Gelation condensation polymerization

Falling off of the log viscosity-time cure curve can also occur due to dewetting, or wall slip, at the cone-sample interface. This occurs rarely, in our experience, and probably more with highly filled samples as gelation is approached. A kinetic order greater than unity could also produce a curvature similar to C, but evidence of such kinetic orders for condensation polymerization reactions has not been reported from chemorheological studies, to our knowledge. (Certain types of addition polymerization reactions may show non-first-order viscosity kinetics.)(13)... 

The percolation transition can be described in space of any dimension. Examples of two-dimensional percolation are deluge, forest fire, spreading of a contagious disease in an orchard, and gelation of a polymer at an air-water interface. Examples of three-dimensional percolation are substitutional alloys and bulk polymer gelation. A problem analogous to one-dimensional percolation is the condensation polymerization of bifunctional monomers described in Section 1.6.2. 

Another reaction that does not lead to gelation is the polymerization of hyperbranched polymers from ABy, monomers (each with a single functional group of type A and/— 1 functional groups of type B) in which A can only react with B. For functionality f=2, this reduces to the condensation polymerization of linear chains, described above. For... 

Condensation polymerization can be used to produce graft copolymers. However, like the other techniques, it suffers from self-condensation of the backbone, ring formation, and cyclization, which ultimately leads to gelation. 

Finally, the acid- or base-catalyzed reaction of hydrolysis and condensation polymerization of TEOS into a layered silicate gallery could affect the physical properties of silica-pillared magadiite and kenyaite. The samples that were silica-pillared by acid- and base-catalyzed reactions show a large increase in basal spacing. Also, they exhibit relatively narrow pore size distributions and show high surface areas, depending on the type of catalyst and layered silicate. These results indicate that variations in the conditions of gelation contribute to the improvement in the physical properties of silica-pillared molecular sieves. 

Set, V—To convert an adhesive into a fixed or hardened state by chemical or physical action, such as condensation, polymerization, oxidation, vulcanization, gelation, hydration, or evaporation of volatile constituents. The term is most commonly used with thermoplastic adhesives, unless a chemical process, such as polymerization, is involved. 

Because the average cluster size is proportional to M2it)/Mi(t), the gelation takes place at the time f, at which M2(t) becomes infinite. When the bonding probability Ky is constant, i -I- j, or ij (Table 2), the Smoluchowski equation can be solved analytically [15]. In particular, it will yield results similar to those with the FS model at Ky = ij. In the /-functional condensation polymerization system (FS model), the functionality /(/ — 2) -I- 2 of the cluster with degree of poljnnerization i is proportional to the volume. However, if the shape of the cluster (branched... 

Hydrolysis and Polycondensation. As shown in Figure 1, at gel time (step C), events related to the growth of polymeric chains and interaction between coUoids slow down considerably and the stmcture of the material is frozen. Post-gelation treatments, ie, steps D—G (aging, drying, stabilization, and densification), alter the stmcture of the original gel but the resultant stmctures aU depend on the initial stmcture. Relative rates, of hydrolysis, (eq. 2), and condensation, (eq. 3), determine the stmcture of the gel. Many factors influence the kinetics of hydrolysis and... 

The insolubilization of cations and anions during the setting and hardening process is thus paralleled by that of silica. Under add conditions orthosilicic add condenses first to form polymeric silidc add and then silica gel (Her, 1979 Andersson, Dent Glasser Smith, 1982). These processes are discussed more fully in Section 6.5.4. Gelation of silica, like the formation of salt gels, is enhanced by a reduction in the acidity of solutions. 

A polymerization that provides a transition into a discussion of gelation is the condensation of an excess of A-B with a small amount of an /-functional monomer, R-A/, that contains / equivalent functional groups of Type A, but no functional groups of Type B.[3 Linear chains are obtained when / is 1 or 2, but multichain condensation polymers are produced when/>2. At high conversion the polydispersity index depends only on/. 

Isobutene was condensed at —78°C into a graduated cylinder under nitrogen, and 12 ml were transferred into a reaction vessel containing 1 g of tri-n-octylaluminum. The mixture was stirred for 30 minutes at —78°C and then transferred to a second reaction vessel. It was then treated with 48 rml of 0.05M l,2-bis(9-bora-l,2,3,4,5,6,7,8-octafluorofluorenyl)-3,4,5,6-tetrafluorobenzene dissolved in toluene, which resulted in an uncontrolled, exothermic polymerization accompanied by rapid gelation of the solution. The mixture was quenched with 1 ml of 0.2M NaOCHs in methanol. The volatiles were removed and the residue washed with methanol then dissolved in hexane. The solution was filtered, concentrated, and the product isolated. Reaction scoping results are provided in Table 1. 

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