Allylic polymerization

Compounds possessing allylic structures polymerize by free-radical mechanism only to low molecularweight oligomers. In some cases the products consist mostly of dimers and trimers. The DP for poly(allyl acetate), for instance, is only about 14. This is due to the fact that allylic monomer radicals are resonance-stabilized to such an extent that no extensive chain propagations occur. Instead, there is a large amount of chain transferring. Such chain transferring essentially terminates the reactions [151]. The resonance stabilization can be illustrated on an allyl alcohol radical  

The hydrogen transfer takes place from the allylic hydrogen, as shown on allyl acetate  

In this case, transfer can also take place to the acetate moiety  

In spite of degradative chain transferring, polyallyl compounds can be readily polymerized by a free-radical mechanism into three-dimensional lattices. High DP is not necessary to achieve growth in three dimensions. An example of such polyallyl compounds is triallyl phosphate  

Many other polyallyl derivatives are offered commercially and are described in the trade literature. 

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As can be seen in Fig. 1, no gel effect was observed even beyond the gel point in contrast to the polymerization of common multivinyl compounds such as EDMA [6]. This unusual polymerization behavior is characteristic of allyl polymerization, in which monomer chain transfer is essentially a termination reaction [42] in contrast to bimolecular termination of growing polymer radicals in common vinyl polymerization. In other words, primary chain length is quite short and kept nearly constant during polymerization as is required for the application of Eq. (4). 

We have investigated the free-radical polymerization of a variety of diallyl dicarboxylates extensively, especially DAP, DAI, and DAT, in terms of allyl polymerization, cyclopolymerization, and gelation [38]. The cyclopolymerization resulted in cyclization constants Kc of 7.5, 1.6, and 0.6 mol/L at 60 °C for DAP, DAI, and DAT, respectively. In this coimection, it should be noted that in the polymerizations of DAP, DAI, and DAT, two different modes of intramolecular cyclization should be considered. The cyclization reaction of DAP... 

The most significant difference between allyl and vinyl polymerizations is in the length of their primary chains which has a predominant influence on gelation, since in the allyl polymerization an occurrence of monomer chain transfer is quite remarkable and only the oligomer is formed. Therefore, we tried to carry out the telomerization of EDMA in the presence of CBr4 in order to reduce the primary... 

Allyl compounds polymerize with considerably more difficulty than analogous vinyl compounds. The most characteristic feature in allyl polymerization is the formation of stable allylic radicals, only a fraction of which participate in further pol]nnerization. They are generally produced by the abstraction of a hydrogen/Stom by the catalyst radical [reaction (1)] or by a chain transfer. 

What is allylic polymerization If allyl alcohol does not polymerize to a high molecular polymer by free-radical polymerization, why does triallyl cyanurate form a high molecular weigh network structure by the same mechanism ... 

Most vinyl and acrylic compounds more or less obey ideal polymerization kinetics during free radical polymerization. Drastic deviations, however, occur for allyl polymerizations since a chain termination by monomer dominates in this case [see Equation (20-41)]. For this case, the formation of polymer free radicals is given analogously to Equation (20-51) as... 

In contrast, the kinetic chain length is found not to be dependent of monomer or initiator concentrations when termination occurs via the monomer as in allyl polymerization ... 

This chemical transfer must be distinguished from the concept of kinetic transfer (chain transfer). That is, the free radical that is newly formed by chemical transfer is not always of roughly equal activity to that which is lost. If it is inactive, then the chemical transfer is kinetically a chain termination (see allyl polymerization). On the basis of the reactivity of the new free radical compared to the monomer or added materials, then various categories are obtained (Table 20-5). 

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