Methacrylate radical

There are some indications that the situation described above has been realized, at least partially, in the system styrene-methyl methacrylate polymerized by metallic lithium.29 29b It is known51 that in a 50-50 mixture of styrene and methyl methacrylate radical polymerization yields a product of approximately the same composition as the feed. On the other hand, a product containing only a few per cent of styrene is formed in a polymerization proceeding by an anionic mechanism. Since the polymer obtained in the 50-50 mixture of styrene and methyl methacrylate polymerized with metallic lithium had apparently an intermediate composition, it has been suggested that this is a block polymer obtained in a reaction discussed above. Further evidence favoring this mechanism is provided by the fact that under identical conditions only pure poly-methyl methacrylate is formed if the polymerization is initiated by butyl lithium and not by lithium dispersion. This proves that incorporation of styrene is due to a different initiation and not propagation. 

The results of chain transfer studies with different polymer radicals are compared in Table XIV. Chain transfer constants with hydrocarbon solvents are consistently a little greater for methyl methacrylate radicals than for styrene radicals. The methyl methacrylate chain radical is far less effective in the removal of chlorine from chlorinated solvents, however. Vinyl acetate chains are much more susceptible to chain transfer than are either of the other two polymer radicals. As will appear later, the propagation constants kp for styrene, methyl methacrylate, and vinyl acetate are in the approximate ratio 1 2 20. It follows from the transfer constants with toluene, that the rate constants ktr,s for the removal of benzylic hydrogen by the respective chain radicals are in the ratio 1 3.5 6000. Chain transfer studies offer a convenient means for comparing radical reactivities, provided the absolute propagation constants also are known. 

Different initiators have varying transfer constants (Table 3-5). Further, the value of C) for a particular initiator also varies with the reactivity of the propagating radical. Thus there is a fivefold difference in C) for cumyl hydroperoxide toward poly(methyl methacrylate) radical compared to polystyryl radical. The latter is the less reactive radical see Sec. 6-3b. 

For example isopropylbenzene, which is considered as a model substance for polystyrene, has a chain transfer constant with polymethyl methacrylate radicals equal at 80° C to 1.9 10 4 (30). This means that at equimolecular concentration of monomer (methyl methacrylate) and transfer agent (isopropylbenzene, or in our case polystyrene) only one transfer reaction will occur against five thousand normal monomer addition steps. 

It is evident that the values of the transfer constants are dependent on the nature both of the attacking radicals and of the transfer agent itself, and that similar effects should be expected during the synthesis of graft copolymers by chain transfer methods. For example, with respect to toluene the chain transfer constant is a little greater for methyl methacrylate radicals than for styrene radicals on the contrary, with respect to halogenated solvents (CC14) the polystyrene radical is much more effective in the removal of a chlorine atom. Vinyl acetate chains are far more effective than either of the other two polymer radicals. 

On the other hand, with decreasing alkyl chain length separating the styrene (vinylbenzene) group from PEO the particle size increases. This was interpreted in terms of differences in rl (a reactivity parameter) values. It was assumed that the apparent reactivity of the macromonomer (1/rj) (characterizing the relative reactivity of the macromonomer towards poly(butyl methacrylate) radical) in... 

Organic radical battery — Group of rechargeable - batteries based on a redox couple with one organic radical, e.g., the poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) radical. 

The values of transfer constants directly indicate the danger of unfounded estimates of radical reactivities with respect to various substrates. The ratio of transfer rates of polystyrene and poly(methyl methacrylate) radicals to various substrates assumes a range of values [38] which are dependent on the substrate properties. The former radical is more reactive towards mercaptans, CBr4 or CC14, and the latter towards hydrocarbon transfer agents and trialkylamines which assume donor character in the transition complex. The interpretation of polar effects in macroradical reactivities is not yet satisfactory. 

Viscosity of the medium can also play a role in the kinetics due to the importance of diffusion in the observed rate constants. In the bulk radical polymerization of 2-phenoxyethyl methacrylate, thiol chain-transfer reagents operate at rates close to those observed for MMA while the rate of CCT catalyzed by 9a is an order of magnitude slower (2 x 103 at 60 °C) than that of MMA.5 The thiol reactions involve a chemically controlled hydrogen transfer event, whereas the reaction of methacrylate radicals with cobalt are diffusion controlled. The higher bulk viscosity of the 2-phenoxyethyl methacrylate has a significant influence on the transfer rate. 

The kp value for phenyl methacrylate (Table 7) is smaller than that for methyl methacrylate (Table 8), although phenyl methacrylate is more likely to be attacked by a free radical than methyl methacrylate (see copolymerization data96 97 ). Accordingly, it is clear that the propagating radical of methyl methacrylate is more reactive than that of phenyl methacrylate. This is because the phenyl methacrylate radical is more likely to form the radical-solvent complex, which is consistent with the above-mentioned proposal by Henrici-01iv6 et al.67-71 and Bamford et al.2 . 

Similarly, the variation of kp with solvent in methacrylate polymerization can be explained on the assumption that the complexed radical is either inactive or less reactive. Since methyl methacrylate has no aromatic ring in itself, it seems to be possible to estimate the stability constants for the complex formation of the poly (methyl methacrylate) radical end with aromatic solvents. However, since the variation of kp in methyl methacrylate polymerization with solvent is too small, the determination of Ks with significant figures is impossible. Accordingly, it is difficult to estimate the unpurturbed kpo value for methyl methacrylate and thus difficult to estimate the stability constant of the complex in aromatic solvents. 

Canadian researchers published two papers on the modeling of methyl methacrylate radical polymerization, which is characterized by a pronounced gel effect. 

PMMA methacrylate 2-dimethyl ammonium methyl methacrylate radical 167... 

Other water-borne coatings include water-soluble emulsions, dispersions, and latex resins. Water-soluble resins are rare because most resins derived from vegetable oils are insoluble in water. The true emulsions are based on the emulsification of the oil or alkyd through either the action of a surfactant or a resin that has a surfactantlike character. The alkyd emulsions are readily prepared and can be used for OEM coatings and architectural applications. The submicron size droplets are stabilized by the thickeners (El-Aasser Sudol, 2004 Landfester, 2005 Landfester et al., 2004 Tsavalas et al., 2004 Weissenborn Motiejauskaite, 2000a,b). In dispersions, the resin is a solid and is dispersed in water. The latex resin is usually vinyl acetate, styrene, acrylates, or methacrylates radically copolymerized in a micelle to form particles 0.1 pm in diameter (Bloom et al., 2005 Brister et al., 2000 Jiratumnukul Van De Mark, 2000 Thames et al., 2005). 

Ohtani, H., Tanaka, M., and Tsuge, S., Pyrol3 is-Gas Chromatographic Study of End Groups in Poly(methyl methacrylate) Radically Polymerized in Toluene Solution with Benzoyl Peroxide as Initiator, J. Anal Appl Pyrolysis, 15,167,1989. 

If more than one monomer species is present in the reaction medium, a copolymer or an interpolymer can result from the polymerization reaction. Whether, however, the reaction products will consist of copolymers or just mixtures of homopolymers or of both depends largely upon the reactivity of the monomers. A useful and a simplifying assumption in kinetic analyses of free-radical copolymerizations is that the reactivity of polymer radicals is governed entirely by the terminal monomer units. " For instance, a growing polymer radical, containing a methyl methacrylate terminal unit, is considered, in terms of reactivity, as a poly(methyl methacrylate) radical. This assumption, not always adequate, can be used to predict satisfactorily the behavior of many mixtures of monomers. Based on this assumption, the copolymerization of a pair of monomers involves four distinct growth reactions and two types of polymer radicals. 

The reaction, however, is not always strict inhibition. Thus, for instance, hydroquinone acts as an efficient inhibitor for the methyl methacrylate radical but only as a retarder for the styrene radical. Hydroquinone is often employed as an inhibitor, it requires, however, oxygen for activity ... 

Oxygen is less effective in inhibiting polymerizations of acrylic esters. It reacts 400 times faster with the methacrylic radicals than with the acrylic ones. Nevertheless, even small quantities of oxygen affect polymerization rates of acrylic esters. This includes photopolymerizations of gaseous ethyl acrylate that are affected by oxygen and by moisture. ... 

Active radicals (ethylene, acrylate, vinyl acetate) are more likely to abstract from a polymer chain than styrenic or methacrylate radicals, and acrylate and vinyl acetate monomer units on a chain are more likely to have an H-atom abstracted. Thus it is not uncommon for the overall transfer rate to decrease rapidly with increasing content of the less-reactive monomer. Similar issues must be examined when looking at cross transfer rates for chain transfer to monomer reactions [41]. 

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