Macroradical acrylic

Carboxylated polymers can be prepared by mechanical treatment of frozen polymer solutions in acrylic acid (Heinicke 1984). The reaction mechanism is based on the initiation of polymerization of the frozen monomer by free macroradicals formed during mechanolysis of the starting polymer. Depending on the type of polymer, mixed, grafted, and block polymers with a linear or spatial structure are obtained. What is important is that the solid-phase reaction runs with a relatively high rate. For instance, in the polyamide reactive system with acrylic acid, the tribochemical reaction leading to the copolymer is completed after a treatment time of 60 s. As a rule, the mechanical activation of polymers is mainly carried out in a dry state, because the structural imperfections appear most likely here. 

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). 

Copolymers. Vinyl acetate copolymenzes easily with a few monomers, e g, ethylene, vinyl chloride, and vinyl neodecanoate, which have reactivity ratios close to its own. Block copolymers of vinyl acetate with methyl methacrylate, acrylic acid, acrylonitrile, and vinyl pyrrolidinone have been prepared by copolymerization in viscous conditions, with solvents that are poor solvents for the vinyl acetate macroradical,... 

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. 

I. Formation of macroradicals. Radiat Phys Chem 46 913-916 Ulanski P, Bothe E, Flildenbrand K, Rosiak JM, von Sonntag C (1996a) Flydroxyl-radical-induced reactions of poly(acrylic acid) a pulse radiolysis, EPR and product study, part II. Oxygenated solution. J Chem Soc Perkin Trans 2 23-28... 

Fig. 3. Reactivity of monomers with n-n conjugation (1) with styrene macroradical, (2) with acrylonitrile macroradical (points with vanes). O, MM A , methyl vinyl ketone , acrolein 3, butyl acrylate, AN methyl acrylate Q acrylamine < > methacrylonitrile.

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... 

New macroradicals have been obtained by proper solvent selection for the homopolymerization of styrene, methyl methacrylate, ethyl acrylate, acrylonitrile, and vinyl acetate, and by the copolymerization of maleic anhydride with vinyl acetate, vinyl isobutyl ether, or methyl methacrylate. These macroradicals and those prepared by the addition to them of other monomers were stable provided they were insoluble in the solvent. Since it does not add to maleic anhydride chain ends, acrylonitrile formed a block copolymer with only half of the styrene-maleic anhydride macroradicals. However, this monomer gave excellent yields of block polymer when it was added to a macroradical obtained by the addition of limited quantities of styrene to the original macroradical. Because of poor diffusion, styrene did not add to acrylonitrile macroradicals, but block copolymers formed when an equimolar mixture of styrene and maleic anhydride was added. 

Macroradicals were obtained by the polymerization of ethyl acrylate in cyclohexane, styrene in hexane, vinyl acetate in decane, and methyl methacrylate in hexane. Because of the solubility of the vinyl acetate block in hexane, the ratio of the weight of vinyl acetate to that of the macroradical in poly (methyl methacrylate-b-vinyl acetate) after heating at 50°C for three days was only 30/100. By contrast, because of the insolubility of the acrylonitrile block in hexane, good yields of methyl methacrylate-b-acrylonitrile macroradicals were obtained. The ratio of the weight of the acrylonitrile block to that of the macroradical was thus 90/100 after heating the mixture for three days at 50°C in hexane. 

As prepolymers used in crosslinking reactions of acrylic enamels are usually copolymers of acrylic (x = H) and methacrylic (x = CH ) type monomers, the macroradical I can undergo a number of rearrangements depending on the local sequence distribution. For X = Y = CH3 (a methacrylate sequence) one obtains ... 

The temperature at which a dynamic equilibrium is reached between the formation and the decay of monomer macroradicals is called a ceiling temperature. For certain monomers, there are published ceihng temperatures, heats, and entropy of polymerization (28,29). Their values are, for example, 150°C for MAH, 200°C for methacrylate, 400°C for acrylate and styrene (28). It should be noted that these values are typical of reactions occurring at a constant (atmospheric) pressure and monomer concentration (usually 1 mol). The peak temperature rises with monomer concentration and pressure. That is why MAH was observed to homopolymerize at an extrusion temperature above 160°C (30). 

The rate of polymerization increases in this series of metals Mg(II) < Sr(II) < Ba(II) < Ca(II), The nature of the cation is likely to have a significant effect on the kinetics of the polymerization of salts of unsaturated acids in ionizing environments [68-70]. These differences are attributed to a different charge density at the macroradical anion, which influences the rate of interaction in the propagating macroradical-monomeric anion system. In comparable conditions the rate of radical polymerization of transition metal acrylates is lower than that of acrylic acid (AA) and decreases in the series (Fig. 4-7) [71] AA > Co(II) > Ni(II) > Fe(III) > Cu(II) (see Experiment 4-1, Section 4.6). The resulting metallopolymers are insoluble in any organic solvent, which indicates... 

Interestingly, polyacrylonitrile, poly (methyl acrylate), and polystyrene behave differently in the rigid state and in dilute solution. This may be explained in terms of lateral macroradicals being generated upon the release of side groups in a primary step. The combination of these radicals competes with decomposition through main-chain rupture. In dilute solution, where radical encounters are much less probable than in the rigid state, main-chain rupture predomi-... 

When acrylic acid or vinylpyrrolidone was heated with a precipitated acrylonitrile polymer believed to contain macroradicals, block like polymers were formedLikewise poly(acrylonitrile-b-methyl methacrylate) was reportedly produced when acrylonitrile was heated with precipitated methyl methacrylate polymer. Acrylonitrile-styrene copolymers however, were formed only when styrene and acrylonitrile precipitated polymer were heated in the presence of DMF. Presumably the DMF swells the polyacrylonitrile permitting diffusion of styrene monomer into the free radical containing coils. Block copol3miers of methyl methacrylate and various vinyl monomers have also been reported prepared by heating monomers and methyl methacrylate macroradicals in l-propanol(126). Interestingly poly-... 

In a similar preparation styrene macroradicals have been reported when styrene was polymerized in viscous solvents and viscous poor solvents(130). When styrene was added to these macroradicals, an increase in relative viscosity was noted. Block like copolymers were formed when either acrylonitrile, methyl methacrylate, ethyl acrylate or methacrylate was added to the macroradicals. The fastest rates of polymerization and greatest yields of copolymer were noted when polystyrene was pol37merized in viscous, poor solvent (131). ... 

The evolving molecules of HCl can react with macromolecules or macroradicals of the other components of blends, which can lead to a destabilization as well as to a stabilization of the blends. The presence of PVC in a blend induces destabilization, and then a more rapid degradation, in other polymers such as poly (vinyl acetate) (PVA). In its turn, its degradation rate increases in the presence of PVA, polyacrylamide (PAM), polyacrylonitrile (PAN), chlorinated rubber, etc. On the contrary, in a few cases, stabilization to some extent is achieved by PVC blended with PAN and some acrylic polymers. 

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