Pendant double bond

The reaction of ozone with olefinic compounds is very rapid. Substiments on the double bond, which donate electrons, increase the rate of reaction, while electron-withdrawing substituents slow the reaction down. Thus, the rate of reaction with ozone decreases as follows polyisoprene > polybutadiene > polychloroprene [48]. The effect of substiments on the double bond is clearly demonstrated in Tables 15.2 and 15.3. Rubbers that contain only pendant double bonds such as EPDM do not cleave since the double bond is not in the polymer backbone. 

The subscript 3 is used to designate the pendant double bonds. Therefore, the fundamental equation is given by ... 

Figure 3 The Effect of the Reactivity of Pendant Double Bonds on the Applicability of Equation 8.

Therefore, concentrations of the polyvinyl monomer, the branching and network formation proceeds as shown in Figure 12. Mlcrogel-llke species are formed first which are highly internally crossllnked. The pendant double bonds in the interior are very Immobile so that their reactivity is strongly diffusion controlled and they almost cannot react at all, even with the monomers. Only the more mobile pendant double bonds in the periphery of these species can enter into reactions with macroradicals and participate in Interbinding of the species together. 

The tendency toward cyclization decreases considerably (lower kjkp value) for unsym-metric 1,6-dienes, such as allyl methacrylate, where the two double bonds have significantly different reactivities. The polymer contains linear repeat units, rings, and pendant double bonds in relative amounts determined by kc/kp. The pendant double bonds eventually react to yield a crosslinked structure. Reactants with more than two double bonds per molecule,... 

Copolymers and terpolymers of ethylene and propene, commonly known as EPM and EPDM polymers, respectively, are useful elastomers [Ver Strate, 1986], EPM and EPDM are acronyms for ethylene-propene monomers and ethylene-propene-diene monomers, respectively. The terpolymers contain up to about 4 mol% of a diene such as 5-ethylidene-2-norbomene, dicyclopentadiene, or 1,4-hexadiene. A wide range of products are available, containing 40-90 mol% ethylene. The diene, reacting through one of its double bonds, imparts a pendant double bond to the terpolymer for purposes of subsequent crosslinking (Sec. 9-2b). 

As the reaction proceeds to higher conversions, the unreacted pendant double bonds eventually become shielded in the microgel regions, and the reactivity of the monomeric double bond approaches, and in some cases sur-... 

When characterizing polymer networks, the following definitions are typically applied [150] and are illustrated in Fig. 7. When a radical on a polymer chain propagates through a pendant double (i.e. a double bond from a monomer with one double bond already reacted), a crosslink, secondary cycle, or primary cycle can be formed. A crosslink forms when the radical reacts with a pendant... 

Fig. 7. Classification of the reactions of pendant double bonds during free radical crosslinking polymerizations...

Kinetic gelation models [178] have been used to determine, within experimental error, the fraction of constrained and unconstrained double bonds over a wide range of conversions in the polymerization of ethylene glycol dimethacrylate. The amount of unconstrained and constrained functional groups was determined experimentally by solid state nuclear magnetic resonance spectroscopy. The rules for determining constraint in the model were that all pendant double bonds and all monomers in pools of six or less are constrained. Monomers in pools of seven or more are assumed to be unconstrained. Whether a site is constrained or not does not affect the reactivity only the analysis of the model is affected by the rules defining constraint. 

PolyHIPE, in granular form, has recently been employed as a support for bicatalyst systems [136]. Styrene/DVB porous polymers were prepared with free vinyl groups (acryloyl, allyl and vinylbenzyl) on the surfaces of the cavities. Impregnation with solutions of quaternary onium monomers, with subsequent polymerisation, resulted in grafting onto the pendant double bonds, to give a surface-quaternised material (Fig. 19). 

In an analogous process polystyrene bound aryl halides, containing a pendant double bond were ring closed, giving the seven membered lacton as the major product (5.7.)7... 

Besides the synthetic route depicted in 5.5. the seven membered central heterocyclic ring of iboga alkaloids was also accessed by the palladium mediated closure of the indole derivative bearing a pendant double bond shown in 5.21. The reaction is believed to be initiated by the palladation of indole in the 2-position followed by insertion of the double bond. Since fi-hydride elimination from the formed intermediate is blocked by the conformational rigidity of the system, the reaction stops at this stage and the addition of a reducing agent is required to remove the palladium and obtain the product.21... 

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