Methyl methacrylate radical attack

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. 

Scheme 4.11. Addition of ethylene glycol dimethacrylate to a methyl methacrylate radical. The pendent double bond is attacked by another polymer radical to form a crosslink.

The presence of sulphonic and carboxylic groups enables the iron ions to be in the vicinity of the cellulose backbone chain. In this case, the radicals formed can easily attack the cellulose chain leading to the formation of a cellulose macroradical. Grafting of methyl methacrylate on tertiary aminized cotton using the bi-sulphite-hydrogen peroxide redox system was also investigated [58]. 

A radical cyclization of a 2-chloroacyl enamine 157 was used to synthesize 2-substituted pyroglutamates 160. Usually, the radical 158 undergoes an initial 5-endo cyclization (path a) and the resulting intermediate 159 attacked electrophiles like methyl acrylate to give the pyroglutamate 160. Unexpectedly, the reaction with methyl methacrylate took another course and a seven-membered... 

Another differential reaction is copolymerization. An equi-molar mixture of styrene and methyl methacrylate gives copolymers of different composition depending on the initiator. The radical chains started by benzoyl peroxide are 51 % polystyrene, the cationic chains from stannic chloride or boron trifluoride etherate are 100% polystyrene, and the anionic chains from sodium or potassium are more than 99 % polymethyl methacrylate.444 The radicals attack either monomer indiscriminately, the carbanions prefer methyl methacrylate and the carbonium ions prefer styrene. As can be seen from the data of Table XIV, the reactivity of a radical varies considerably with its structure, and it is worth considering whether this variability would be enough to make a radical derived from sodium or potassium give 99 % polymethyl methacrylate.446 If so, the alkali metal intitiated polymerization would not need to be a carbanionic chain reaction. However, the polymer initiated by triphenylmethyl sodium is also about 99% polymethyl methacrylate, whereas tert-butyl peroxide and >-chlorobenzoyl peroxide give 49 to 51 % styrene in the initial polymer.445... 

Radicals are soft most of them do not have a charge, and in most chemical reactions they react with uncharged molecules. Thus the Coulombic forces are usually small while the orbital interactions remain large. The clean polymerisation of methyl methacrylate demonstrates this typically soft pattern of behaviour. Radicals attack at the conjugate position of a,/3-unsaturated carbonyl compounds such as methyl methacrylate 7.1, rather than at the carbonyl group, and the attack... 

Clearly, the relative reactivity of a monomer does depend upon the nature of the radical that is attacking it. Maleic anhydride is much more reactive than stilbene toward radicals ending in a stilbene unit, and stilbene is much more reactive than maleic anhydride toward the other kind of radical. (Indeed, these two compounds, individually, undergo self-polymerization only with extreme dilhculty.) A more modest—and more typical- tendency toward alternation is shown by styrene and methyl methacrylate. Here, toward either radical (- M ) the opposite monomer (M2) is about twice as reactive as the same monomer (Mj). 

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 . 

Poly(methyl methacrylate) prepared by free radical polymerization is amorphous and is therefore soluble in solvents of similar solubility parameter. Effective solvents include aromatic hydrocarbons such as benzene and toluene chlorinated hydrocarbons such as chloroform and ethylene dichloride and esters such as ethyl acetate and amyl acetate. Some organic materials, although not solvents for the polymer, cause crazing and cracking, e.g., aliphatic alcohols and amines. Poly(methyl methacrylate) has very good resistance to attack by water, alkalis, aqueous inorganic salts and most dilute acids. Some dilute acids such as hydrocyanic and hydrofluoric acids, however, do attack the polymer, as do concentrated oxidizing acids. Poly(methyl methacrylate) has much better resistance to hydrolysis than poly(methyl acrylate), probably by virtue of the... 

Isotopic enhancement may be also illustrated by Bevington et al. s exploration of the use of the C-enriched free radical initiators 1,1 -azobis(phenylethane) and AIBN in preparing butadiene polymers [51] and the use of dimethyl 2,2 -azobis(isobutyrate) to initiate the polymerisations of styrene, acrylonitrile, methyl methacrylate and methyl acrylate [52]. The signals from the ends are thus rendered more intense, and b ome observable in a standard NMR spectrum, where they display information on the manner in which the initiator radicals have attacked the first monomer to become incorporated at the start of the polymer chain one can thus compare initial and mean tacticities. In a further use of isotope enrichment, Moad and Willing found that selective enrichment... 

Aromatic nitro compounds act as inhibitors and show greater tendency toward more reactive and electron-rich radicals. Nitro compounds have very little effect on methyl acrylate and methyl methacrylate [5,10,11] but inhibit vinyl acetate and retard styrene polymerization. The effectiveness increases with the number of nitro groups in the ring [1 13]. The mechanism of radical termination involves attack on both the aromatic ring and the nitro group. The reactions are represented as follows ... 

---