35°C). Taking into account the Lewis acidity of the alkylaluminoxanes and the characteristic coordination number of 8 for Nd(III) in allyl complexes the formation of an η³‐butenyl‐bis(η⁴‐butadiene)neodymium(III) complex of the composition [Nd(η³‐RC₃H₄)(η⁴‐C₄H₆)₂(X‐{AlOR}_n)₂] is assumed to be a single‐site catalyst for the chain propagation by reaction of the coordinated butadiene via the π‐allyl insertion mechanism and the anti‐cis and syn‐trans correlation to explain the experimental results.     

Synthesis of Terminally Functionalized Isotactic Poly(propylene) with a [ArN(CH2)3NAr]TiCl2 (Ar = 2,6‐iPr2C6H3) – MAO Catalyst System

Syntheses of terminally hydroxylated and iodinated isotactic poly(propylene)s were carried out by the reactions of oxygen and iodine with polymer–Al bonds produced in propylene polymerization with [ArN(CH₂)₃NAr]TiCl₂ (Ar = 2,6‐ⁱPr₂C₆H₃) combined with methylaluminoxane (MAO) as a cocatalyst. The resulting isotactic polymer (ca. 45 wt.‐%) was separated from the atactic one by extraction with boiling ether. From ¹³C NMR measurements of the isotactic fraction, it was found that the content of the terminally functionalized isotactic poly(propylene) was more than 80 mol‐% in all cases.     

Reaction of Carbon Monoxide with Living PP Prepared with a Cp2ZrMe2/B(C6F5)3 Catalyst System

The reaction between carbon monoxide (CO) and the living Zr‐poly(propylene) (Zr‐PP) bond, which was prepared with Cp₂ZrMe₂/B(C₆F₅)₃/AlOct₃ catalyst system at –78°C, was investigated. The reaction products were analyzed by means of IR, ¹H‐NMR and GPC. Under the reaction conducted at –78°C, it could be found that CO was quantitatively incorporated into the Zr‐PP bond to generate a terminal aldehyde group. And when the reaction was started at –78°C and gradually warmed up to room temperature, a ketone carbonyl in the polymer chain was formed.     

Copolycondensation of Regular Functional Silane and Siloxane in Aqueous Emulsion Using B(C6F5)3 as a Catalyst

The copolycondensation of siloxane and silane bearing hydrido and methoxy groups, respectively, was carried out in a surfactant‐free aqueous emulsion, at room temperature and using B(C₆F₅)₃ as a water‐tolerant Lewis acid. Several characterization techniques, including triple detection SEC, ²⁹Si NMR and MALDI‐TOF, confirmed the generation of linear polymers (no macrocycles), of average molar masses ranging between 30 and 80 000 g · mol^?1, and bearing silanol end‐groups. Colloidal evolution with time showed that a stable surfactant‐free emulsion was generated before some coalescence occurs by decreasing the content of silanol groups suspected to stabilize the emulsion. The kinetics of reaction was followed by SEC, and revealed the generation of small cycles, along with linear oligomers, before converting them to poly(dimethylsiloxane) chains. A tentative mechanism, where ring‐opening polymerization of the most stranded cyclosiloxane and polycondensation of polymer chains are considered, is proposed.

     

Molecular Structure of 113C‐C2H4/C3H6 Copolymers Prepared in the Presence of Half Sandwich Titanium Methyl – B(C6F5)3 Catalysts

Summary: Copolymers of propylene with 1¹³C‐ethylene (99% isotopic purity) have been prepared in the presence of Cp*Ti(CH₃)₃ – B(C₆F₅)₃ (I) or CpTi(CH₃)₃ – B(C₆F₅)₃ (II) (Cp = cyclopentadienyl, Cp* = pentamethylcyclopentadienyl). ¹³C NMR analysis confirms previous findings that propylene polymerization in the presence of I is highly regioselective and somewhat isoselective, while catalyst II produces regioblock polypropylene. In the presence of II, polymerization is slightly syndioselective and the average size of the primary regioblocks seems larger than that of the secondary ones. Moreover, secondary insertion seems more syndioselective than the primary.

¹³C NMR spectra of samples I.2 and II.2.     

Polymerization of styrene with the VOCl3/Li(iC5H11) catalyst system

The polymerization of styrene with the VOCl₃/Li(iC₅H₁₁) catalyst system has been studied. Rates of polymerization fall sharply with increase in Li/V ratio; the molecular weights, however, show a maximum at Li/V = 1. Polymerization is first order with respect to catlyst as well as monomer concentrations. Activation energy was found to be 5.67 kcal/mole. Zinc diethyl acts as chain transfer agent. There was no effect of trans-stilbene on molecular weights as well as on rate of polymerization. Valence of vanadium at Li/V molar ratio 1 is 4.12 and it decreases with increase in ratio.     

Role of C5a in the induction of tumoricidal activity in C3H/HeJ (Lpsd) and C3H/OuJ (Lpsn) macrophages

Thioglycollate-elicited macrophages from C3H/HeJ (Lpsd) and C3H/OuJ (Lpsn) mice were cultured in a two-signal, tumoricidal assay using recombinant interferon-gamma (rIFN-gamma) as the "priming" signal and recombinant human C5a (rC5a) as the "trigger" signal. These experiments were compared directly with a well established, two-signal tumoricidal assay in which rIFN-gamma was used as the "priming" signal and protein-rich, butanol-extracted lipopolysaccharide (But-LPS) as the "trigger" signal. These studies showed that rIFN-gamma-primed macrophages can be triggered in a dose-dependent manner by rC5a to effect high levels of tumoricidal activity. Maximum levels of cytotoxicity achieved using this endogenously produced, biologically active peptide as a "trigger" signal were comparable to those obtained using But-LPS. Moreover, experiments in which anti-C5 antibody was included in macrophage cultures stimulated with rIFN-gamma and But-LPS showed a significant reduction (P less than .05) in tumoricidal activity. Because LPS has been shown to induce macrophage C5 production and enzyme release, these findings suggest that macrophage-derived C5 is locally converted to C5a (or some other biologically active C5 cleavage fragment), which functions as an autocrine trigger signal for the induction of tumoricidal activity. In summary, these data suggest 1) that rC5a can provide a "second signal" to rIFN-gamma-primed murine macrophages for the induction of tumoricidal activity and 2) that macrophage-derived C5 or C5a may represent an autocrine signal induced by exogenous "trigger signals."     

Syndiotactic styrene‐butadiene block copolymers synthesized with CpTiX3/MAO (Cp = C5H5, X = Cl,F; Cp = C5Me5, X = Me) and TiXn/MAO (n = 3, X = acac; n = 4, X = O‐tert‐Bu)

Copolymers sPS‐B consisting of blocks of syndiotactic polystyrene (sPS) and polybutadiene (B) have been prepared using CpTiX₃ (Cp = C₅H₅, X = Cl, F; Cp = C₅Me₅, X = Me) and TiX_n (n = 3, X = acetylacetonate (acac); n = 4, X = O‐tert‐Bu) activated with methylaluminoxane (MAO). If proper conditions are used, copolymers containing a range of styrene and butadiene molar fractions can be prepared. Structural analysis of these copolymers by means of ¹³C NMR spectroscopy allowed the assignment of different monomer diads (SS, SB, BB; S = styrene, B = butadiene) and the calculation of reactivity ratio products r₁·r₂. Differential scanning calorimetry (DSC) analysis further confirmed the block‐like structure of these copolymers. The melting points (T_m) of syndiotactic styrene sequences decrease as the styrene molar fraction decreases, whereas the glass transition temperature (Tg) increases with decreasing butadiene molar fraction in the copolymer. The polydispersity values (M_w/M_n) determined by GPC suggest that these copolymers are produced by a single site catalyst.     

Comparison of Ethylene Copolymerization with Norbornene and 5-Norbornene-2-methanol by Using Ph2C(Cp)(Flu)ZrCl2/MAO

Both cyclic olefin copolymer (COC) and functionalized polyolefins are high-performance polyolefin materials with different outstanding properties. The introduction of functional groups into COC has the potential to yield materials that combine the advantages of both. In this work, ethylene copolymers with norbornene (NBE) or 5-norbornene-2-methanol (NBMO) are synthesized by using a metallocene catalyst. The activity and the molecular weight of copolymer of the former is much higher than that of the latter. A joint deactivation-chain transfer mechanism is proposed to interpret these observations. Chain transfer is further discussed. Through regression analysis, it is considered that the chain transfer mode of the two comonomers is the same. Three methods for the calculation of NBMO incorporation are proposed and compared, and a more suitable method is obtained, on the basis of the resonance assignment. The comparison of the copolymerization of ethylene with NBE and NBMO may indicate that NBMO has a higher coordination probability but a slower insertion rate compared to NBE.