Fraction polymerized material

If the nucleated assembly is self-catalyzed, then this modifies only the role of the equilibrium constant K in the non-self-catalyzed model and has to be replaced by the ratio K/Ka. This means that we again obtain for the fraction polymerized material f=KaNa/(1 + KaNa) but that the degree of polymerization averaged over the active material only now obeys (Ciferri, 2005)... 

For small Ka -C 1, the fraction polymerized material can in the vicinity of the polymerization temperature be described by the approximate expression (Jonkheijm et al., 2006)... 

Figure 7 The fraction polymerized material fas a function of the dimensionless time Ty according the kinetic Landau model discussed in the main text, with h the nucleation rate. Shown are results valid in the limit where the nucleation reaction is rate limiting, for a quench to X/Xp = 2 where in equilibrium f— 0.5. Depolymerization is much faster than polymerization.

Figure 5 Universal polymerization curve of EPs. Plotted is the fraction polymerized material r/ as function of the concentration ratio / p, where is the concentration at the half-way or polymerization point. The line... 

Figures Universal polymerization curve of EPs. Plotted is the fraction polymerized material as a function of the dimensionless ratio hp T - Tp)/kBT with hp the net enthalpy gain of the formation of a single link, Tp the concentration-dependent polymerization temperature, and kg Boltzmann s constant. The line gives the theoretical prediction of the isodesmic model. The symbols Indicate experimental data on five chemically different ollgo(phenylene vlnyl)s In the solvent methyl cyclohexane at a concentration of 1M [38], By fitting to the data, values of hp are obtained from 24 to 70 kg T equivalent to 60 to 170 kJ mol". ...

Figure 7 Polymerization curves of EPs as a function of the temperature T relative to the reference temperature Tp at the crossover from the monomer to the polymer-dominated regimes. Different curves give the fraction polymerized material rj for different values of the dimensionless link enthalpy hp/k Tp = 15, 30, 60, 90 (from bottom to top).

About 2 X 10 Ib/year of 1 2 epoxypropane is produced in the United States as an intermediate in the preparation of various polymeric materials including polyurethane plastics and foams and polyester resins A large fraction of the 1 2 epoxypropane is made from propene by way of its chlorohydrm... 

Chemicals responsible for odor in some PUR foams were synthesised by polymerisation of PO in CH2CI2 with Bp2(C2H )20 catalyst (114). The yield was 25% volatile material and 75% polymeric material. The 25% fraction consisted of dimethyldioxane isomers, dioxolane isomers, DPG, TPG, crown ethers, tetramers, pentamers, etc, and 2-ethy1-4,7-dimethyl-1,3,6-trioxacane (acetal of DPG and propionaldehyde). The latter compound is mainly responsible for the musty odor found in some PUR foams. This material is not formed under basic conditions but probably arises during the workup when acidic clays are used for catalyst removal. 

Thermosetting Reactive Polymers. Materials used as thermosetting polymers include reactive monomers such as urea—formaldehyde, phenoHcs, polyesters, epoxides, and vinyls, which form a polymerized material when mixed with a catalyst. The treated waste forms a sponge-like material which traps the soHd particles, but not the Hquid fraction the waste must usually be dried and placed in containers for disposal. Because the urea—formaldehyde catalysts are strongly acidic, urea-based materials are generally not suitable for metals that can leach in the untrapped Hquid fractions. Thermosetting processes have greater utiHty for radioactive materials and acid wastes. 

Distillation. Most fatty acids are distilled to produce high quaHty products having exceUent color and a low level of impurities. Distillation removes odor bodies and low boiling unsaponifiable material in a light ends or heads fraction, and higher boiling material such as polymerized material, triglycerides, color bodies, and heavy decomposition products are removed as a bottoms or pitch fraction. The middle fractions sometimes can be used as is, or they can be fractionated (separated) into relatively pure materials such as lauric, myristic, palmitic, and stearic acids. 

The sizes and concentration of the free-volume cells in a polyimide film can be measured by PALS. The positrons injected into polymeric material combine with electrons to form positroniums. The lifetime (nanoseconds) of the trapped positronium in the film is related to the free-volume radius (few angstroms) and the free-volume fraction in the polyimide can be calculated.136 This technique allows a calculation of the dielectric constant in good agreement with the experimental value.137 An interesting correlation was found between the lifetime of the positronium and the diffusion coefficient of gas in polyimide.138,139 High permeabilities are associated with high intensities and long lifetime for positron annihilation. 

Another possible explanation is that singlet O2 somehow leads to crosslinking. The reactions of O2 have been extensively studied (34), and do not appear relevant to these copolymers. The only functionality that could conceivably react with singlet O2 is a vinyl chain termination, which could produce a hydroperoxide that might then participate in crosslinking. However, in a study of free radical polymerized PMMA (35), the maximum fraction of polymer chains with vinyl ends was found to be 0.36, for bulk polymerized material in benzene solution the fraction was 0-3%. This result, plus the fact that the insolubilization occurs immediately during photolysis at room temperature, makes it very unlikely that such hydroperoxides are involved. 

In comparison, no structural modification of model B was seen before 120 h of aging (80 °C). However, after 120 h two small doublets appeared in the NMR spectrum and several additional peaks became noticeable in the NMR spectrum. It was determined by NMR and IR spectroscopy that the hydrolysis products were an imide/carboxylic acid and an imide/anhydride. Model B was then aged for 1200 h at 80 °C to quantitatively determine the amount of hydrolysis products as a function of time. The relative intensity of the peaks due to carboxylic acid is constant after some time. The authors suggest that an equilibrium occurs between model B and the products formed during hydrolysis, and therefore, the conversion to hydrolysis products is limited to about 12%. This critical fraction is probably enough to cause some degradation of polymeric materials, but research on six-membered polyimides has remained active. 

When AN powder is mixed with a polymeric material, the oxygen gas produced by the decomposition of the AN powder reacts with the hydrocarbon fragments of the thermally decomposed polymeric material. The major combustion products are GO2 and H2O. Nitropolymers are not used as fuel components of AN pyrolants because of the reaction between the NO2 formed by their decomposition and the AN powder. This reaction occurs very slowly and damages the physical structure of the AN pyrolant. Instead, polymeric materials containing relatively high mass fractions... 

Process in which a polymeric material, consisting of macromolecules differing in some characteristic affecting their solubility, is separated from solution into fractions by successively decreasing the solution power of the solvent, resulting in the repeated... 

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