Hydrogen-Transfer Polymerization of Acrylamide

The polymerization of acrylamide (or methacrylamide) by strong bases such as sodium, orga-nolithium compounds, and alkoxides yields a polymer structure 

The polymerization mechanism involves addition of the anionic initiator to the carbon-carbon double bond of the monomer 

The amide anion initiates polymerization via a similar reaction sequence by addition of L to monomer. Propagation follows in a like manner  

This polymerization follows a path that is quite different than any of the previously discussed polymerizations. The propagating center is not an ion or a radical but is the carbon-carbon double bond at one end of the propagating species LI. In addition, it is not the monomer but 

Isocyanates are polymerized through the carbon-nitrogen double bond to 1-nylons by anionic initiators such as metal alkyls, sodium naphthalene, and sodium cyanide [Bur and Fetters, 

CH2=CHCONH— CH2 - CHCONH- - CH2CH2CONH -) H CH2=CHC0NH-(-CH2CH2C0NH H + CH2=CHC0NH 

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Acrylamide readily undergoes polymerization by conventional free radical methods, ionizing radiation, ultrasonic waves, and ultraviolet radiation. The base-cata-lized hydrogen transfer polymerization of acrylamide yields poly-/3-alanine (Nylon 3) a water insoluble polymer that is soluble in certain hot organics. All current industrial production is believed to be by free radical polymerization. 

We have applied this process to the direct polycondensation reaction of 0-alanine to obtain high molecular weight poly(0-alanine) which is difficult to prepare by the NCA method, and has been produced from alternative monomers, e.g. by the ringopening polymerization of 0-propiolactam 2or hydrogen-transfer polymerization of acrylamide 26). 

Cis and trans crotonamides can also polymerize by hydrogen transfer polymerization. Sodium r-butoxide in pyridine yields identical polymers from both isomers. Also, hydrogen transfer polymerization of acrylamide with optically active, basic catalysts yields optically active polymers. The reactions can be carried out in toluene, using optically active alcotxolates of amyl alcohol. The initiating ability of the metal ions is in the following order, Na > Ba > Ca > Mg > Al. Optically active polymethacrylamide forms with optically active barium and calcium alcoholates, but not with the other cations.In this reaction, however, the asymmetric synthesis takes place... 

Discuss and illustrate hydrogen transfer polymerization of acrylamide. 

Nylon 5 can be synthesized by intramolecular hydrogen transfer polymerization of acrylamide" (see chapter 3) ... 

Method of synthesis hydrogen transfer polymerization of acrylamide in the presence of anionic catalyst vinyl polymerization is side reaction, which can be prevented if tert-BuOK catalyst is finely dispersed in polymerization solvents Masamoto, J, Memoirs of Fukui University of Technology, 3,1,291, 2003. 

A special case is the hydrogen-transfer polymerization of acrylamide or methacrylamide leading to a polyamide. The synthesis of an optically active, "partially stereoregular" poly-methyl-3-alanine by polymerization of methacrylamide with an optically active basic catalyst has been reported (24). 

Breslow et al. reported that nylon-3 ( sometimes described as nylon 3 or poly- p -alanine) is obtained using hydrogen transfer polymerization of acrylamide in the presence of an anionic catalyst ... 

Various methods for the preparation of nylon-3 are reported in references and patents. Among the methods, the hydrogen transfer polymerization of acrylamide is very interesting from both the academic and industrial viewpoints. 

Morgenstem and Berger also reported that a nearly pure nylon- 3 was produced using the hydrogen transfer polymerization of acrylamide [13]. They confirmed these results using an NMR method. 

Polyacrylamide exhibits strong hydrogen bonding and water solubility. Most of the interest in this polymer is associated with this property. Polymerization of acrylamide monomer is usually conducted in an aqueous solution, using free-radical initiators and transfer agents. 

It is well known that acrylates and methacrylates, a,jS-unsaturated esters, readily undergo vinyl polymerization under radical and anionic conditions. Similar to esters, radical polymerization of a,/l-unsaturated amides, such as acrylamide, methacrylamide, and their /V-monoalkyl-substituted derivatives, proceed in vinyl addition modes, while anionic vinyl polymerization is often accompanied by hydrogen-transfer polymerization due to the highly acidic amide hydrogen of these monomers (Breslow et at, 1957 Kennedy and Otsu, 1972). As described above, a variety of A/,A-diaIkylacrylamides are capable of radical and anionic polymerization to afford vinyl polymers. 

In the base catalyzed polymerization of acrylamide, the vinyl polymerization is reported by Nakayama et al. [7] to occur in addition to the hydrogen transfer polymerization process. 

If we hypothesize that the hydrogen transfer polymerization product of acrylamide is the polymeric structural material of nylon-3, then the following two points arise as potentially serious problems. 

The propagating center is neither an ion nor a radical, but a carbon to carbon double bond at the end of the chain. The monomer anion adds to this double bond. This process is a step-growth polymerization and the monomer anion is called an activated monomer. Not all acrylamide polymerizations, initiated by strong bases, however, proceed by a hydrogen transfer process. Depending upon reaction conditions, such as solvent, monomer concentration, and temperature some polymerizations can take place through the carbon to carbon double bonds [216]. 

Breslow et al.[l] found that when acrylamide was polymerized in the presence of a strong base catalyst, the polymerization occurred with hydrogen transfer, and nylon-3 was obtained. 

Polar vinyl monomers that contain labile hydrogen such as (meth)acrylic acid, hydroxyethyl methacrylate, and (meth)acrylamide cannot be used directly for anionic polymerization as they can act as a terminator via proton transfer to the reactive anions. They can be subjected to anionic polymerization only after appropriate protection of these functional groups into nonreactive groups toward anions, for example, by esterification or silylation. " A detailed list of protected monomers is given in various reviews. 

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