Polymers cross-linking effects

Measurement of modulus over an extensive temperature range offers more information than T alone (16). Typical modulus—temperature curves are shown in Figure 1. Assuming that the reference temperature is the transition temperature of the copolymer, then curve A of Figure 1 is that of a softer polymer and curve B is that of a harder polymer. Cross-linking of the polymer elevates and extends the mbbery plateau Htde effect on T is noted until extensive cross-linking has been introduced. In practice, cross-linking of methacryhc polymers is used to decrease thermoplasticity and solubihty and to increase residence. 

Santora BP, Gagne MR, Moloy KG, Radu NS. Porogen and cross-linking effects on the surface area, pore volume distribution, and morphology of macroporous polymers obtained by bulk polymerization. Macromolecules 2001 34 658-661. 

Intraparticle diffusion limits rates in triphase catalysis whenever the reaction is fast enough to prevent attaiment of an equilibrium distribution of reactant throughout the gel catalyst. Numerous experimental parameters affect intraparticle diffusion. If mass transfer is not rate-limiting, particle size effects on observed rates can be attributed entirely to intraparticle diffusion. Polymer % cross-linking (% CL), % ring substitution (% RS), swelling solvent, and the size of reactant molecule all can affect both intrinsic reactivity and intraparticle diffusion. Typical particle size effects on the... 

UV exposure (at k < 300 nm) of the AZ resist prior to plasma etching causes polymer cross-linking (167, 168) or decomposition (169) of the resist photosensitizer near the surface. Thus, a hardened shell or case is formed that permits a higher bake temperature without resist flow and also reduces the etch rate due to plasma exposure. Exposure to inert plasma (e.g., N2) causes similar effects (170), possibly because of ion and electron, as well as UV, bombardment of the resist surface. When F-containing discharges are used, fluorination of the resist surface occurs that strengthens the resist (because of the formation of C-F bonds) and minimizes reactivity (171). 

Cross-linking effects are more important in the plateau and terminal zones. For moderately cross-linked polymers, such as soft vulcanized rubbers, the equilibrium modulus is similar in magnitude to the entanglement network modulus before vulcanization. In some cases, however, the former modulus may be higher by as much as a factor of 2 than the latter one, thus... 

The stereoselectivity of cyclopropane ester formation could also be effected by using reagents supported on linear or cross-linked polymers. The most important effects were noted with chloromethylated polymers cross-linked with divinylbenzene. The role of hyperconjugation in determining the stereochemistry of nucleophilic cyclopropanation of electrophilic alkenes has been studied and predicted In terms of equation 57 the... 

Figure 2. Schematic representation of the effect of surfactant, heat, and electrolyte on polymer cross-linking by a hydrophobic mechanism.

Table IV. Effects of Polymer Cross-linking on Yield and Stereochemistry ...

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