Simultaneous gelation

Surprisingly, truly simultaneous gelation resulted in a minimum in the physical properties (see Section 7.3.3). While truly simultaneous gelation 

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Experiments were centered around conditions that would result in simultaneous polymerization or simultaneous gelation of the two components. Reactions off center resulted in one reaction or the other proceeding faster. Thus a range of properties at or near simultaneous gelation could be systematically observed. The range of the initiator concentration was 0.18-0.46% (based on n-butyl acrylate). The epoxy was prereacted from one to eleven hours before the acrylate mix was added. 

In SIN formation, both timing and rates of polymerization to form the two networks are important. With an acrylate-epoxy system, it was found that simultaneous gelation produced materials with poorer properties than those formed by slightly mismatched polymerization rates (6). In another instance (7), polyurethane-poly(n-butyl methacrylate) SINs in which the acrylate was initiated photolytically at various times after the onset of polyurethane formation produced a series of materials, presumably with the same chemical composition, with an average particle size that decreased as the delay time to acrylic initiation increased. Damping properties of these materials changed systematically across the series. 

The intersection of the PMMA gelation plane with that of the phase separation sail-like surface, the curvilinear line A-B, represents the critical line along which simultaneous gelation of PMMA and phase separation of the PU from the PMMA exists. Reactions passing to the left of this curve will have the PMMA gel before phase separation, while reactions to the right of A-B will phase separate before gelation takes place. 

The only peak at 254.5 °C observed in the as-received nanoparticles, as shown in Figure 12.5(b), is due to the decomposition of the iron oxide-hydroxide (goethite, FeOOH as proved by theFT-IR spectra) [31,76]. Similar to the TGA observation, a higher decomposition temperature (308.0 °C) was observed in PPy formed with the aid of nanoparticles than that of pure PPy formed without them (298.4 °C). Whereas only one peak was observed in the pure PPy samples, two exothermic peaks were observed in the DTA curves of the nanocomposites. These were due to the decomposition of PPy at 307 °C and the possible phase transition of iron oxide at 480 °C, as reported for the Fc203/PPy nanocomposites fabricated by the simultaneous gelation and polymerization (sol-gel) method [77,78] respectively. As compared with no obvious phase transition in the pure iron oxide nanoparticles, the observed phase transition was due to the intermediate product of PPy [77,78]. 

The gelation plane of the polyurethane is illustrated in Fig. 6.4 see G2-MMA-PMMA. For completeness, the gelation plane Gj of the PMMA from Fig. 6.3 is also shown. The gelation plane G2 occurred after about 67 % conversion of the PU. The intersection of the two planes, G1-G2, illustrates the line of simultaneous gelation of the two polymers. Reactions passing to one side or the other of this line will have one polymer or the other gelling first. It must be noted that the line G1-G2 also intersects the line A-B of Fig. 6.3, not shown. The intersection of these two curves expresses the presence of a triple critical point, where both polymers simultaneously gel and phase separate. While this triple critical point represents the ideal SIN synthesis condition, it would not, in general, produce the best physical or mechanical properties. 

Although the morphology found by Kim et aL, Figure 6.4, is intuitively expected for a SIN, even having simultaneous gelation of both polymers does not necessarily guarantee molecular mixing or dual-phase continuity. 

R. E. Touhsaent, Simultaneous Interpenetrating Polymer Networks of Epoxy and Poly(n-butyl acrylate). Morphology and Mechanical Behavior, Diss. Abstr. Int. B, 3864 (1975). 35(8). Epoxy/P(n-BA) SINs. Simultaneous gelation. Mechanical behavior. Ph.D. thesis. 

Figure 13.22 Figure 13.21 redrawn, to illustrate the gelation planes of both poly(methyl methacrylate), Gu and polyurethane, G2. The intersection of the two planes denotes the line of simultaneous gelation. In reality, neither G, nor G2 are perfectly planar. 

Scientists investigated on optical inteferometric stmctures that can be applied in toxic gas sensors. The sensor head consists of PANi and nafion layers deposited on the face of the telecommunication optical fiber. Humidity sensors are useful for the detection of the relative humidity (RH) in various environments. Polymer composites and modified polymers with hydrophilic properties have been used in humidity sensor devices. Researchers prepared nanocomposite pallets of iron oxide and PPy for humidity and gas sensing by a simultaneous gelation and polymerization process. This resulted in the formation of a mixed iron oxide phase for... 

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