Anionic chain polymerization

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

Which of the following could serve as an initiator for an anionic chain polymerization (a) AICI3 H2O, (b) BF3 H2O, (c) butyllithium, or (d) sodium metal ... 

What species is produced by the reaction of an anionic chain polymerization initiator and the monomer ... 

What are the propagation species in anionic chain polymerizations ... 

What elastomer is produced by anionic chain polymerization ... 

Block copolymers have commercial potential for obtaining products that can incorporate the desirable properties of two or more homopolymers. This potential has led to an intense effort to find reaction systems that proceed as living polymerizations. Some anionic chain polymerizations proceed as living polymerizations under conditions where no viable chainbreaking reactions occur, and this has resulted in useful block copolymers (Sec. 5-4). 

Macroinitiators for ATRP can be produced from polymers obtained from non-ATRP polymerization by appropriate conversion of their end groups. For example, hydroxyl-capped polymers obtained by cationic or anionic chain polymerization or even step polymerization can be esterihed with 2-bromopropanoyl bromide to yield Br-capped polymers that are ATRP macroinitiators. 

The determination of the various rate constants (ki, kp, kt, kts, ktr) for cationic chain polymerization is much more difficult than in radical chain polymerization (or in anionic chain polymerization). It is convenient to use Rp data from experiments under steady-state conditions, since the concentration of propagating species is not required. The Rp data from non-steady-state conditions can be used, but only when the concentration of the propagating species is known. For example, the value of kp is obtained directly from Eq. (8.143) from a determination of the polymerization rate when [M J is known. The literature contains too many instances where [M" "] is taken equal to the concentration of the initiator, [IB], in order to determine kp from measured Rp. (For two-component initiator-coinitiator systems, [M" ] is taken to be the initiator concentration [IB] when the coinitiator is in excess or the coinitiator concentration [L] when the initiator is in excess.) Such an assumption holds only if Ri > Rp and the initiator is active, i.e., efficiency is 100%. Using this assumption without experimental verification may thus lead to erroneous results. 

Formaldehyde, trioxane Cationic or anionic chain polymerization Appliances, plumbing and hardware, transportation... 

In the context of the anionic polymerization of CA derivatives, as considered in Section 10.3.2.2.1, it is notable that the polymerization of cyanoacrylates is also photoinitiated by substituted pyridine pentacarbonyl complexes of tungsten or chromium, i.e. M(CO)5L with M = Cr or W, and L = 2- or 4-vinylpyridine [60]. Photo-released pyridine adds to CA, and the resulting zwitterion initiates the anionic chain polymerization (see Scheme 10.16). 

The kinetic picture of anionic chain polymerization also depends mostly upon the specific reaction. For those that are initiated by metal amides in liquid anunonia, the rate of initiation can be shown to be as follows ... 

Cyanoacrylate adhesives consist mainly of alkylcyanoacrylate monomer, which undergo rapid anionic chain polymerization when the adhesive bond is closed. Hydroxide ions in absorbed water are generally thought to be the initiators, and the rapidity of anionic polymerization is due to two electron-withdrawing groups (-CN and -COOR), which stabilize the propagating anion. The initiation step is... 

Anionic chain polymerization can be initiated by metal alkoxides, aryls and alkyls and electron-transfer from sodium naphthalene. Alkyllithiums are among the most useful, being employed commercially in the polymerization of 1,3-butadiene, isoprene, and styrene. Initiation involves addition of alkyl anion to monomer... 

The anionic chain polymerizations of polar monomers, such as methyl methacrylate, methyl vinyl ketone and acrylonitrile, often yield complex polymer structures due to nucleophilic reactions of the carbonyl and nitrile groups. 

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