Monomers polarity effects

Alfrey and Price proposed a means of predicting monomer reactivity in copolymerization from two parameters, (a measure of resonance) and e (a measure of polar effects) (8). These parameters have been related to the reactivity ratios by equations 15—17. 

Contribution of the Polar Effect Ato the Activation Energy of the Addition of Polar Radicals to Polar Monomers CH2=CRY (Calculated from the Data of Several Studies [40,51-53])... 

Polar effects appear to be of prime importance in determining the effect of quinones. p-Benzoquinone and chloranil (which are electron-poor) act as inhibitors toward electron-rich propagating radicals (vinyl acetate and styrene) but only as retarders toward the electron-poor acrylonitrile and methyl methacrylate propagating radicals. A further observation is that the inhibiting ability of a quinone toward electron-poor monomers can be increased by the addition of an electron-rich third component such as an amine. Thus the presence of triethylamine converts chloranil from a very weak retarder to an inhibitor toward methyl methacrylate. 

Two mechanisms have been proposed to explain the strong alternation tendency between electron-acceptor and electron-donor monomers. The polar effect mechanism (analogous to the polar effect in chain transfer—Sec. 3-6c-2) considers that interaction between an electron-acceptor radical and an electron-donor monomer or an electron-donor radical and... 

An investigation into the initiation mechanism of copolymerization of ethyl vinyl ether and acrylonitrile by /-butoxyl radicals lias shown that the reaction between the two monomers competes successfully with radical trapping by the nitroxide radical trap (5).37 The /-butoxyl radicals react 3-6 times faster with ethyl vinyl ether than acrylonitrile the authors proposed that this is due to selective interaction of one monomer with the radical species rather than a solvent polarity effect. 

ItoO, Matsuda M (1979) Evaluation of addition rates of the thiyl radicals to vinyl monomers by flash photolysis. 2. Substituent effect on addition of substituted benzenethiyl radicals to methyl methacrylate or styrene. J Am Chem Soc 101 5732-5735 Ito O, Matsuda M (1981) Evaluation of addition rates of thiyl radicals to vinyl monomers by flash photolysis. 3. Polar effect in addition reactions of substituted benzenethiyl radicals. J Am Chem Soc 103 5871-5874... 

The electron transfer induced reaction of this diene system results in rapid [4 + 2]dimerization conversely, the dimer rapidly undergoes cycloreversion upon electron transfer. Both reactions result in strong CIDNP effects. The monomer polarization supports a radical cation with a spin density distribution like those of the butadiene or fulvene radical cations. The dimer polarization identifies a dimer radical cation with appreciable spin density only on two carbons of the dienophile fragment this species can only be the doubly linked radical cation D [135, 136], Significantly, a second dimer radical cation is implicated in a pulsed... 

Penultimate and similar kinetic models are used nowadays principally for the treatment of the experimental data, obtained from the copolymerization of certain monomers like fumaronitrile or maleic anhydride which are characterized by rather strong steric and polar effects. 

Me and Ph are donors of electrons during addition the resonance effect prevails over polar one. Benzoyl-oxyl is an electron-acceptor radical the addition step is controlled merely by the polar effect [128]. During the addition of monomers to trimethylmethoxyl, both polar and resonance properties of their electron configuration are involved. 

In addition to this classical polarity effect, the solvent can have a more subtle influence, hi the case of monomer 16 (Fig. 20) hydrogen bonding in chloroform leads to the formation of a usual flexible supramolecular polymer. However, in dodecane the dimerization of the ureidotriazine is reinforced by a solvophobic stacking of the aromatic parts, which yields a columnar architecture [93]. A similar solvophobic effect has been demonstrated with a UPy-based monomer [94]. Another possible side effect of the nature of the solvent is the occurrence of specific host-guest interactions between the HBSP and the solvent [42,95,96]. 

Soga and co-workers examined the relation between the Hammett s a value of each substituent and the reactivities in copolymerization (Figure 17.8). It is observed that the monomer reactivity is enhanced by electron-releasing substituents in the aromatic ring. Even />-ter/-butylstyrene with a substituent of large steric hindrance shows a high reactivity. This indicates that there is a strong polar effect of the substituent on the rate of addition [28]. Similar effects were observed by Ishihara et al. in the homopolymerization of these monomers [27]. 

Zuikov and Soloviev (1979) studied the effect of monomer polarity on both the size and the size distribution of particles in the forming latexes. As a criterion of polarity they took the solubility of the monomer in water, which in this case has an independent significance as well. Polymerizations of styrene, methyl methacrylate, butyl methacrylate, and methyl acrylate... 

Eq. 94 can be used to analyze the effect of errors in the approximate quantities (functionals and potentials) on the interaction energy in weakly interacting complexes. The first six terms represent the zeroth-order contribution to the error i.e. do not account for the complexation induced change of the electron densities of the isolated monomers. Such terms can be expected to be dominant for weak complexes in the absence of strong electrostatic and polarization effects. Terms from the seventh to ninth represent the first-order contribution. Their relative significance increases... 

Problem 7.9 Explain the following copolymerization results or observed behaviors considering the influence of resonance, steric, and polar effects on monomer reactivity ... 

In practice, (f) can be calculated by inserting experimental copolymerization rates into Eq. (7.64). The values of (j> thus obtained are frequently greater than unity, and these deviations are ascribed to polar effects that favor cross-termination over homotermination. However, this is not always unambiguous, since the apparent cross-termination factor may vary with monomer feed composition in a given system [25,26]. It is clear also that termination reactions are at least partially diffusion controlled [27,28]. A dependence of segmental diffusivity on the structure of macroradicals is to be expected and dependence of diffusion controlled termination on copolymer composition seems reasonable. It is therefore plausible that the value of the overall termination rate constant ku in copolymerizations should be functions of fractions F and Fi) of the comonomers incorporated in the copolymer. An empirical expression for ku has thus been proposed [27] ... 

Considering resonance and polarity effects what type of monomers would you choose to copolymerize with vinyl ethers ... 

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