Polymer-monomeric phase

Polymerisation in the polymer-monomeric phase is characterised by two main factors. First, the rate at which it proceeds as a consequence of the gel-effect, where by virtue of the sizeable loss of trausmitting and segmental mobility of macroradicals, control changes from the rate of chain termination to the rate of it s propagation. Thus the process of chaiu propagation and chain termination take place as two different results... 

Polymerization in the polymer-monomeric phase is characterized by two main conditions, First, it proceeds under a gel-effect condition, at which, by virtue of sizeable loss of transmission and segmental mobility of macroradical control on the rate of chain termination passes to the rate of its propagation. This means, that the acts of chain propagation and its termination take place as two different outcomes of the interaction of the active radical Rj (propagation of chain) or a frozen one, the so-called self-burial, in accordance with the terminology of Refs. [20, 21], that is, an inactive radical Rz (monomolecular chain termination). This can be represented by scheme (6.4) ... 

Equations (6.61 >-(6.70) describe the kinetics of the linear photoinitiated polymerization of methacrylates in optically thin layers up to high degrees of conversion in the three reactive zones, namely the liquid monomer-polymeric phase, in the kolid polymer-monomeric phase and at the boundary of the above-mentioned phase division, according to the conception about the microheterogeneity of system. 

Kinetic model of postpolymerization in the polymer-monomeric phase... 

The types of postpolymerization kinetic curves shown can be qualitatively explained using the conception of the three reactive zones proposed earlier. Up to the moment when the polymerizing system is in the liquid monomer-polymeric phase (MPPh), namely up to the moment of conversion = 0 5, only a weak post-effect is observed. MPPh is characterized by low concentration of free radicals with a short life time. A visible post-effect is observed in the autoacceleration stage Po > Py , that is, at the beginning of polymer-monomeric phase elimination and formation of the interface layer at the phase division boundary between MPPh and the polymer-monomeric phase PMPh, which are new reactive zones. In such reactive zones the translational and segmental mobilities of the macroradicals are sharply decreased and the life times are sharply increased. This explains the essential post-effect. 

Equations (7.40M7.43) thus obtained describe the non-stationary kinetics of methacrylate polymerization (postpolymerization) in the polymer-monomeric phase, taking into account the wide spectrum of characteristic times of the postpolymerization inside the micrograins in the polymer-monomeric phase. 

As we can see from the comparison, in all cases the calculated kinetic curves are in good agreement with the experimental ones at all time intervals. This means that the proposed kinetic model and the kinetic equation (7.40) are true for the postpolymerization process of methacrylates in the polymer-monomeric phase, taking into account monomolecular chain termination. 

Taking into consideration the average value of the parameter b=ki [Ms ]= t [Mol (1-Ps°), monomolecular chain termination rate constants ifc, have been calculated via the postpolymerization process in the polymer-monomeric phase of glycidylmethacrylate (co=3.0% and co=0.5% (by mass() and also of iso-butylmethacrylate (co=3.0% (by mass), 0=37.4 W/m ). Results are presented in Table 7.14. 

Another approach to preparing a stable reversed phase with fewer residual silanols is the use of polyfunctional silanes of the type R2SiX2. These react to form a polymeric stationary phase that shields the siloxane bonds and restricts access to residual silanols. Polymer phases have higher carbon loads and are typically more retentive than monomeric phases. However, they are more difficult to synthesize reproducibly and may exhibit batch-to-batch variability in their properties. They also exhibit poorer mass transfer kinetics and so provide poorer efficiency than monomeric phases. 

A polymeric surface structure can result in slower mass transfer of the analyte in the polymer coating compared with the more brush- or bristlelike bonding of monomeric phases and thereby lead to higher efficiencies with monomeric phases. However, Thurman and Mills [75] note that the trifunctional reagent yields a phase that is more stable to acid because the... 

The difficulties encountered in LLC can be overcome by the use of chemically bonded stationary phases or bonded-phases. Most bonded phases consist of organochlorosilanes or organoalkoxysilanes reacted with micro-particulate silica gel to form a stable siloxane bond. The conditions can be controlled to yield monomeric phases or polymeric phases. The former provides better efficiency because of rapid mass transfer of solute, whereas the polymeric phases provides higher sample capacity. BPC can be used in solvent gradient mode since the stationary phase is bonded and will not strip. Both normal-phase BPC (polar stationary, non-polar mobile) and reversed-phase BPC (non-polar stationary, polar mobile) can be performed. The latter is ideal for substances which are insoluble or sparingly soluble in water, but soluble in alcohols. Since many compounds exhibit this behaviour, reversed phase BPC accounts for about 60% of published applications. The main disadvantage of silica bonded phases is that the pH must be kept between 2 to 7.5. However, bonded phases with polymer bases (polystyrene-divinylbenzene) can be used in the pH range of 0 to 14. 

The indicated characteristic of the 3-D polymerization is a direct proof of the microheterogeneity of a process, of an active role of the liquid monomer-solid polymer interface layer and also proof of the fluctuative mechanism of polymeric grain formation and propagation. This is reflected, first of all, in the kinetic constant the numerical value of which depends on the ratio of fractal characteristics of the surface and volume of the clusters of the solid polymeric phase into the liquid monomeric phase and liquid monomer into the solid polymeric matrix. Exactly that is why the calculations of IVo according to stationary kinetic equation (4.46) cannot take into account the individual character of the postpolymerization curves. 

It has been taken into account in the derivation of equation (5.1) from equation (5.6), according to experimental data, that at the earlier stage of bulk polymerization (at P=0.01) the monomeric phase becomes saturated as a relatively new polymeric phase, but the saturation level is low. That is why a concentration of monomer [My] in a saturated monomer/polymer solution is constant and, practically, equal to the eoncentration at the start of the polymerization, i.e., [My]=[Moj. In contrast, the volumetric part of the liquid phase (py) has a variable value and is changed via polymerization conversion as [Pg.173]

Another type of synthetic polymer-based chiral stationary phase is formed when chiral catalyst are used to initiate the polymerisation. In the case of poly(methyl methacrylate) polymers, introduced by Okamoto, the chiraUty of the polymer arises from the heUcity of the polymer and not from any inherent chirahty of the individual monomeric subunits (109). Columns of this type (eg, Chiralpak OT) are available from Chiral Technologies, Inc., or J. T. Baker Inc. 

Fig. 30. DSC traces showing the phase transition of the model membrane in its monomeric and polymeric form. Note the difference in the enthalpies of the transition monomer AH = 56 J/g, polymer AH = 26 J/g...

The DSC spectra confirm that the fluid phase of the polymerized vesicles remains and the phase transitions are retained with the introduction of the spacer group. As can been seen in Figure 8 of the DSC spectrum of the monomeric lipid, there is a peak around 28°C which corresponds to the phase transition of monomeric lipid. As the result of the presence of the spacer group, a similar phase transition can also be observed clearly in the spectrum of the polymerized lipid as shown in Figure 9, but the transition temperature is increased to 36°C by the presence of the polymer chains. 

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