Polymerization at various temperatures

Figure 5. Conversion profiles for styrene seed latex polymerization at various temperatures. Solid curves are theoretical predictions and data points are experimental results (YD) a0 = 0.458 (A) a0 = 1.82 (O) a0 = 7.71)...

Polymerization at various temperatures allows the calculation of the overall activation energy of polymerization to be between 20 and 40 kg/mol for the system Ti(OEt) 4/MAO. The catalysts are stable for at least 2 h. Activity which is low below 30 °C is enhanced exponentially at temperatures up to 70 °C. The monomer concentration has a major effect on the polymerization activity. 

Melt Viscosity vs. Shear Rate for Suspension PVC s Polymerized at Various Temperatures. 

Figure 47 DSC Analysis on epoxy adhesives polymerized at various temperatures during 30 min. It shows that at 150°C/30 min the polymerization was completed. At the other temperatures, residual enthalpy proves that polymerization was not finished.

Few results have been reported on the effect of temperature on stereoelection. Propylene oxide was polymerized at various temperatures. It was found that the overall stereoelectivi-ty is not modified when the temperature is changed from +80 to -8° [13]. However the rate of polymerization is decreased (by a factor of 10 ) and the distribution of different fractions in the polymer modified. With a lowering of the temperature the proportion of crystalline fraction is increased up to 70% (Figure 11). The behaviour of propylene sulfide is similar to that of propylene oxide, r being not modified between +30° and -30°, while the crystallinity was increased in the latter case [24]. 

When an acetone solution of the monomeric complex, [NiBr2(P(C2H4CN)3)2]/ was allowed to polymerize at various temperatures, the blue polymeric compound was always contaminated with an unidentified green sutetance. However, when the dry solid was allowed to polymerize at temperatures below 130 °C only the blue material was formed. 3... 

Lack of termination in a polymerization process has another important consequence. Propagation is represented by the reaction Pn+M -> Pn+1 and the principle of microscopic reversibility demands that the reverse reaction should also proceed, i.e., Pn+1 -> Pn+M. Since there is no termination, the system must eventually attain an equilibrium state in which the equilibrium concentration of the monomer is given by the equation Pn- -M Pn+1 Hence the equilibrium constant, and all other thermodynamic functions characterizing the system monomer-polymer, are determined by simple measurements of the equilibrium concentration of monomer at various temperatures. 

Et2 All coinitiators and MeCl, MeBr and Mel solvents at various temperatures. The H20 /EtAiei2/n-pentane system was also briefly investigated. A large number of comparative molecular weight and conversion data were gathered. The effect of MeX on the polymerization was investigated in detail. In this section, conversion and initiator efficiency data will be discussed. 

Similarly, Garcia-Rubio and Hamielec (17) conducted bulk polymerizations of acrylonitrile at various temperatures and initiator levels in glass ampoules. Their plots of the rate of polymerization as a function of conversion are typical of the extensive radical occlusion in this very glassy polymer. 

Figure 5.4 Effect of gas flow rate on (a) the SSP reaction rate of PET at temperatures of 190 and 220 °C, and (b) the rate of increase of the intrinsic viscosity of PET at various temperatures [13]. Reprinted from Polymer, 39, Huang, B. and Walsh, J. J., Solid-phase polymerization mechanism of polyethylene tereph-thalate) affected by gas flow velocity and particle size, 6991-6999, Copyright (1998), with permission from Elsevier Science...

Table 2 Polymerization rates (in 10 L mol s ) of CROP of EtOx with different initiators at various temperatures - acetyl chloride (AcCl), acetyl bromide (AcBr), acetyl iodide (Acl), and 2-bromo-2-methylpropanoyl bromide (BrEB/B)...

Formation of polymeric peroxycarboxylic acids of variously grafted celluloses, such as 228 and 229, where the thick line represents the main cellulose strand, and assessment of their thermal stability by following their decomposition at various temperatures is based on iodometric determination of the peracids . 

Because of their lower level of crystallinity these copolymeis soften at lower temperatures than polyethylene. Table I compares the torsional stiffness at various temperatures of an 18% ethyl acrylate-82 % ethylene copolymer with that of a 21,000 molecular weight, 0.918 density polyethylene made by high pressure polymerization (Bakelite DYNH, Union Carbide Corp.). 

The polymerization kinetics of the bisbenzocyclobutene diketone monomer 14 (Fig. 10) were studied in the melt at various temperatures by infrared spectroscopy [48]. This technique has the advantage that it is relatively insensitive to the physical state of the system as it proceeds from monomer melt through the gel point and into the vitreous state. In addition, quantitative... 

Investigation of the polymerization of levoglucosan at various temperatures and pressures led to the conclusion that dimers, tetramers, hexamers, and octamers are formed. One preparation was shown to contain approximately 2% of a nondialyzable fraction.209... 

Finally, the data published by Gee (30) permit one to evaluate the sharpness of a transition involving floor temperature. Gee studied the temperature dependence of the viscosity of liquid sulfur and observed its sudden, steep increase at a critical temperature followed by its decrease at still higher temperatures. He developed the first, relatively complete theory of equilibrium polymerization of liquid sulfur (30) from which he estimated the chain length of the polymeric sulfur at various temperatures. His results have been recently confirmed by experimental measurements of magnetic susceptibility of the liquid sulphur (50) and its electron spin resonance (57). 

The change in the oxidation state of the vanadium ion has also been observed in the ESR spectra of the soluble V(acac)3/A1(C2H5)2C1 catalyst at various temperatures. At temperatures below —40 °C no ESR signal could be detected, which suggests that the vanadium ions exsist in the trivalent state. A broad ESR signal (AH 20 mT) apperared at g — 1.98 at temperatures above —30 °C, and its intensity increased with temperature to reach a constant value at 20 °C. Thus, these spectral data indicate that the vanadium species active for the living polymerization of propylene are in the trivalent state. 

Chung et al. (1999) measured ADR release from thermo-responsive micelles at various temperatures through the micelle LCST using LTV absorbance at 485 nm in a time-course. The results of the ADR release from the thermo responsive micelles can be referred to the discussion of thermo responsive polymeric micelles by Chung et al. (1999) in the section of pharmaceutical applications. 

At the co-deposition of nanocomposite components formation of M/SC particles proceeds simultaneously with formation of a dielectric matrix, and the relationship between these processes determines the nanocomposite structure. This problem has been in detail investigated for the case of M/SC nanoparticles formation in polymer matrices. Synthesis of nanocomposite films by simultaneous PVD of polytetrafluoroethylene (PTFE) and Au has been carried out in works [62-64], Polymer and metal were sputtered under action of Ar ions and then the obtained vapors were deposited on substrates (quartz, glass, silica, mica, etc.) at various temperatures. Here, it is necessary to note that polymer sputtering cannot be considered as only physical process PFTE polymer chains destruct under action of high-energy ions, and formed chemically active low-molecular fragments are then deposited and polymerized on a substrate surface. 

Figure 29 provides a comparison of the polymerization activities of Cp TiCl3 and Cp TiF3 at various temperatures and Al Ti ratios. At all temperatures investigated, the fluorinated compound is more active than the chlorinated one. Although an increase of the Al Ti ratio to 900 enhances the activity of Cp TiCT, the opposite is observed with Cp TiF3. The higher activity of the latter complex was found at a usefully low Al Ti ratio of 300. Table XIX provides a summary of the results. 

Fig. 29. Polymerization of styrene by Cp TiCl3 and Cp TiFj/MAO catalysts at various temperatures and Al/Ti ratios. Cp TiCl3 = 6.3 x 10 4 mol/liter Cp TiF3 = 6.3 x 10 5 mol/liter (24).

More recently Italian workers investigated some aspects of cationic anethole polymerizations. Thus Rattu and Secci (140) used aluminum chloride and titanium tetrachloride and Secci and Mameu (141) employed boron trifluoride as catalysts at various temperatures. The latter authors found boron (U. V. spectroscopy) in the polymer and proceeded to propose a rather controversial mechanism. Their hypothesis implies that a cocatalyst is not necessary for the polymerization and the polymerization proceeds as follows ... 

The idea of intramolecular hydride shift polymerization reappeared in 1956. Russian authors polymerized isobutene using AlEt -TiCl mixtures as catalyst 151). Polymerization was carried out at various temperatures (+75 to —25° C.) and low molecular weight (7,300—10,120) products were obtained. Peculiarly, it was postulated that this polyisobutene contained a methyl group every fourth carbon atom ... 

It also can be produced directly from natural gas, methane, and other aliphatic hydrocarbons, but this process yields mixtures of various oxygenated materials. Because both gaseous and liquid formaldehyde readily polymerize at room temperature, formaldehyde is not available in pure form. It is sold instead as a 37 percent solution in water, or in the polymeric form as paraformaldehyde [HO(CH20)nH], where n is between 8 and 50, or as trioxane (CH20)3. The greatest end use for formaldehyde is in the field of synthetic resins, either as a homopolymer or as a copolymer with phenol, urea, or melamine. It also is reacted with acetaldehyde to produce pentaerythritol [C(CH2OH)4], which finds use in polyester resins. Two smaller-volume uses are in urea-formaldehyde fertilizers and in hexamethylenetetramine, the latter being formed by condensation with ammonia. 

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