Anionic chain polymerization-anion radical transfer

C. Formation of MAIs By Anionic Chain Polymerization-Anion Radical Transfer... 

Regarding anion radical transfer, low-molecular weight azo compounds were used as terminating agents in anionic polymerizations. An interesting example is the addition of a living polystyrene chain to one nitrile group of AIBN [71]. The terminal styryl anion is likely to form... 

You will need to make a steady-state assumption that the concentration of anion radicals is constant (and you should also note that [Na+] = [NH2 ]). But you re not done yet Now if you assume that the number average degree of polymerization is equal to the average number of monomers added to an anion before chain transfer to NH3, derive Equation 4-46. 

Chain polymerization involves three processes chain initiation, chain propagation, and chain termination. (A fourth process, chain transfer, may also be involved, but it may be regarded as a combination of chain termination and chain initiation.) Chain initiation occurs by an attack on the monomer molecule by a free radical, a cation, or an anion accordingly, the chain polymerization processes are called free-radical polymerization, cationic polymerization, or anionic polymerization. A free radical is a reactive substance having an unpaired electron and is usually formed by the decomposition of a relatively unstable material called an initiator. Benzoyl peroxide is a common free-radical initiator and can produce free radicals by thermal decomposition as... 

In principle, the appearance of electron donor groups near the double bond of the monomer leads to a cationic mechanism, while positive groups that withdraw electrons mostly lead to the anionic process. An increase of temperature usually leads to a decrease in rate of reaction or length of the chain. Polymerization always occurs in solution, wherein the solvent acts as separator of the ion-pair, and quite often as a transfer reagent. As already mentioned, most monomers undergo polymerization via free radicals, mainly when conjugated double bonds are present or substitute groups that withdraw electrons. 

Figure 15 Schematic chain polymerization mechanism involving initiation, propagation, transfer monomer, transfer to solvent, and termination by both disproportionation and recombination of propagating radicals. If the organic chemistry of this reaction is examined it will be seen more clearly that initiator fragments can be incorporated at one or both ends of the polymer chain, that disproportionation leads to unsaturation at one chain end, and that recombination gives rise to vicinal groups within a polymer chain. The precise chemistry of the chain reaction is very dependent on whether the active centre ( ) is a radical, anion, cation or other type of...

There are numerous ways of attaching polymers to a solid surface. Examples are photo cross-linking of pre-formed polymer chains, in-situ atom transfer radical polymerization (ATRP), electron beam irradiation,and plasma polymeriza-tion.f Electrochemical techniques are particularly suited for conducting substrates. For example, Palacin et al. have grafted vinylic monomers from anhydrous solutions.f This technique is mainly based on an anionic polymerization and leads to a covalent link between the polymer and the metal. Schuhmann et al. 

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