Monomer concentration, absorbance

Keeping the composition of copolymerization media constant the total comonomer concentration of which is varied. The absorbed dose was kept constant at 0.14 KGy for the AM-AANa and at 0.35 KGy for the AM-DAEA-HCl systems. The results are shown in Figs. 4 and 5, which show the rate of polymerization, Rp, the degree of polymerization, and the intrinsic viscosity increase with increasing monomer concentration. At comonomer concentration >2.1 M/L, DPn decreases with increasing comonomer concentration. From the logarithmic plots, exponents of the comonomer concentration for the AM-AANa system were determined to be [17,54]. 

The radiation sensitivity of a substrate is measured in terms of its GR value or free radical yield, which is the number of free radicals formed per 100 eV energy absorbed per gram. The highest grafting yields will occur for polymer monomer combinations in which the free radical yield of the polymer is much greater than for the monomer. It also follows that the grafting yield will increase at a lower monomer concentration. 

The kernel (26) and the absorbing probability (27) are controlled by the rate constants of the elementary reactions of chain propagation kap and monomer concentrations Ma(x) at the moment r. These latter are obtainable by solving the set of kinetic equations describing in terms of the ideal kinetic model the alteration with time of concentrations of monomers Ma and reactive centers Ra. 

Here kf and kb do not have solely their usual meanings as forward and backward chemical rate constants, because the free monomer concentration has been included as a factor in kf and the concentrations of the byproducts of the forward reaction (inorganic pyrophosphate and water) have been absorbed into kb. Since there are actually four different types of monomer, each template site specifying, according to the Watson-Crick base-pairing rules, which type is to be incorporated at that site, this use of the same kf for each step is strictly valid only if all four monomer concentrations are equal, as well as essentially invariant during the duration of the process, and if the true rate constant for the incorporation of each type of monomer is independent not only of the nature of the monomer to be added but also of the nature of the sequence already incorporated. 

Photooxidation of Eosin with periodate ion has been used to initiate the polymerization of acrylonitrile in aqueous solution [187]. Addition of acrylonitrile to a periodate solution shifts the absorption maximum from 220 to 280 nm. This spectral change is interpreted as being due to complex formation between the monomer and oxidizing agent. The rate of photopolymerization increases linearly with the absorbed light intensity and monomer concentration. The observed intensity dependence indicates the main chain terminator is not produced photochemically. Polymer is not formed when the concentration of periodate ion is lower than 0.5 mM and the rate of polymerization is independent of its concentration for higher values. 

The patent and open literature were searched for examples of dye sensitized photopolymerization in which a common monomer (acrylamide), and one of several common dyes (thionine, T methylene blue, MB or rose bengal, RB) were used in combination with a stated concentration of an activator. The polymerization conditions (monomer concentration, light intensity absorbed, and extent conversion) were stated in each case chosen for inclusion. The relative photospeed of the system was calculated based on several corrections to the raw data. We here define the relative photospeed of a composition as the inverse of the exposure time t needed to effect some fixed percentage of monomer conversion. 

Shape of the Polymerization Curves. Since polymerization takes place within the polymer particle, the rate depends on monomer concentration in the particles this concentration remains relatively constant as long as free monomer phase is present. At some point during the polymerization, the amount of polymer present is sufficient to absorb essentially all of the unreacted monomer. After this point in the polymerization, the monomer consumed by the radicals cannot be replaced and monomer concentration in the particle must decrease. It then follows that the rate must also decrease. 

The presence of a hydrophobic-hydrophilic interface can dramatically change the reaction conditions. The hydrophobic core will selectively absorb hydrophobic species from the solution (Fig. 12), and this will result in a redistribution of monomer concentrations between the core and bulk solution. Because the probability of attachment for each comonomer is determined by its concentration in a relatively small reaction volume near an active chain end, the active center inside the hydrophobic core will mainly attach more hydrophobic species on the other hand, when the active center is located on the globule surface, it will mainly attach polar (soluble) monomers. In this way, the two-layer globule will grow, retaining its core-shell structure with a predominantly hydrophobic core and a hydrophilic outer envelope (see Fig. 12). 

The major process for poly(vinyl chloride) production is the suspension system. Typical reaction temperatures are 50-65 C. As the reaction proceeds, a conversion ( 76%) is reached at which the only monomer left in the system is that absorbed in the polymer particles. This occurs when the monomer concentration is about 30 wt % in the particles. The occurrence of this phenomenon is signaled by a drop in the reactor pressure. Normal pressures in the autoclaves are initially about 150 psig (pounds per square inch, gauge), and it is usual to carry out polymerizations until the pressure drops to about 20-70 psig, depending on the reaction temperature. Water may be injected into the reaction vessel as the polymerization proceeds, to compensate for the volumetric contraction between monomer and polymer. This also helps prevent the reaction mixture from becoming too viscous. As well, the water addition enhances the cooling capacity of the reactor because it increases the heat transfer area on the walls. 

In solvents of high dielectric constant, (e.g. dimethylformamide), formaldehyde polymerized sluggishly and polymers were formed in low yield. In similar solvents, aliphatic aldehydes could not be polymerized. Precipitated aldehyde polymers have the tendency to absorb monomers. The monomer concentration near the propagating site may be much hi er than that in the surrounding solution. This occurs with n-butyraldehyde polymerizations in pentane [5] the polymer precipitated during the polymerization is highly swollen by the monomer. 

Figure 6. Dependence of the absorbance ratio DmS/D, cc on monomer concentration in the cyclopolymerization of methacrylic anhydride in benzonitrile. Key ...

By comparing the relative rate of uptake of two different lipid probe molecules, another piece of evidence for a monomeric mechanism in lipid uptake by membranes has been found. Hoffman [70] and Hoffman and Yeoh [71] have determined the relationship between micellar concentration and uptake by rat small intestine in vitro for oleic acid and a monoglyceride analog, a 1-monoether. They found that the rate of uptake for both of the two micellar solutes was linearly dependent on the micellar concentration, but that the ratio of rate of uptake was different from the molar ratio of the two lipids in the micellar phase. Oleic acid was absorbed more rapidly than the monoether, probably due to a higher monomer concentration in the... 

Nonylphenyl methacrylate was synthesized as a UV-absorbing monomer to confirm the effect of this type of hydrophobic monomer on the surfactant solution. Results are shown in Figure 5 (the monomer concentration has been adjusted on the basis of the number of double bonds obtained from the NMR results see the Experimental Details section). Although the points are in an almost straight line, the intercept of a least-squares line through all of the points would be about 5000 however, the intercept must be zero. Therefore, there must be an initial linear relationship that includes the origin. At higher nonylphenyl methacrylate concentrations, the MW is lower than extrapolated from the initial line. Thus, this hydrophobic monomer also acts as a cosurfactant. 

Direct measurement of absorbance of different functional groups, measurement of end groups, analysis of specific interactions and monomer concentration can all be used to monitor quantitative copolymer composition. Copolymer composition is determined by using the absorbance intensity ratio of monomer specific vibrational modes of vibration. A number of copolymer systems have been investigated ... 

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