Gelation behaviors

Fig. 8. Gelation behavior of alumina sols prepared from hydrolysis of aluminum isopropoxide at ( ) 90°C and (-) room temperature (49).

John, G., Jung, J.-H., Masuda, M. and Shimizu, T. (2004) Unsaturation effect on gelation behavior of aryl glycolipids. Langmuir, 20 (6), 2060-2065. 

In our previous article (14) the gelation in the polymerization of diallyl aromatic dicarboxylates has been experimentally examined in detail and discussed according to Gordon s theory (15). The discrepancy between actual and theoretical gel point conversion was quite large. In this connection, the gelation behavior of glycol bis(allyl phthalate)s was explored in detail from both experimental and theoretical standpoints. 

As already mentioned, McKenna (7), Frissell (4) and Greenhoe (6) have characterized the gelation behavior of different plastisols by the temperature at which the film breaks on hot peeling from the metal surface. We found, however, that the temperature at which the film could be peeled from the foil varied depending on whether the peeling was carried out before or after the film had been allowed to cool (Figure 5). We do not consider that this type of transition point has any particular practical significance. 

To keep the mathematics as simple as possible, here we sketch the arguments of Ziff [54] and Ziff and Stell [28], who carefully analyzed the post-gelation behavior of model 1. Ziff and Stell distinguish three versions of its post-gel behavior. 

Of interest also are the results of applications of the Smoluchowski equation for systems with more complex aggregation physics than that provided by bilinear kernels. Leyvraz and Tschudi [32] conjectured that for the kernel ICy-fi) ) gelation occurs only when co > 1/2. The post-gelation behavior of a general system with a multiplicative kernel given by Eq. (60) has been analyzed by van Don-gen et al. [56]. By assuming that the distribution past the gel point could be expressed through that at t=tc, thus... 

The statistical structural model for the gelation behavior of cyanate-epoxide polyreactions was described by Bauer [69] using the cascade formalism, according to the approach by Dusek [70], which had been previously applied for the polycyclotri-merization of acetylene derivatives. 

Bhattacharya etal. [73] reported gelation behavior of several L-phenylalanine-based amphiphiles. To explore the impact of molecular structures on gelation of L-phenylalanine derivatives, Bhattacharya and co-workers synthesized as many as twelve L-phenylalanine-based mono- and bi-polar derivatives and solubilized each of these in selected solvents. The formation of gel was found to depend on the concentration of the gelling agent, solvents and the temperature. The SEM and TEM studies suggested the formation of intertwined threads and fibers juxtaposed by slender filaments, which also produced a network with pores, which probably held the solvent molecules due to surface tension in the gel. 

Comparison of Gelation Behavior in Allyl and Vinyl Polymerizations... 

A similar solvent effect was also observed in the gelation behavior of the copolymerization of MMA with nonaethylene glycol dimethacrylate [104] The delay between the actual gel point and the theoretical one was much larger in... 

Yang, Y.-P. and Sigmund, W., Effect of particle volume fraction on the gelation behavior of the temperature induced forming (TIE) aqueous alumina suspensions, J. Am. Ceram. Soc., 84, 2138, 2001. 

ATRP was applied to the copolymerization of a monovinyl monomer and a divinyl cross-linker to study the experimental gelation behavior. The fundamental features of ATRP, including fast initiation and reversible deactivation reactions, resulted in a retarded gelation and the formation of a more homogeneous network in the ATRP process compared to gel formation in a conventional radical polymerization. The experimental gel point based on the monomer conversion in the ATRP reaction occurred later than the calculated value based on Flory-Stockmayer s mean-field theory, which was mainly ascribed to intramolecular cyclization reactions. The dependence of the experimental gel points on several parameters was systematically studied, including the ratio of cross-linker to initiator, the concentration of reagents, reactivity of vinyl groups, initiation efficiency of initiators, and polydispersity of primaiy chains. 

Scheme 1. Comparison of different gelation behaviors in conventional RP and...

Atom transfer radical polymerization (ATRP) was selected as an exemplary CRP technique to systematically study the kinetics and gelation behavior during the concurrent copolymerization of monovinyl monomers and divinyl cross-linkers (Scheme 2). The effect of different parameters on the experimental gelation was studied, including the initial molar ratio of cross-linker to initiator, the concentrations of reagents, the reactivity of vinyl groups present in the cross-linker, the efficiency of initiation, and the polydispersity of primary chains. Experimental gel points based on the conversions of monomer and/or cross-linker at the moment of gelation, were determined and compared with each other in order to understand the influence of each parameter on the experimental gel points. 

---