Macroradical methyl methacrylate

Block copolymers of vinyl acetate with methyl methacrylate, acryflc acid, acrylonitrile, and vinyl pyrrohdinone have been prepared by copolymeriza tion in viscous conditions, with solvents that are poor solvents for the vinyl acetate macroradical (123). Similarly, the copolymeriza tion of vinyl acetate with methyl methacrylate is enhanced by the solvents acetonitrile and acetone and is decreased by propanol (124). Copolymers of vinyl acetate containing cycHc functional groups in the polymer chain have been prepared by copolymeriza tion of vinyl acetate with A/,A/-diaIlylcyanamide and W,W-diaIl5lamine (125,126). 

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]. 

Seymour and coworkers (27,28,29,30) actually used these composition gradients to prepare block copolymers by swelling particles containing occluded (i.e., living) macroradicals with a second monomer. Such block copolymers were prepared from occluded vinylacetate, methyl methacrylate, and acrylonitrile macroradicals, and the yield of block copolymers was studied as a function of the solubility and rate of diffusion of the swelling monomer in the particles. 

In this case, there are too few macroradicals available for reaction because of insufficient polymer degradation. In the disk-type extruder, a higher-stress gradient is achievable, more macroradicals are generated, and intensive cross-linking between polyethylene or highly chlorinated polyethylene and maleic anhydride or methyl methacrylate can be obtained (Heinicke 1984, Zhao et al. 2002, 2003). 

The mode of termination varies with monomer and reaction conditions. While styrene macroradicals typically terminate by coupling, methyl methacrylate macroradicals terminate by coupling at temperatures below 60°C, but by disproportionation at higher temperatures. 

Bischof (16) used the macroradicals resulting from vibromilling as initiators for synthesis of block and graft copolymers of poly(methyl methacrylate) with poly(vinyl chloride) with polyacrylonitrile. 

However, if increasing amounts of free radical acceptors are added to the system, the block and graft polymerization gradually decreases, as saturation of free macroradicals proceeds faster than the addition of monomers. In Table 2, the influence of benzoquinone on the graft polymerization of vinyl chloride on poly(methyl methacrylate) is shown (20). 

Poly (methyl methacrylate) was also subjected to mechanical reaction in a vibrating mill in common solvent for several monomers (ethylene, acrylic acid and its esters, acrylonitrile and styrene) at temperatures from —196 to 20° C (22). The formation of macroradicals and their reactions were followed by EPR (electron paramagnetic resonance). The macroradicals reacted with vinyl monomers at temperatures less than —100° C, while quinones underwent reaction as low as —196° C. The same experiments were performed also with polystyrene and polybutylenedimethacrylate. The radicals from polystyrene were more reactive than those from poly(methyl methacrylate). 

In the poly(methyl methaerylate)-styrene system, less than 7% of the original polymer remained as homopolymer at total conversion (77). Over 85% of the product was non-branched, single-segment block copolymer. The difference for these two systems is in part due to the higher molecular weight of the initial poiy(methyl methycrylate) (2900000 versus 495000) and in part to the preferential scission of the poly(methyl methacrylate) chain. This point was confirmed by running tests on a mixture of the two homopolymers in the presence of a radical acceptor to prevent macroradical recombination, and on the isolated block copolymers. 

Considering now reactions (5 a) and (5 b) (p. 176), it was found that the addition of monomers to macroradicals produced by chain transfer depends directly on the reactivity and polarity of both the radical and the monomer (203) and that the Q—e scheme of Alfrey and Price can be applied to these graft copolymerizations by chain transfer (227). In this way some unsuccessful attempts for grafting were interpreted, e. g. vinyl acetate on polystyrene and methyl methacrylate on polyvinyl acetate and polyvinyl chloride. 

The mechanical degradation and production of macroradicals can also be performed by mastication of polymers brought into a rubbery state by admixture with monomer several monomer-polymer systems were examined (10, 11). This technique was for instance studied for the cold mastication of natural rubber or butadiene copolymers in the presence of a vinyl monomer (13, 31, 52). The polymerization of methyl methacrylate or styrene during the mastication of natural rubber has yielded copolymers which remain soluble up to complete polymerization vinyl acetate, which could not produce graft copolymers by the chain transfer technique, failed also in this mastication procedure. Block and graft copolymers were also prepared by cross-addition of the macroradicals generated by the cold milling and mastication of mixtures of various elastomers and polymers, such as natural rubber/polymethyl methacrylate (74), natural rubber/butadiene-styrene rubbers (76) and even phenol-formaldehyde resin/nitrile rubber (125). 

Terminal air oxidation of polystyrene has recently been carried out by degradation of polystyrene in the presence of azo-bis-isobutyronitiile and air oxygen the polystyrene dihydroperoxide can initiate the polymerization of methyl methacrylate and acrylonitrile [193, 194). The yield of homopolymer is very low, indicating an exceptional difference of efficiency between the macroradical and the OH radical. 

Another polymer which is easily peroxidized is polyacetaldehyde it has a polyacetalic structure and is characterized by the presence of some side hydroperoxide groups (1 to 4°/00) due to traces of peracetic acid when the polymer is prepared. The homolytic decomposition of these peroxide groups yields macroradicals to which methyl methacrylate could be grafted [73, 74). 

Macroradicals obtained by the copolymerization of equimolar quantities of styrene and maleic anhydride in benzene or in cumene were also used as initiators to produce block copolymers with methyl methacrylate, ethyl methacrylate, and methyl acrylate. The yields of these block copolymers were less than those obtained with styrene, but as much as 38% of methyl methacrylate present in the benzene solution added to the macroradical to produce a block copolymer. The amount of ethyl methacrylate and methyl acrylate that was abstracted from the solution to form block copolymers was 35 and 20%. 

The formation of block copolymers from styrene-maleic anhydride and acrylic monomers was also indicated by pyrolytic gas chromatography and infrared spectroscopy. A comparison of the pyrograms of the block copolymers in Figure 7 shows peaks comparable with those obtained when mixtures of the acrylate polymers and poly(styrene-co-maleic anhydride) were pyrolyzed. A characteristic infrared spectrum was observed for the product obtained when macroradicals were added to a solution of methyl methacrylate in benzene. The characteristic bands for methyl methacrylate (MM) are noted on this spectogram in Figure 8. 

Norrish and Smith [29] and later Tromsdorff et al. [30] described a polymerization of methyl methacrylate, the rate of which increased from a certain conversion. The number of monomers of similar behaviour was extended by methyl acrylate [31 ], butyl acrylate [32] and other acrylates [33] and methacrylates [34], and vinyl acetate. The effect was explained by the reduction of the termination rate caused by hindered macroradical mobil-ity in viscous medium it was called the gel effect, or the Norrish-Tromsdorff effect. The gel effect is clearly manifested in radical polymerizations of weakly transferring monomers in bulk. It is significant also in the presence of a good solvent. The gel effect is suppressed by the presence of poor solvents++ and by... 

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. 

Arthur et al. reported that even in the presence of solvents in which cotton swells (HCL, dimethylformamide (DMFA) or dimethyl sulfoxide (DMSO)) about 30% of long-lived cellulose macroradicals resulting from irradiation were still unaccessible to the monomer. The same result was obtained from experiments25 involving grafting of methacrylate (MA) and methyl methacrylate (MMA) to cellulose in the presence of... 

Methyl methacrylate (Fig. 1-4) and methacrylonitrile (6-5) are allylic-type monomers that do yield high molecular weight polymers in free radical reactions. This is probably because the propagating radicals are conjugated with and stabilized to some extent by the ester and nitrile substituents. The macroradicals are... 

Styrene/methyl methacrylate (MMA) system was studied as a model (1 ). Styrene mainly terminates by combination. Homopolystyrene can be formed from the cleavage of an azo end-group. But the probability is low that two such macroradicals without an azo group will find each other. The fraction of homopolystyrene in this step is small. In the first step about 50% of the azo groups are decomposed this means a reaction time corresponding to one half-life of the initiator. 

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