Vinyl addition

The most important reactions of acrylamide are those that produce vinyl addition polymers (see Acrylamide polymers). The initiation and... 

Polymerization. Isoprene polymeri2ation can proceed by either 1,4- or l,2-(vinyl)addition (see Elastomers, synthetic-polyisoprene). 

Addition leads to two possible stmctures which differ in the configuration of the remaining double bond. Vinyl addition produces two other possible stmctures, depending on whether the 1,2- or the 3,4- double bond takes part in the polymeri2ation reaction. 

Cyanoethylation. One of the eadiest examples of etherification of ceUulose by an unsaturated compound through vinyl addition is the cyanoethylation of cotton (58). This base-cataly2ed reaction with acrylonitrile [107-13-1/, a Michael addition, proceeds as foUows ... 

In some cases, diene polymers (for instance polychloroprene rubbers) can add to the growing polymer chain by 1,2 addition (also called vinyl addition). This creates labile hydrogen or reactive halogen on tertiary carbon atoms. A few percent of this type of structure in the rubber will assist cross-linking reactions. 

The obviation of side reactions is essential to the success of ADMET, and this can be realized if the proper catalyst is chosen. Catalyst choice must avoid the possibility of cation formation,13 vinyl addition, and/or formation of multiple catalytic species, all of which are detrimental to clean metathesis chemistry. Over the past 10 years, our group has utilized a variety of different catalysts, several of which are illustrated in Fig. 8.4. 

Thermal Effects in Addition Polymerizations. Table 13.2 shows the heats of reaction (per mole of monomer reacted) and nominal values of the adiabatic temperature rise for complete polymerization. The point made by Table 13.2 is clear even though the calculated values for T dia should not be taken literally for the vinyl addition polymers. All of these pol5Tners have ceiling temperatures where polymerization stops. Some, like polyvinyl chloride, will dramatically decompose, but most will approach equilibrium between monomer and low-molecular-weight polymer. A controlled polymerization yielding high-molecular-weight pol)mier requires substantial removal of heat or operation at low conversions. Both approaches are used industrially. 

Vinyl addition polymerizations, being chain reactions, are more complex than condensation polymerizations and they are generally more likely to include minor side reactions leading to branching or cross-linking. The structures of the pol3oneric products are consequently more difficult to establish with certainty. 

Substituted ethylenes in which substituents occur on both carbon atoms (with the exception of the fluoroethylenes) usually are not prone to polymerize, although some of them, such as the maleates and fumar-ates, copolymerize readily with other monomers. The further fact that, with rare exceptions, the monomers unite through the addition of the substituted carbon atom of one unit to the unsubstituted carbon atom of the next permits representation of nearly all vinyl addition polymers by the general structural formula... 

The difficulties of devising a basis for conveniently classifying various polymerizations in an appropriate manner have been discussed earlier in this chapter and several borderline examples which offer particular difficulty have been mentioned. One of these, the polymerization of the N-carboxyanhydrides, falls within the definition of a condensation polymerization, proceeds by a mechanism resembling a vinyl addition polymerization, and yields a product which possesses the structure of a typical condensation polymer. Definitions have been... 

BRANCHING AND CROSS-LINKING IN VINYL ADDITION POLYMERS... 

Vinyl addition leaving multiple formyl groups for coupling... 

Schiff base interactions between aldehydes and amines typically are not stable enough to form irreversible linkages. These bonds may be reduced with sodium cyanoborohydride or a number of other suitable reductants (Chapter 2, Section 5) to form permanent secondary amine bonds. However, proteins crosslinked by glutaraldehyde without reduction nevertheless show stabilities unexplainable by simple Schiff base formation. The stability of such unreduced glutaraldehyde conjugates has been postulated to be due to the vinyl addition mechanism, which doesn t depend on the creation of Schiff bases. 

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