Polymer-rich fraction

Fig. 3.8 Normal-phase-HPLC chromatograms of PA fractions generated by a combination of solvent extraction and column chromatography on Toyopearl resin (protocol 2). a monomer-rich, b ohgomer-rich, c dimer-rich, and d polymer-rich fractions. Compounds were detected with post-column derivatization using DMACA...

Fig. 3.10 Reverse-phase HPLC chromatogram of PA phloroglucinol cleavage products from the polymer-rich fraction of GSE...

Crude GSE can be separated into distinct components from monomer-rich to oligomer- and polymer-rich fractions by solvent extraction followed by chromatography on Toyopearl resin. The pre-fractionation of the tannin crude extract by liquid-liquid extraction with ethyl acetate fractionates the monomers into the organic phase and improves the subsequent fractionation of oligomers and polymers on Toyopearl HW 40 resin. This fractionation technique is easy to operate and... 

Figure 8.3b shows that phase separation in polymer mixtures results in two solution phases which are both dilute with respect to solute. Even the relatively more concentrated phase is only 10-20% by volume in polymer, while the more dilute phase is nearly pure solvent. The important thing to remember from both the theoretical and experimental curves of Fig. 8.3 is that both of the phases which separate contain some polymer. If it is the polymer-rich or precipitated phase that is subjected to further work-up, the method is called fractional precipitation. If the polymer-poor phase is the focus of attention, the method... 

Process in which a polymeric material, consisting of macromolecules differing in some characteristic affecting their solubility, is separated from a polymer-rich phase into fractions by successively increasing the solution power of the solvent, resulting in the repeated formation of a two phase system in which the more soluble components concentrate in the polymer-poor phase. 

The homopolymer of DMP dissolves readily in methylene chloride but precipitates on standing as a crystalline polymer-CH2Cl2 complex, providing a method for distinguishing between block copolymers and mixtures of homopolymers. Random copolymers prepared by methods a and b form stable solutions in methylene chloride. Copolymers with a 1 1 ratio of DMP and DPP prepared by methods c and d also yield stable methylene chloride solutions. Since the NMR spectrum shows that the DMP portion of these materials is present as a block and the solubility in methylene chloride shows that DMP homopolymer is absent, these copolymers have the block structure. They can be separated by crystallization from m-xylene into an insoluble DPP-rich fraction and a soluble DMP-rich fraction, both fractions having the NMR spectra characteristic of block copolymers. A typical 1 1 copolymer prepared by adding DMP to growing DPP polymer yielded 35% of insoluble material... 

The portion of drug that remains trapped within the polymer may be estimated by measurfggf he the polymer-rich phase. In instances whl ef polymer-rich phase issimilartothatof neat polymer, a complete phase separation may be assumed. In other instances, the differ gsolid solubility of drug in polymer. As shown in Figure 18.12, phase separation of trehalose was observed from dextran solid dispersions in the 4-day and 34-day samples. However, a certain fraction of trehalose remained miscible with dextran as indicated by the substantially low... 

As we will see, some anomalies in the isotopic composition of carbon, hydrogen and oxygen can be explained on the basis of this assumption, and we will start the discussion with the deuterium-rich matter in carbonaceous chondrites. This deuterium-rich matter is essentially present as complex macromolecules 70 73 96 97). The carbon in these samples is essentially normal 76,98). For some polymer-type fractions, the deuterium content is up to 32 times higher than the galactic value (D/H 2 x 10s in the number of atoms per cubic centimeter). High deuterium enrichments are known in interstellar molecules and the mechanism of this enrichment is fully understood. For an excellent review dealing with interstellar chemistry, see the paper by Winnewisser 99) and the previously mentioned book by Duley and Williams 13). 

The results showed that all batch polymerizations gave a two-peaked copolymer compositional distribution, a butyl acrylate-rich fraction, which varied according to the monomer ratio, and polyvinyl acetate. All starved semi-continuous polymerizations gave a single-peaked copolymer compositional distribution which corresponded to the monomer ratio. The latex particle sizes and type and concentration of surface groups were correlated with the conditions of polymerization. The stability of the latex to added electrolyte showed that particles were stabilized by both electrostatic and steric stabilization with the steric stabilization groups provided by surface hydrolysis of vinyl acetate units in the polymer chain. The extent of this surface hydrolysis was greater for the starved semi-continuous sample than for the batch sample. 

In mechanistic models these interactions can be directly simulated. Thus the issue of kinetic coupling (molecular interactions) may well be somewhat artificial and only introduced by analysis at the less detailed molecular or global levels. Likewise, the intrusions of diffusion may also be somewhat artificial and a result of modelling at the molecular or global level. That is, mechanistic simulations can now account for the movement as well as reaction of molecules and active centers (54). This becomes especially convenient when the device of a percolation lattice is used. Molecules can then be assembled, moved and reacted on the lattice which, in addition to allowing for simulation of the mechanism of diffusion in reaction, can also provide information about global product fractions, such as polymer gel fraction and cross-link density. The literature of polymer science is rich in these types of applications. 

Summing up, the two-phase model is physically consistent and may be applied for designing industrial systems, as demonstrated in recent studies [10, 11], Modeling the diffusion-controlled reactions in the polymer-rich phase becomes the most critical issue. The use of free-volume theory proposed by Xie et al. [6] has found a large consensus. We recall that the free volume designates the fraction of the free space between the molecules available for diffusion. Expressions of the rate constants for the initiation efficiency, dissociation and propagation are presented in Table 13.3, together with the equations of the free-volume model. 

A chemist dissolved a 50-g sample of a polymer in a solvent. He added nonsolvent gradually and precipitated out successive polymer-rich phases, which he separated and freed of solvent. Each such specimen (which is called a fraction) was weighted, and its number average molecular weight was determined by suitable methods. His results follow ... 

If the volumes of the polymer rich and solvent-rich phases are V and V, respectively, then the fraction /, of t-mer that remains in the solvent-rich phases is given by... 

Figure 9.2 Schematic phase diagram of a polymer/solvent mixture, where y is the Flory chi parameter, and xe = 1/2 is x at the theta temperature. The quantity Xe X along the ordinate is a reduced temperature, and is the polymer volume fraction. CP is the critical point, and BL is the binodal line. SSL and KSL are the static symmetry line and the kinetic symmetry line, respectively. These lines define the phase-inversion boundaries during quenches. In quenches that end at the right of such a line, the polymer-rich phase is the continuous phase, while to the left of the line the solvent-rich phase is the continuous one. SSL applies at long times, after viscoelastic stresses have relaxed, while KSL applies at shorter times before relaxation of viscoelas-...

Another substrate hydrolyzed by thermal polyanhydroamino acids is p-nitrophenyl phosphate (NPP). Oshima 25) has tested acidic proteinoids, a histidine-rich proteinoid, and proteinoids that contain a relatively high proportion of basic and neutral amino acids (p. 377). These polymers were fractionated in water and aqueous alkali, and by molecular sieve chromatography. Soluble fractions were used in most experiments on catalysis. The possibility of microbial contamination was obviated indirectly by virtue of several circumstances. These included using fractions with molecular weights between 2500 and 4000, and adding toluene to the test reaction mixtures. The reactions were carried out at 30° in 0.03 M tris buffer, pH 7.6, in the presence of 1 pmole/ml of NPP and 0.03-1.5 mg/ml of thermal polymer pM ZnCU and IQfiM MgCl2 were also present in the solutions. Truly catalytic... 

The wet, coagulated membrane gel Is usually dipped Into a nonsolvent bath. Desolvatlon followed by partial replacement with nonsolvent and shrinkage of the gel occur. After being dipped, the membrane Is dried. The volume fraction polymer concentration In the polymer-rich phase Is given as V. The unit volume of a polymer particle decreases to V(p /p ) after drying. Here, p and p are the densities of the p y er-rich phase and of polymer respectively.. The radius of the polymer particle S. changes to S (=S2(VPg/p ) O by drying. 

Several variations of this process have been described. By the addition of NMP, the reaction mixture separates into a more dense polymer-rich liquid phase, and into a less dense phase, containing the oligomers, and unreacted reactants. The less dense phase can be used for further recovery of a high molecular fraction or reuse in a further polymerization step. ... 

Centrifugal fractionation of the cell-free system showed that the enzymes which caused incorporation of glucose could be separated from the sulphate-rich material and would add glucose to the sulphate-poor component more efficiently in its absence. On re-addition of the sulphate-rich fraction, incorporation into the sulphate-poor components was slowed and some addition of glucose to sulphate-rich material could be shown. These results clearly suggest competition for a common precursor, but do not necessarily show the involvement of a single or common glycosyltransferase system, or a close relation between the two types of polymer. 

Phase Separation. All experimental work concerning PSLC s suggests, more or less strongly, that phase separation of a polymer-rich phase occurs upon polymerization. Such polymerization-induced phase separation may be expected, since the total mole fraction of monomer and polymer molecules, and therefore also the entropy of mixing, decreases dramatically upon polymerization. There are changes in the enthalpy of mixing, also as a result of reaction, as the acrylate moiety is converted to its saturated counterpart. 

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