Polymerization metal methacrylates

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. 

Preparation and Reactions of S-b-MM. As mentioned in the introduction, we were interested in block copolymers of styrene and alkali metal methacrylates with overall molecular weights of about 20,000 and methacrylate contents on the order of 10 mol%. The preparation of such copolymers by the usual anionic techniques is not feasible. An alternative is to prepare block copolymers of styrene and methacrylic esters by sequential anionic polymerization, followed by a post-polymerization reaction to produce the desired block copolymers. The obvious first choice of methacrylic esters is methyl methacrylate. It is inexpensive, readily available, and its block copolymers with styrene are well-known. In fact, Brown and White have reported the preparation and hydrolyses of a series of S-b-MM copolymers of varying MM content using p-toluenesulfonic acid (TsOH) (6). The resulting methacrylic acid copolymers were easily converted to their sodium carboxylates by neutralization with sodium hydroxide. 

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... 

Many other metal-catalysed polymerizations may be carried out in water including the copper-catalysed polymerization of methacrylates, the palladium-and nickel-catalysed polymerization of ethene and other alkenes and the rhodium-catalysed polymerization of butadiene [22],... 

The last decades have witnessed the emergence of new living Vcontrolled polymerizations based on radical chemistry [81, 82]. Two main approaches have been investigated the first involves mediation of the free radical process by stable nitroxyl radicals, such as TEMPO while the second relies upon a Kharash-type reaction mediated by metal complexes such as copper(I) bromide ligated with 2,2 -bipyridine. In the latter case, the polymerization is initiated by alkyl halides or arenesulfonyl halides. Nitroxide-based initiators are efficient for styrene and styrene derivatives, while the metal-mediated polymerization system, the so called ATRP (Atom Transfer Radical Polymerization) seems the most robust since it can be successfully applied to the living Vcontrolled polymerization of styrenes, acrylates, methacrylates, acrylonitrile, and isobutene. Significantly, both TEMPO and metal-mediated polymerization systems allow molec-... 

The synthetic aspects of coordination catalysis still receive far more attention than mechanistic aspects, and precious little can be said with assurance concerning the mechanisms of the foregoing polymerization reactions. Almost the opposite is true of the free radical initiation of vinyl polymerization by metal carbonyls. Bamford et al. (10,11) have studied the kinetics of several such reactions and arrived at plausible interpretations of their results. The initiation of methyl methacrylate polymerization by tetracobalt dodecacarbonyl in the presence of carbon tetrachloride was studied in detail and the results were rationalized in terms of the following mechanism ... 

Inoue, Tsuruta, and Furukawa (30) found that metal ketyls polymerized acrylonitrile and methyl methacrylate, but not styrene. The lithium ketyls and dilithio complexes were not very active even in tetrahydrofuran. The disodio ketyl complex polymerized styrene quantitatively to give a living system. 

The rate of the thermally initiated methyl methacrylate polymerization amounts to only about 1 % of the rate measured with styrene. It can be increased by the presence of heavy metal atoms [16] which can change the multiplicity of the diradical and thus also its reactivity. 

A larger effect may, of course, be expected from a pulsed magnetic field, especially at high frequency, which could induce the valence electrons to vibrate. An indication of an effect generated by a pulsed field was described by Lambrev, who measured the catalytic efficiency of metal oxides (CdO, HgO, T1203, PbO, Br203) under the effect of such a field in methyl methacrylate polymerization [9], He observed activation and deactivation of the oxides which depended on the intensity of the pulsing field. 

Eppinger, J., Nikolaides, K.R., Zhang-Presse, M. et al. (2008) Alkyl complexes of rare-earth metal centers supported by chelating l,l -diamidoferrocene ligands synthesis, structure, and application in methacrylate polymerization. Organometallics, 27, 736. 

Polyethylene glycol in the synthesis of materials. PEG has been used as a solvent in polymerization reactions. It was found to facilitate easy removal of the metal catalyst in transition metal mediated living radical polymerization (Figure 8.10). Products from this type of polymerization are usually heavily contaminated with intensely coloured copper impurities. In the case of methyl methacrylate polymerization the reaction rate was higher than in conventional organic solvents, but for styrene the reaction was slower than in xylene. 

Better results were obtained in the methyl methacrylate polymerization reactions (Scheme 12). 153-156 showed high catalytic activity with a strong dependence on the ionic radius of the center metal. The lanthanum complex 154 was the most active catalyst and initiated the polymerization without any cocatalyst. Addition of small amounts of AlEts as cocatalyst increased the yield significantly. Polymerization initiated by 154 depended on the temperature and a low temperature (—78°C) was required to afford almost quantitative yields. The resulting polymers were basically syndiotactic and exhibited high molar masses and narrow polydispersities. The catalytic reaction with the lanthanum compound 157 showed no increase of catalytic activity but led to a larger fraction of atactic poly(methyl methacrylate). Moreover, the catalytic activity of all utilized initiators was solvent dependent. 153, 155, and 156 only showed catalytic activity by the addition of a cocatalyst. 153 afforded lower yield after changing the solvent from toluene into THF. 

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