Michael addition, polymerization

Leong et al. evaluated a hyperbranched poly(amino ester) synthesized in a novel A3+2BB B approach by Michael addition polymerization of trimethylol-propane triacrylate (TMPTA) (A3-type monomer, triacrylate), with a double molar of l-(2-aminoethyl) piperazine (AEPZ) (BB B -type monomer, trifunctional amine) (Fig. 11) [127]. To check its DNA condensation behavior and cytotoxicity, the poly(TMPTAl-AEPZ2) obtained was protonated. Due to the protonation ability of... 

GTP constitutes an example of Michael addition polymerization involving the addition of a silyl ketone acetal to a,p-unsaturated carbonyl compounds in the presence of a nucleophilic or Lewis acid catalyst Due to the living nature of GTP, the method was applied successfidly to the synthesis of well-defined random, block-graft, star-shaped polymers as well... 

Polymerizations of multifunctional monomers of suitable unequal reactivity have been proved to be feasible for preparing hyperbranched polymers. Wu et al. [163] have reported in situ C NMR monitoring of the synthesis of hyperbranched poly(aminoester)s prepared via the Michael addition polymerization of a triacrylate, trimethylolpropane triacrylate (TMPTA) (A3-type monomer) with a double molar l-(2-aminoethyl)piperazine (AEPZ) (BB B"-type monomer) in chloroform at room temperature. 

Carriers similar to the conjugates shown in 32 were synthesized by Michael addition polymerizations or from polysuccinimide by a two-step ring-opening procedure. These carriers contain 1,2-dicarboxyl-fimctional anchoring sites in the side groups. They can be platinated to make structures like those in 49, derived from 48, and 50. 

GTP is an example of Michael addition polymerization involving the addition of a silyl ketene acetal to a,P-unsaturated carbonyl compounds. A typical polymerization scheme is illustrated in Scheme 1, using methyl methacrylate as the monomer and (l-methoxy-2-methyl-l-propenoxy) trimethyl silane (MTS) as the initiator in the presence of an anionic catalyst. 

A number of BMI resias based on this chemistry became commercially available through Rhc ne Poulenc for appHcation ia priated circuit boards and mol ding compounds and Rhc ne Poulenc recognized the potential of bismaleimides as building blocks for temperature-resistant thermoset systems. The basic chemistry, however, was not new, because the Michael addition reaction had been employed by Du Pont to obtain elastomeric reaction products from bismaleimides and Hquid polymeric organic diamines (15). 

Additive Polyimides. Rhc ne-Poulenc s Kin el molding compound and Kerimid impregnating resin (115), Mitsubishi s BT Resins (116), and Toshiba s Imidaloy Resin (117) are based on bismaleimide (4) technology. Maleic anhydride reacts with a diamine to produce a diimide oligomer (7). Eurther reaction with additional diamine (Michael addition) yields polyaminohismaleimide prepolymer with terminal maleic anhydride double bonds. Cure is achieved by free-radical polymerization through the terminal double bonds. 

A very efficient method for annulations158 is based on the addition of lithium or silyl enolates to a-silylated enones as a key step. The diastereoselective 1,4-addition is followed by an aldol condensation. This procedure allows Michael additions under aprotic conditions, whereby the silyl substituent stabilizes the enolate of the Michael adduct preventing polymerization of the enone, 59 l63. 

When the cnolate of an enone is brought into reaction with an enone, usually a carbocyclic system is prepared by two consecutive Michael additions (M1MIRC reactions). Due to the lower temperatures employed and the absence of diene polymerization these reactions are useful alternatives for Diels-Alder reactions and proceed in general with high diastereoselectivities. When neither enolate nor enone is cyclic a monocyclic system is formed 338 which can be converted into a bicyclic system when the Michael addition is followed by an aldol reaction339. When, however, the enolate is cyclic a bicyclic or a tricyclic system is formed340 341. 

The Michael addition of alkoxides to nitroalkenes gives generally a complex mixture of products due to the polymerization of nitroalkenes.16 The effect of cations of alkoxides has been examined carefully, and potassium- or sodium-alkoxides give pure p-nitro-ethers in 78-100% isolated yield (Eqs. 4.12 and 4.13).17 When lithium-alkoxides are employed, the yields are decreased to 20-40%. 

The controlled polymerization of (meth)acrylates was achieved by anionic polymerization. However, special bulky initiators and very low temperatures (- 78 °C) must be employed in order to avoid side reactions. An alternative procedure for achieving the same results by conducting the polymerization at room temperature was proposed by Webster and Sogah [84], The technique, called group transfer polymerization, involves a catalyzed silicon-mediated sequential Michael addition of a, /f-unsaluralcd esters using silyl ketene acetals as initiators. Nucleophilic (anionic) or Lewis acid catalysts are necessary for the polymerization. Nucleophilic catalysts activate the initiator and are usually employed for the polymerization of methacrylates, whereas Lewis acids activate the monomer and are more suitable for the polymerization of acrylates [85,86]. 

Main group organometallic polymerization catalysts, particularly of groups 1 and 2, generally operate via anionic mechanisms, but the similarities with truly coordinative initiators justify their inclusion here. Both anionic and coordinative polymerization mechanisms are believed to involve enolate active sites, (Scheme 6), with the propagation step akin to a 1,4-Michael addition reaction. 

At the first step, the insertion of MMA to the lanthanide-alkyl bond gave the enolate complex. The Michael addition of MMA to the enolate complex via the 8-membered transition state results in stereoselective C-C bond formation, giving a new chelating enolate complex with two MMA units one of them is enolate and the other is coordinated to Sm via its carbonyl group. The successive insertion of MMA afforded a syndiotactic polymer. The activity of the polymerization increased with an increase in the ionic radius of the metal (Sm > Y > Yb > Lu). Furthermore, these complexes become precursors for the block co-polymerization of ethylene with polar monomers such as MMA and lactones [215, 217]. 

Superoxide anion formed in situ in a solution exposed to air (i.e. with only a small concentration of O2) has been used as an EGB to generate nitroalkane anions that may add to activated alkenes or to carbonyl compounds [130, 131]. An example is shown in Scheme 33. The reaction is catalytic since the product anion can act as a base toward the nitroalkane. Using the nitroalkane as the solvent favors the proton transfer pathway over the competing addition of the product anion to a second molecule of activated alkene, a pathway that may lead to polymerization [130]. In some cases, better yields of the Michael addition product were obtained if a stoichiometric amount of the anion was formed ex situ (with O2 as the PB), and the activated alkene added subsequently ]130, 132]. 

Another advantage of this method is that no catalyst is needed for the addition reaction this means that the base-catalyzed polymerization of the electrophilic olefin (i.e., a,j8-unsaturated ketones, esters, etc.) is not normally a factor to contend with, as it is in the usual base-catalyzed reactions of the Michael typCi It also means that the carbonyl compound is not subject to aldol condensation which often is the predominant reaction in base-catalyzed reactions. An unsaturated aldehyde can be used only in a Michael addition reaction when the enamine method is employed. 

Group-transfer polymerizations make use of a silicon-mediated Michael addition reaction. They allow the synthesis of isolatable, well-characterized living polymers whose reactive end groups can be converted into other functional groups. It allows the polymerization of alpha, beta-unsaturated esters, ketones, amides, or nitriles through the use of silyl ketenes in the presence of suitable nucleophilic catalysts such as soluble Lewis acids, fluorides, cyanides, azides, and bifluorides, HF. ... 

In an equally distinguished example, Langer et al. demonstrated the synthesis of a 140-membered library of degradable polymers from diacrylate and amine monomers (compare Fig. 6) that were polymerized via aza-Michael addition chemistry [80],... 

Alternatively, 3-substituted 2-carbomethoxycyclopentanones have been prepared by Michael addition to 2-carbomethoxycyclopentenone. " However, this Michael acceptor is unstable, difficult to prepare, and polymerizes in the presence of many nucleophiles. A longer synthesis of 2-carbomethoxy-3-vinylcyclopentanone has been reported. The general route to 2-carbomethoxy-3-vinylcyclopentanones developed by Trost has the advantage of producing these compounds in optically active form. 

Although transfection efficiencies was low, Lim et al. (1) prepared hyperbranched polyaminoesters, (I), using Michael addition of ethanolamine with methyl acrylate followed by bulk polymerization. 

Other authors have described the lipase-catalyzed chemoselective acylation of alcohols in the presence of phenolic moities [14], the protease-catalyzed acylation of the 17-amino moiety of an estradiol derivative [15], the chemoselectivity in the aminolysis reaction of methyl acrylate (amide formation vs the favored Michael addition) catalyzed by Candida antarctica lipase (Novozym 435) [16], and the lipase preference for the O-esterification in the presence of thiol moieties, as, for instance, in 2-mercaptoethanol and dithiotreitol [17]. This last finding was recently exploited for the synthesis of thiol end-functionalized polyesters by enzymatic polymerization of e-caprolactone initiated by 2-mercaptoethanol (Figure 6.2)... 

The maleimide group can undergo a variety of chemical reactions. The reactivity of the double bond is a consequence of the electron withdrawing nature of the two adjacent carbonyl groups which create a very electron-deficient double bond, and therefore is susceptible to homo- and copolymerizations. Such polymerizations may be induced by free radicals or anions. Nucleophiles such as primary and secondary amines, phenates, thiophenates, carboxylates, etc. may react via the classical Michael addition mechanism. The maleimide group furthermore is a very reactive dienophile and can therefore be employed in a variety of Diels Alder reactions. Bisdienes such as divinylbenzene, bis(vinylbenzyl) compounds, bis(propenylphenoxy) compounds and bis(benzocyclobutenes) are very attractive Diels Alder comonomers and therefore some are used as constituents for BMI resin formulations. An important chemical reaction of the maleimide group is the ENE reaction with allylphenyl compounds. The most attractive comonomer of this family is DABA particularly when tough bismaleimide resins are desired. 

The typical reaction is Michael addition of nucleophiles thus, 1-vinylpyridinium ion (967) adds A-, S- and C-nucleophiles to give products of type (968). A-Vinyl groups can also undergo polymerization. 

Bicyclic bridged phosphorinane derivatives can be synthesized by different methods. When phenylphosphine is heated with cycloocta-2,7-dienone to 135 °C in the presence of polymerization inhibitors, e.g. hydroquinone, and the double Michael addition product is oxidized, the two crystalline syn and anti isomers (total yield 48-59%) are isolated. Separation by crystallization gives the pure compounds which can in turn be transformed at the carbonyl or the phosphorus group (equation 10) (75T33,76JOC589). 

The overall rate of polymerization Rp of barium acrylate (BA) polymerization sensitized by MB in the presence of varying amounts of j>-toluene sulfinate sodium sslt (PTSS) was shown to depend on the square root of the absorbed light intensity and to exhibit a complex second order dependence on the concentration of sulfinate and monomer (43). The latter dependence was shown to result from a desensitization process described by eq. 16 in which PTSS undergoes Michael addition to the acrylate monomer. 

The anion generated by a Michael addition can also be trapped by another Michael addition. Obviously, continued repetition of this process produces polymeric esters, nitriles, etc., in a typical anionic poly-... 

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