Gel-fraction yield

The numerical value of coefficient b (32cm ) is in satisfactory agreement with the value of the so called integral absorption coefficient, as was estimated in independent experiment. An examination of the influence of the initial molecular weight on gel fraction yield showed the reciprocal relation between these two parameters. 

Also, the influence of the temperature of exposure (for a fixed radiation dose) on gel fraction yield, was tested. The relation studied is described by the equation ... 

Fig. 12 (a) Free-radical crosslinking copolymeiization of acrylamide and IV.iV -methylenefbis) acrylamide, (b, c) Gel-fraction yield plotted against reaction time for the case of conventional freezing (b) and low-temperature quenching (c). Gelation temperatures are indicated. (Plotted based on the data from [23])... 

Figure 13 shows the temperature dependence of the gel-fraction yield during the formation of chitosan-based cryogels, when this polyaminosaccharide was crosslinked with various amoimts of glutaraldehyde (for the reaction scheme see Fig. 7a). The results reveal that, in the moderately frozen aqueous medium, the highest performance of the crossUnking process was achieved in the vicinity of —25 °C, whereas above and below this temperature the gel-fracti(Mi yield was lower [10].

Fig. 13 Gel-fraction yield plotted against temperature for chitosan cryogels crosslinked using glutaraldehyde. Polymer concentration in the initial solution was 1.6 wt%. NH2-to-CHO molar ratio was 2.5 1 (curve 1), 15 1 (curve 2) and 25 1 (curve 3). (From [10] with permission from Springer)...

Fig. 15 Temperature dependence of the gel-fraction yield during the preparation of poly(styrene) gels (circles) and cryogels (squares) in nitrobenzene using 4,4 -xylylene dichloride as a crosslinker. The temperature scale is the relative temperature AT (as explained in Sect. 1). Polymer and crosslinker concentrations in the initial nitrobenzene solution were 0.3 M and 9.1 mol%, respectively (both with respect to the styrene units). (Plotted based on the data from [27])...

All these favorable and unfavorable factors and mechanisms are effective to a different extent during cryotropic gelation in both aqueous and organic media. For instance. Fig. 15 shows the bell-like temperature dependence of the gel-fraction yield when poly(styrene) was crosslinked with 4,4 -xylylene dichloride in nitrobenzene (see Fig.Sa for the reaction scheme). At temperatures 30-40 °C lower than room temperature, the efficiency of polymer crossUnking is higher than in unfrozen solutions (curve with open circles in Fig. 15) [27]. Thus, close similarity in the character of such temperature dependences for the processes in frozen aqueous and... 

Cellulose derivative Molar mass (g/mol) Gel fraction yield" (%) Degree of swelling... 

F. 4 Gel fraction yield of cryogels prepared fiom HECs of different molar masses at different polymer eoneentrations. Cryogels were obtained at a freezing temperature of —20 °C,... 

Fig. 5 Gel fraction yield of HEC cryogels obtained at various negative temperatures. Cryogels were prepared at initial polymer concentration...

Fig. 6 Gel fraction yield of HEC cryogels prepared with different photoinitiators. Cryogels were prepared at a freezing temperature of —20 °C, initial polymer concentration 1 mass%, polymer molar mass 1,300,000 g/mol, 2 mass% initiator, irradiation time 2 min...

Monomer Monomer concentration Irradiation time Gel fraction yield... 

FIGURE 17 Dependence of gel fraction yields on the time during hardening of block-copolymer at 160°C without accelerator (1), with iso-MTHP (3), with HMTA (5) and at 180°C without accelerator (2), with iso MTHP (4), with HMTA (6). 

Figure 17.20 Effect of irradiation dose and organoclay loading on the gel fraction yield of EVA/NR blends and the nanocomposites.

In the case of EVA/natural rubber/organoclay nanocomposites, at irradiation doses of 50, 100 and 150 kGy the gel fraction yield has been significantly reduced with the increment of organoclay loading, as shown in Figure 17.20. 

The natural rubber and EVA radicals can be scavenged by organoclay. Thus radical-radical interaction to form crosslink networks will be hindered by organoclay. In addition, exfoliation and intercalation of organoclay nanoparticles also block the sites for crosslinking in the polymeric matrix. However, at 200 kGy the gel fraction yield was not much alfected by organoclay loading. ... 

At the same time, crosslinking induced by free radicals will also be reduced due to the barrier effect. However, as the irradiation dose increases, more free radicals will be formed. The large amount of free radicals can overcome the barrier effect caused by well dispersed clay. This has been proved by the gel fraction yield. At lower irradiation doses the gel fraction is significantly reduced for the nanocomposites, whereas at 200 kGy the gel fraction for all the nanocomposites is almost the same as that for the pristine blend. 

Formation of a gel fraction has been detected on exposure of polyurethane films to NO2 [21]. Degradation of macromolecules simultaneously takes place in the sol fraction of the samples. The changes in the destruction degree and the gel-fraction yield with time are... 

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