Synthesis of high molecular weight polyisobutylene via cationic polymerization at elevated temperatures

A novel simple but effective initiating system of H2O/AlCl3 /veratrole (VE) has been developed to synthesize high molecular weight polyisobutylene (PIB) at elevated temperatures via cationic polymerization of isobutylene (IB) in solvent mixture of hexane/methylene dichloride (n-Hex/CH2Cl2 = 2/1, V/V). VE played very important roles in decreasing cationicity of the growing chain ends, suppressing side reactions of chain transfer and termination during polymerization, leading to production of high molecular weight PIBs. PIBs with high yields, having very high weight-average molecular weight (Mw ) of 1117000 and 370000 g/mol could be synthesized with H2O/AlCl3 /VE initiating system at VE concentration of 5.4 mmol/L at 80 and 60℃ respectively. Molecular weight of PIB increased remarkably with increasing VE concentration. The reaction order with respect to VE concentration was determined to be 3.52 via FTIR spectroscopy in combination with a diamond tipped attenuated total reflectance (ATR) immersion probe. The negative reaction order of VE was consistent with its retarding effect on IB polymerization by interacting with the propagating species. Molecular weight of PIB decreased with increasing polymerization temperature. The activation energy for polymerization degree (EDP ) could be determined to be around 23 kJ/mol when VE concentration was 5.4 mmol/L or 6.4 mmol/L.     

The phase diagram of fullerene C60 at high temperatures and pressures

Experimental and literature data were used to calculate the Gibbs energies of polymerized C₆₀ phases and construct the equilibrium T-p phase diagram of fullerene C₆₀ at temperatures from 0 to 1000 K and pressures from 0 to 8 GPa. The diagram contains stability regions of the orthorhombic, tetragonal, and rhombohedral polymerized C₆₀ phases and primitive cubic (PC) and face-centered cubic (FCC) nonpolymerized C₆₀ phases. The orthorhombic phase (linear polymer) is an equilibrium phase at 298 K and 1 bar and in the adjacent region. The equilibrium line observed experimentally (FCC C₆₀—orthorhombic phase) is well described by the phase diagram. The optimum temperatures and pressures of the synthesis of polymerized phases are determined by kinetic rather than thermodynamic parameters.     

Emulsion polymerization of styrene under high pressure

Summary The emulsion polymerization of styrene was studied at 40 °C over a pressure range of 1 to 1000 bar. By measuring the ratio of the overall reaction rate under high pressure and at atmospheric pressure, the activation volume for the prouagation was obtained as –23.5 cm³/mol which was rather smaller than the literature values. The underestimation by the method of emulsion polymerization would be due to the character of polymerization processes and the emulsion polymerization method is not appropriate to determine the accurate value of the activation volume of propagation reactions.

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Zusammenfassung Es wird die Emulsionspolymerisation von Styrol bei 40 °C über den Druckbereich von 1 bis 1000 bar untersucht. Durch Messung des Verhältnisses der Reaktionsgeschwindigkeit unter hohem Druck und bei Atmosphärendruck wurde das Aktivierungsvolumen für die Ausbreitungsgeschwindigkeit zu –23,5 cm³/mol gefunden, ein Werr, der ziemlich kleiner als die Literaturwerte ist, Die Unterschätzung bei der Methode der Emulsionspolymerisation dürfte dem Charakter des Polymerisationsprozesses zuzuschreiben sein, und die Emulsionspolymerisation ist nicht geeignet, den exakten Wer für das Aktivierungsvolumen zu erhalten.

     

Extremely narrow-dispersed high molecular weight polyethylene from living polymerization at elevated temperatures with o-F substituted Ti enolatoimines

With a new titanium imineenolato complex, ethylene is polymerized in an unprecedented living fashion affording a polymer with a high molecular weight (Mn > 10(5) g mol-1) and an extremely narrow distribution (Mw/Mn 1.01) at the same time; the living character is also retained even at an elevated temperature of 75 degrees C, and blockcopolymers are accessible.     

γ-radiation-initiated polymerization of bulk styrene at high pressure

The polymerization of styrene in bulk at pressures up to 273 MPa and temperatures between 3 and 49°C with the use of γ-radiation as the initiator has been studied. The polymerization rate and the molecular weight of the polymer increased with increasing pressure; the molecular weight increased at a slightly faster rate. The difference in the rate is a theoretical expectation which has not previously been observed because chain-transfer reactions obscure the effect in chemically initiated systems. A small but significant retardation of the initiation reaction occurs as the pressure is increased. The results of previous workers are critically reviewed. Chain transfer at 25°C for pressures below 220 MPa is negligible when γ-radiation is the initiator. The activation energy for bulk polymerization decreased with increasing pressure from 28.1 kJ/mole at 0.1013 MPa to 22.3 kJ/mole at 203 MPa. Volumes of activation at 25°C for 0.1013 < p < 273 MPa were calculated to be Initiation, +4.0 < ΔV < +4.4 cm³/mole; polymerization; ?Δ = ?20.9 cm³/mole; degree of polymerization; ΔV = ?25.3 cm³/mole; propagation/termination; ?ΔV = ?22.7 cm³/mole.     

Controlled cationic polymerization of styrene using AlCl3OBu2 as a coinitiator: Toward high molecular weight polystyrenes at elevated temperatures

The controlled cationic polymerization of styrene using CumOH/AlCl₃OBu₂/Py initiating system in a mixture CH₂Cl₂/n‐hexane 60/40 v/v at ?40 and ?60 °C is reported. The number‐average molecular weights of the obtained polystyrenes increased with increasing monomer conversion (up to M_n = 85,000 g mol^?1) although experimental values of M_n were higher than the theoretical ones at the beginning of the reaction that was ascribed to slow exchange between reversible‐terminated and propagating species. The molecular weight distribution became narrower through the reaction and leveled of at the value of M_w/M_n = 1.8–2.0. A kinetic investigation revealed that the rate of polymerization was first‐order in AlCl₃OBu₂ concentration meaning that monomeric counteranion (AlCl₃OH^? or AlCl) involved in the initiation and propagation steps of the reaction. It was also found that the rate of polymerization decreased with lowering temperature, which could be attributed to a decrease in concentration of free Lewis acid (AlCl₃), the true coinitiator of polymerization, because of an increase in the tightness of its complex with dibutyl ether. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3736–3743, 2010     

Ultracentrifugal equilibrium measurement of high polymer solutions at elevated temperatures

To investigate the solution properties of polyethylene, which has the simplest structure of the vinyl polymers, experiments were made with a magnetically suspended equilibrium ultracentrifuge. Preliminary studies were carried out with a polystyrene–chloroform system at 25°C. and a polystyrene–methylcyclohexane system at 68°C. (which is close to the theta temperature) in order to check the difficulties involved in the flotation equilibrium in the former case and the high temperature measurement in the latter. However, no trouble was encountered in either system, and the results were discussed and compared with earlier results for polystyrene solutions. It was found that chloroform is a good solvent for polystyrene, and the measured weight-average molecular weight is somewhat smaller than the value obtained in a theta solvent. After overcoming some technical difficulties involved in studies at higher temperatures, we carried out experiments on polyethylene in α-chloronaphthalene at 130°C. The results are considered reasonable by comparison with results obtained by other methods. The sample employed, Marlex 50 of melt index 0.7, has a wide molecular weight distribution: i.e., M_z/M_w = 5.2 and M_z+1/M_z = 2.4.     

Radiation-induced solid-state polymerization of trioxane under high pressure

The in-source polymerization of trioxane in the solid state was investigated over a wide range of temperature and pressure, i.e., from 30 to 140°C and up to 7000 kg/cm², respectively. In the polymerization that was carried out slightly below the melting point under pressure, the higher the pressure, the higher the rate of polymerization. It was confirmed that the maximum rate of solid-state polymerization of trioxane occurs near the melting points, even under elevated pressure. The rate of polymerization decreased with increasing pressure at constant temperature. The shape of the time–conversion curves may be classified into two types, i.e., one which is typical of high pressure and low temperature, and the other which is typical of low pressure and high temperature. Changes in the shape of the conversion—intrinsic viscosity curves occurred coincidentally. Thus, three regions for the different “polymerization characteristic” were determined as functions of polymerization temperature and pressure. Explanations are given for the above-mentioned polymerization characteristic.     

Radiation-induced polymerization of sodium allylsulfonate at high pressure

Irradiation of sodium allylsulfonate in aqueous solution at high pressure (up to 9000 kg/cm²) gave a deliquescent white powder which is insoluble in organic solvent. The product was addition polymer of allylsulfonate from the high-resolution NMR and infrared spectra. The rate of polymerization was proportional to the third and second powers of monomer concentration in the initial and later stages, respectively. From the high dependence of the rate on monomer concentration, the reaction was deduced to proceed in an associated monomer or micelle. The rate of polymerization was increased by addition of sodium chloride. The G value for monomer consumption was about 10⁴ at high pressure, which suggests that the degradative chain transfer is not important in the polymerization. Overall activation volumes were ?7 and ?5 ml/mole in the initial and later stages, respectively.     

Reaction of hydrogen gas with C60 at elevated pressure and temperature: hydrogenation and cage fragmentation

Products of the reaction of C(60) with H(2) gas have been monitored by high-resolution atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry (APPI FT-ICR MS), X-ray diffraction, and IR spectroscopy as a function of hydrogenation period. Samples were synthesized at 673 K and 120 bar hydrogen pressure for hydrogenation periods between 300 and 5000 min, resulting in the formation of hydrofullerene mixtures with hydrogen content ranging from 1.6 to 5.3 wt %. Highly reduced C(60)H(x) (x > 36-40) and products of their fragmentation were identified in these samples by APPI FT-ICR MS. A sharp change in structure was observed for samples with at least 5.0 wt % of hydrogen. Low-mass (300-500 Da) hydrogenation products not observed by prior field desorption (FD) FT-ICR MS were detected by APPI FT-ICR MS and their elemental compositions obtained for the first time. Synthetic and analytical fragmentation pathways are discussed.     

Radiation-induced polymerization of hexafluoropropylene at high temperature and pressure

The radiation-induced polymerization of hexafluoropropylene was studied in the pressure and temperature ranges of 4,500–15,000 atm. and 100–230°C., respectively. Retardation was a serious problem; data thought to apply to the unretarded polymerization are summarized below. At 1,500 rad/hr. the polymerization rate was 15%/hr. at 230°C. and 15,000 atm. The activation enthalpy and volume are 9.5 kcal./mole and ?10 cc./mole, respectively. The rate varies as the square root of the radiation intensity. The largest intrinsic viscosity of the polymer is 2.0 dl./g.; values increase with temperature and pressure. At 130°C. and 10,000 atm. the intrinsic viscosity was the same at two radiation intensities.     

Radiation-induced polymerization of 3,3,4,4,5,5,5-heptafluoropentene-1 at high pressure

A study was made of the radiation-induced polymerization under pressure of 3,3,4,4,5,5,5-heptafluoropentene-1. Polymerization rates increase with pressure (activation volume equals ? 11 cc/mole) and temperature (activation enthalpy equals 6.5 kcal/mole) in liquid phase. At 13800 atm and 25°C, freezing occurs; the polymerization rate in the solid is very small. In liquid phase polymerization can continue for many hours after the irradiation is terminated. An active species is formed by radiation which initiates polymerization in the dark period.     

Thermometric titrations at elevated temperatures

The oxidizing power of hexacyanoferrate(III) in alkaline conditions is wellknown. Unfortunately many if its oxidation reactions are too slow at room temperatures for direct titrimetric procedures. A method has been developed for the determination of millimolar amounts of selenium(IV), arsenic(III), antimony(III), chromium(III), and thallium(I) using thermometric titrimetry at approximately 330 K. The reproducibility and accuracy of the method are approximately 1%.     

Performance of bio-mortar under elevated temperatures

The microbially induced calcite precipitation was used to bind sand grains, yielding consolidated material known as bio-mortar. An aerobic, urease-active and nonpathogenic Sporosarcina pasteurii microorganism was used for the induction of calcite precipitation. Three different temperatures (250, 500 and 750 °C) were applied to examine the firing resistivity of bio-mortar. The results showed that the organic fiber of died bacterial cells completely dissociates at 500 °C, causing a moderate compressive strength reduction and mass loss increment in bio-mortar. The exposure of bio-mortar to 750 °C leads to a significant compressive strength regression, due to the thermal decomposition of CaCO₃ as confirmed by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis and differential thermal analysis (TG and DTA) as well as scanning electron microscopy.

     

On the extent of polymerization of liquid sulfur at very high temperatures

The extent of polymerization of liquid sulfur up to 731 K has been obtained using Raman scattering. The data reveal the absence of a maximum in the polymerization curve. The obtained results are discussed in the spirit of computer simulations that suggest the existence of a maximum which depends on the bond breaking energy.     

Transformations of cellulose at elevated temperatures

Summary The presence of 2–20% of glucose in cellulose during its thermal degradation results in a reduction in the yield of levoglucosan from 55–60% to 30%.