Acrylic monomers, substituted

There have heen many studies on the polymerizability of a-substituted acrylic monomers.3jU35 33S It is established that the ceiling temperature for a-alkoxyacrylates decreases with the size of the alkoxy group. 35 However, it is of interest that polymerizations of a-(alkoxymethyl)acrylates (67)3 15 and a-(acyloxymethyl)acrylates (68)and captodative substituted monomers (69, 70) 39 appear to have much higher ceiling temperatures than the corresponding a-alkylacrylates methyl ethacrylate, MEA). For example, methyl a-... 

Thiols react more rapidly with nucleophilic radicals than with electrophilic radicals. They have very large Ctr with S and VAc, but near ideal transfer constants (C - 1.0) with acrylic monomers (Table 6.2). Aromatic thiols have higher C,r than aliphatic thiols but also give more retardation. This is a consequence of the poor reinitiation efficiency shown by the phenylthiyl radical. The substitution pattern of the alkanethiol appears to have only a small (<2-fokl) effect on the transfer constant. Studies on the reactions of small alkyl radicals with thiols indicate that the rate of the transfer reaction is accelerated in polar solvents and, in particular, water.5 Similar trends arc observed for transfer to 1 in S polymerization with Clr = 1.4 in benzene 3.6 in CUT and 6.1 in 5% aqueous CifiCN.1 In copolymerizations, the thiyl radicals react preferentially with electron-rich monomers (Section 3.4.3.2). 

A value for the polymerization enthalpy of 21.5 kcal/mole can be used to estimate percent conversion and rates for N-substituted maleimide/vinyl ether and maleic anhydride/vinyl ether copolymerizations. A value of 18.6 kcal/mole can be used for the enthalpy of polymerization of acrylate monomers to convert heat evolution data to percent conversion. Since the molar heats of polymerization for N-substituted maleimide vinyl ether copolymerization and acrylates vary by less than 20 percent, the exotherm data in the text are compared directly. 

It is clear that any kind of addition polymerization of the norbornenyl double bond will benefit from the electronic stabilization provided by a conjugating substituent. A simple radical addition process such as is known for both styrene and acrylate monomers may be a reasonable analogy to our system. Whether this effect alone is enough to account for our observations is not clear. A possible additional effect, at least in the case of the phenyl substituted monomers, is suggested below as part of our work on polymer structure. 

The radical polymerization behavior of captodative olefins such as acrylonitriles, acrylates, and acrylamides a-substituted by an electron-donating substituent is reviewed, including the initiated and spontaneous radical homo- and copolymerizations and the radical polymerizations in the presence of Lewis acids. The formation of low-molecular weight products under some experimental conditions is also reviewed. The reactivity of these olefins is analyzed in the context of the captodative theory. In spite of the unusual stabilization of the captodative radical, the reactivity pattern of these olefins in polymerization does not differ significantly from the pattern observed for other 1,1-disubstituted olefins. Classical explanations such as steric effects and aggregation of monomers are sufficient to rationalize the observations described in the literature. The spontaneous polymerization of acrylates a-substituted by an ether, a thioether, or an acylamido group can be rationalized by the Bond-Forming Initiation theory. 

Substitution of the proton by methyl in acrylic monomers is not accompanied by reduced reactivity of the methylated derivative. Bolshakov et al. have shown that the low rate of, for example, methacrylate or methacrylamide polymerizations at temperatures of 100-120 K in melting ethanol is caused by the low reactivity of the resulting active centres [129],... 

This picture is also consistent with the fact that, in general, to becomes shorter on increasing the content of tertiary amine co-units in the copolymer [118]. The observation that Rcmax decreases in poly(MBA-co-DAPA) and poly(MBA-co-DEPA) on increasing the content of tertiary amine co-units and that the minimum activity is observed in poly(MBA-co-DMEA) and poly(MBA-co-DEEA) in correspondence with the highest content of tertiary amine co-imits [118] can easily be explained. In fact, due to the mechanism proposed in Scheme 29, as soon as the traces of oxygen are consumed, the residual amine co-units, in excess with respect to MBA units, continue the conversion of the substituted benzyl-type polymeric radicals into the alkylamino radicals, which are known to display lower reinitiation constants for acrylic monomers. 

Ethenylbenzene is not the only ethenyl bonded monomer capable of undergoing copolymerization with diethenylbenzene (divinylbenzene), but commercially, the propenoic (acrylic) monomers are the alternatives which have been most widely exploited, since about 1950. For example, the methacrylic-divinylbenzene weakly acidic cation exchange resin [—RG(CH3)COOH] is made by copolymerizing diethenylbenzene and methylpropenoic acid (methacrylic acid) as shown in Scheme 2.3. Various alkyl substituted propenoic acid monomers may be employed in the manufacture of weakly acidic cation exchange resins, as are propenonitriles (acrylonitriles) and alkyl propenoates (acrylic esters). In the case of the two latter cited... 

The substituted oxazoiidone (IV) is especiaiiy useful as building block for acrylic monomers syntheses or for pharmaceuticals. 

Additions occur more easily if a carbanion with resonance or inductive stabilization is formed in the addition. Thus, fulvenes are very reactive, vinylsilanes and highly fluorinated alkenes somewhat less so. Styrene, 1,3-dienes, and enynes are more reactive than isolated alkenes, and Grignard reagents may be used to initiate anionic polymerization of styrenes, dienes, and acrylic monomers. Strained alkenes such as norbornenes and cyclopropenes are also more reactive. Examples of additions facilitated by resonance or substitution are shown in Scheme 8. 

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. 

Polyacrylate, a thermoplastic polymer, synthesized by polymerization of acrylate monomers, consists of acrylic acid (AA) esters shown in Figure 1 as the general stractirre. Methacrylate monomer differs from the acrylate monomer in that the H atom at the virtyl oxygen is substituted by a methyl group (-CH ). The wide variety of side chains and the variations in tactidty contribute to polyacry-... 

In addition, when used to photoinitiate the polymerization of acrylic monomers, low concentrations of N-substituted maleimide coupled with isopropylthioxanthone and a tertiary amine system result in markedly increased rates of polymerization, faster than the traditional isopropyl-thioxanthone/amine system alone (see the next section). Maleimides can also be used in combinations with a diarylketones and amines to initiate polymerization. ... 

It may be noted that lipases are also commonly used for the synthesis of organic compounds, including monomers and reactive oligomers. For example, Kaira et al (32) prepared vinylethylglucoside, and Gu et al (33) prepared substituted acrylic monomers, both with lipases. These monomers were subsequently polymerized by conventional methods. 

Substituted acrylic monomers. The reactants (methyl acrylate plus alcohol or amine) were added neat or in a non-aqueous solvent together with Novozym 435 immobilized lipase from Candida antarctica as a catalyst. Molecular sieves (4A) were used to remove water in order to shift the reaction equilibrium to product formation, and also to eliminate side reactions due to Michael addition that was usually enhanced by the presence of water or methanol. Unreacted starting materials were removed by evaporation, and the monomer products obtained without further purification. TLC analysis indicated that the desired products had formed. The purity of the products was confirmed by NMR and IR analysis. The two monomers were successfully polymerized in a separate step. 

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