Acrylamide, anionic polymerization

It might be noted that most (not all) alkenes are polymerizable by the chain mechanism involving free-radical intermediates, whereas the carbonyl group is generally not polymerized by the free-radical mechanism. Carbonyl groups and some carbon-carbon double bonds are polymerized by ionic mechanisms. Monomers display far more specificity where the ionic mechanism is involved than with the free-radical mechanism. For example, acrylamide will polymerize through an anionic intermediate but not a cationic one, A -vinyl pyrrolidones by cationic but not anionic intermediates, and halogenated olefins by neither ionic species. In all of these cases free-radical polymerization is possible. 

Polyacrylics are produced by copolymerizing acrylonitrile with other monomers such as vinyl acetate, vinyl chloride, and acrylamide. Solution polymerization may be used where water is the solvent in the presence of a redox catalyst. Free radical or anionic initiators may also be used. The produced polymer is insoluble in water and precipitates. Precipitation polymerization, whether self nucleation or aggregate nucleation, has been reviewed by Juba. The following equation is for an acrylonitrile polymer initiated by a free radical ... 

Acrylamides represent still another interesting class of monomers.6 Their anionic polymerization may be initiated by strong bases, like, e.g., amides. The growing chain contains the unit —CH2—CH —CO—NH2 and intramolecular proton transfer competes efficiently with its carbanionic growth. Since the rearrangement... 

The anionic polymerization of lactams proceeds by a mechanism analogous to the activated monomer mechanism for anionic polymerization of acrylamide (Sec. 5-7b) and some cationic polymerizations of epoxides (Sec. 7-2b-3-b). The propagating center is the cyclic amide linkage of the IV-acyllactam. Monomer does not add to the propagating chain it is the monomer anion (lactam anion), often referred to as activated monomer, which adds to the propagating chain [Szwarc, 1965, 1966]. The propagation rate depends on the concentrations of lactam anion and W-acy I lactam, both of which are determined by the concentrations of lactam and base. 

The products of the (e q + RCH=CH2) reaction are RCH—CH2 earbanions. Some of these have been identified by their chemical reactivity. Others have been observed through their absorption spectra by means of pulse-radiolysis techniques. The carbanion of acrylamide, for instance, has been shown to dimerize, to react with other free radicals, inducing anionic polymerization, and to react with oxygen, Ag+ and Fe(CN) - ions, presumably by electron-transfer reactions (Chambers et al., 1967). The absorption spectrum of the product of the (dimethyl fumarate + ey5) reaction has been observed in alkaline solution. The rate... 

Helix-sense-selective anionic polymerization of acrylates TrA (32) and PDBSA (33)97 98 and acrylamides including the series of A/A -diphenylacrylamides" 101 (34) have been investigated using (+)-PMP, (—)-Sp,... 

Contrary to the high reactivity of the active centers in cationic and anionic polymerizations, radical polymerizations are tolerant to many functionalities. It has been possible to polymerize a wide range of functional monomers such as substituted styrenes, functional acrylates and substituted acrylamide. 

A brief review of the radical and anionic polymerization of allyl acrylate and allyl acrylamides has appeared in Spanish [85]. 

Under certain conditions, such false monomeric units can be the major portion of the polymerized linkages in ionic polymerizations. For example, acrylamide is polymerized free radically to poly(acrylamide), but, anionically, by proton shift, to poly()8-alanine) ... 

A reversed case is found, in which the matrix polymers are formed from the reinforcing rodlike molecule [23] PPTA polyanion was used as the initiator for the anionic polymerization of acrylamide to form the nylon 3 matrix. Composite films showed greatly improved strength and modulus over unmodified nylon 3 with no loss of flexibility. The combination of various chemical reactions will bring many possibilities. 

Anionic polymerization of unsubstituted acrylamide, catalyzed by strong bases, does not yield typical vinyl polymers. Instead, the product is a 1,3-adduct, poly -alanine). " Two alternate reaction paths were originally proposed " ... 

In contrast, neither acrylamide nor N-aUcylacrylamides could be anionically polymerized, due to proton abstraction from their acidic amide protons. Among such monomers, N-isopropylacrylamide (NIPAM) is the most often used, with recent interest in its polymer - poly(N-isopropylacrylamide) (PNIPAM) - having increased in exponential fashion due to its possible use as hydrogels, in drug-delivery devices, in biomedicine, and in permeation membranes - all of which reflect the polymer s water-solubiUty and thermoresponsive nature (Tc = 32 °C). 

Anionic polymerization of lactams offers the best approach to the preparation of polyamide containing block copolymers. Styrene-nylon 6 block copolymers were prepared by adding e-caprolactam to polystyrene macroanions terminated with bisphenol A bis(chlorofor-mate)(31). Yamashita prepared ABA block copolymers of styrene-a-pyrrolidone and styrene- -caprolactam by sequential addition to styrene macroanions( ). Similarly Stehlik and Sebenda prepared N-acrylamide containing block copolymers(33). Block copolymers of isoprene-pivalolactam have also been reported( . In these cases the lactam was added to "living" polyisoprene anions. 

Similarly to the poly(acrylamide)s and poly(vinyl amide)s, POEGMA can be prepared by free radical polymerization, CRP and anionic polymerization, whereby the latter two methods result in well-defined polymer structures with defined end-groups. Even though CRP of OEGMA can be performed by ATRP and RAFT polymerization (Becer et al, 2008 Lutz and Hoth, 2006a), the methacrylate obstructs OEGMA homopolymeriza-tion by nitroxide mediated polymerization. This can, however, be overcome by copolymerization with a minor amount of styrenic comonomer that enables good control over the polymerization (Charleux et al., 2005 Lessard et al., 2012). 

Free radical or anionic polymerization is possible and can gel using a crosslinking agent (N,N -methylene bis acrylamide, divinyl benzene, etc.) that has a multifunctional group. Various copolymerized crosslinked materials can be obtained by comonomers. 

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. 

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. 

Remarkably, for the radical polymerization of N,N-disubstituted acrylamides, such as DMA (which are polymerizable directly with anionic and coordination processes), the isotactic control afforded by LAs is comparable to that obtained via anionic polymerization under much more demanding conditions. For instance, Okamoto and coworkers reported that an isotactic content of m = 88% could be obtained during the radical polymerization of DMA in methanol at 0 °C by using 10 mol% Yb(OTf)3 as a control agent. Subsequent work by Matyjaszewski and coworkers... 

Experimental work on molecular composites has focused on attempting to kinetically delay the phase separation with a desirable morphology before the thermodynamics leads to complete immiscibility. Most of this work was initially performed as part of a program sponsored by the United States Air Force. For example, poly (p-phenylene terephthalamide) (PPTA) and poly (p-phenylene benozbisthiazole) (PBT) have been successfully dispersed in a Nylon 66 matrix.i 22 J y gf 23 reported that there are interactions present in a PPTA and Nylon 6 system and that phase separation can be thermally induced in molecular composites based on these two polymers. Thermally induced phase separation has also been observed in the PBT/ Nylon 6 system, when the melting temperature of the Nylon component is reached. Finally, Moore and Mathias reported a unique method for the preparation of molecular composites using an in situ polymerization process in which the anion of the PPTA was used as the initiator for the anionic polymerization of acrylamide in the formation of a Nylon 3 matrix. 

Radical copolymerization is used in the manufacturing of random copolymers of acrylamide with vinyl monomers. Anionic copolymers are obtained by copolymerization of acrylamide with acrylic, methacrylic, maleic, fu-maric, styrenesulfonic, 2-acrylamide-2-methylpro-panesulfonic acids and its salts, etc., as well as by hydrolysis and sulfomethylation of polyacrylamide Cationic copolymers are obtained by copolymerization of acrylamide with jV-dialkylaminoalkyl acrylates and methacrylates, l,2-dimethyl-5-vinylpyridinum sulfate, etc. or by postreactions of polyacrylamide (the Mannich reaction and Hofmann degradation). Nonionic copolymers are obtained by copolymerization of acrylamide with acrylates, methacrylates, styrene derivatives, acrylonitrile, etc. Copolymerization methods are the same as the polymerization of acrylamide. 

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