Sol-gel analysis

In principle, detailed information about the radiation chemistry of a polymer may be obtained using sol-gel analysis as a function of dose to provide estimates of both crosslinks (x) and fractures (F) (5). Such estimates have been made in only one case for PET (18) but are supplemented by estimates made from other data obtained at high dose rates in Table II. The data used are scanty, generally only three points, and more detailed work is desirable. In addition, further work is required to... 

The formation of a polymer networks starts with an increase in molecular weight and formation of branched structures. At a typical extent of reaction, the gelation point is that point at which a network is first formed. The extent of reaction as well as the cross-linking density in radiation-induced cross-linking processes is determined by the radiation dose. The term dose means the quantity of radiation applied to or absorbed accidentally by a given volume or mass of sample. The absorbed dose is measured in Gray (Gy), 1 Gy = 1J kg-1. Therefore, the formation of a polymeric network needs a certain dose, the gelation dose Dg, which can be determined by sol-gel analysis. ... 

Typically, a cross-linked polymer is insoluble. During the cross-linking reaction, the amount of polymer chains being connected by chemical bonds increases. The determination of the insoluble fraction (gel) and the soluble fraction (sol) of a polymer is done by the sol-gel analysis. In general, the cross-linking density increases and the sol content decreases with increasing dose. But, it is necessary to determine these correlations for each polymer at the conditions during irradiation. 

Sol-gel analysis is an important tool for distinguishing between polymers that can be cross-linked by irradiation and polymers that are not cross-linkable by radiation techniques. These experiments are typically done for wall-to-wall gels and offer the possibility to determine the irradiation conditions for microgel formation. Charlesby and Pinner first obtained a simple expression relating the soluble part of a polymer sample, the sol fraction (5) or sol content (in contrast to the insoluble part, the gel fraction (g) or gel content) to the absorbed dose D of radiation [10, 12],... 

Fig. 9 Sol-gel analysis of PVP gel. (a) Gel content versus radiation dose (e-beam) (b) Charlesby-Pinner plot (with regression line).The gelation dose is determined to Dg = 94 kGy from the intercept follows po/ijo = 103. Reprinted from Burkert et al. (2007a), p. 1326. Copyright (2007), with permission from Elsevier...

With regard to the mechanical reactirai of a polymer network to a stress applied, it is important that loose ends of macromolecules in a network structure are as shmrt as possible and/or their concentration is low. As these ends mostly extend out of the lamellas of crystallites then, while crossUnking is taking place in an amorphous phase and with the simultaneous presence of crystallites, a network with small loose ends should be formed. The crosslink junctions stabilize the natural molecular network (entanglements and crystallites), and every chain in the system is potentially elastically operative and can contribute to the stress in a tensile experiment [33]. The stabilization effect of chemical crosslinks on entanglements and crystallites may be the direct cause of observed differences in the determination of the amount of chemical crosslinks from mechanical property measurements and sol-gel analysis of the cross-linked polymer. 

The identification of polymeric grains as microreactors, in which the polymerization process is localized from the moment of grain formation and until the moment of their contact and propagation into a microheterogeneous polymeric body, has been carried out by sol-gel analysis [122] and thermometrical methods [1231 in studies of oligoesteracrylates polymerization kinetics. 

Network strand Cross-link SEC Sol-gel analysis physico-chemistry... 

From sol-gel analysis (25) of Y ii i diated poly-(caprolactone) the ratio of chain scission to cross-linking was determined to be about 0.9, as compared with the corresponding value of 0.3-0.4 for polyethylene. 

Fig. 4 Sol-gel analysis of a photopolymerized nanocomposite hydrogel. The gel point is observed at an exposure time of 105 s (Reprinted with permission from Ferse et al. 2008. Copyright 2015 America Chemical Society)...

Polycyanurate network was modified with hydroxyl-terminated polyester, poly(butylene glycol adipate), PBGA, by polycyclotrimerization of bisphenol A dicyanate in the immediate presence of PBGA [18]. The modified networks with PBGA content from 5 to 20 wt. % were characterized by a combination of FTIR, DSC, TMA, TGA, impact testing and sol-gel analysis. It has been established that almost the whole PBGA was chemically incorporated into the PCN structure. It is supposed that the chemistry of such incorporation is the same as that shown in Figure 2. 

The best polymer film candidate based on sol/gel analysis performed as described, was dissolved (5 wt.%) in methyl-isobutyl ketone (MIBK) and spin coated onto a 4 silicon wafer at 2(X)0 rpm using hexamethyldisilazane (HMDS) as a primer. Small sections of the more homogenoeus wafers were sectioned and exposed to a IS keV electron beam using an electron beam/scanning electron microscope lithography tool. The E-beam exposure of the wafer was performed imder vacuum at 2 X 10 torr. Subsequent development was achieved in 10 seconds, again using THF as the solvent. 

The accepted model of a gel for purposes of sol-gel analysis or elasticity parameters is the ring-free infinite tree-like molecule. It is successful, even though such a molecule could not be packed into three-dimensional space after the gel point, i.e. when its relative conversion a/a shall denote this... 

Abad, L., San Diedo, C., Relieve, L., Aranilla, C., Dela Rosa, A. M., Janik, I. Rosiak, J. (1999). Sol-gel analysis of crosslinked polymers. Proceedings 1 Philippine Chemistry congress, Cebu City, PhiUppines, 466. 

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