Acrylonitrile macroradicals

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. 

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.

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. 

Good yields of acrylonitrile macroradicals were obtained when a benzene solution of this monomer was heated at 50°C with 2.5% AIBN. The difference between the solubility parameters of these macroradicals and styrene, 3.2 hildebrand units, was too great to permit diffusion of the styrene monomer in the acrylonitrile macroradical and therefore, no block copolymer was produced with this monomer. 

However, the difference between the solubility parameters of an equimolar mixture of styrene and maleic anhydride and the acrylonitrile macroradical is only 1.1 hildebrand units. Thus, a block copolymer with a ratio by weight of styrene and maleic anhydride to that of the acrylonitrile macroradical of 41/100 was obtained when a mixture of these... 

Block (or graft) copolymers have been obtained by the addition of styrene and N,N-dimethylformamide (DMF) to acrylonitrile macroradicals, and add by the addition of methyl methacrylate or styrene to vinyl chloride macroradicalsBlock copolymers have also been produced by the addition of various vinyl monomers to styrene-maleic anhydride macroradicals (122) ... 

PREPARATION OF BLOCK COPOLYMERS FROM STYRENE-ACRYLONITRILE MACRORADICALS... 

In this paper we will discuss evidence for the existence of CTC s of styrene and acrylonitrile and the resultant differences in the copolymer produced from them. We will also report the preparation of copolymers with block copolymer characteristics from poly(styrene-co-acrylonitrile) macroradicals prepared in tert-butyl alcohol. This solvent is a poor solvent for the macroradical and exhibits a very low chain transfer constant (28). The copolymers reported in this paper were prepared in the absence and presence of zinc chloride (ZnCU), and the effect of ZnClz on the reactivity of the macroradical will be discussed. 

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). 

Largest for glassy polymers like acrylonitrile which are not highly swollen by monomer. (Living macroradicals can be obtained in heterogeneous acrylonitrile polymerization.)... 

Ihe reaction of starch with oeric salts leads to formation of macroradicals vhich can initiate the polymerization of a wide variety of monomers to yield starch graft copolymers. Graft oopolymers of acrylonitrile and starch are easily prepared Icy technique (Equation 1), and se xxiif ication of starch-g-ipolyacry-lonitrile (Equation 2) yields absorbent polymers that can take jp... 

When a monomer such as acrylonitrile is polymerized in a poor solvent, macroradicals precipitate as they are formed. Since these are living polymers, polymerization continues as more acrylonitrile diffuses into the precipitated particles. This heterogeneous solution polymerization has been called precipitation polymerization. 

Many reactions have been performed in the presence of a solvent. However, the solvent must be chosen carefully to avoid reaction with polymer. For example, the low yield for grafts of acrylonitrile on polyamides in the presence of methanol has been shown to be due to the methanolysis (18,31). Generally speaking, the grafted products are principally obtained however minor amounts and homopolymers can also result. The homopolymerization proceeds by an intramolecular transfer reaction between macroradicals and monomers. The amount of homopolymer depends on the system. Details on systems already investigated will be described in the next section. 

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). 

For the case of acrylonitrile, there was an induction time of 24 h. This was attributed to the formation of cyanide radicals which are able to react with polyamidic macroradicals. The interpolymer is composed of two fractions one soluble in dimethyl formamide, whose properties are similar to polyacrylonitrile the other, insoluble in this solvent, whose properties are similar to those of the polyamide. No homopolymer was observed. The presence of acrylonitrile on the graft polymer was demonstrated by IR. 

Berlin and coworkers (5,56) desired to obtain a material with an increased mechanical strength. They carried out a plasticization of bulk ami emulsion polystyrene molecular weight 80000 and 200000 respectively at 150-160° C, with polyisobutylene, butyl rubber, polychloroprene, polybutadiene, styrene rubber (SKS-30) and nitrile rubber (SKN 18 and SKN 40). The best results were obtained with the blends polystyrene-styrene rubber and polystyrene-nitrile rubber. An increase of rubber content above 20-25% was not useful, as the strength properties were lowered. An increase in the content of the polar comonomer, acrylonitrile, prevents the reaction with polystyrene and decreases the probability of macroradical combination. This feature lowers the strength, see Fig. 14. It was also observed that certain dyes acts as macroradical acceptors, due to the mobile atoms of hydrogen of halogens in the dye, AX ... 

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. 

Relatively stable macroradicals are precipitated when they are insoluble in their monomers. Thus, poly (vinyl chloride) has been obtained by a process in which the solid polymer was removed continuously as it precipitated from the monomer (23). These precipitated macroradicals have been described as popcorn (21) or trapped free radicals (22). Macroradicals obtained by the polymerization of acrylonitrile which have been widely studied (4) have been used to prepare block copolymers (35). 

Since the partial insolubility of the starch-ceric ammonium nitrate reaction product complicates the interpretation of solubility data, we ran a second series of graft polymerizations using cobalt-60 as an initiator in an attempt to remove this variable (Table II). If combination of PAN macroradicals is occuring during graft polymerization, it should occur during cobalt-60 initiated polymerizations as well as in those initiated by ceric ammonium nitrate. In the first four reactions of Table II, starch was irradiated as a water slurry under graft polymerization conditions, but in the absence of acrylonitrile, to determine the influence of different doses of irradiation on starch solubility. 

Compound 35 contains a thermolabile C-C bond which, on thermally induced fragmentation, yields a high proportion of macroradicals. The PDMS diradical also acts as a counter radical and can undergo chain extension at both ends in the presence of vinylic monomers (acrylonitrile, maleic anhydride, diethylfumarate) or styrenic monomers, leading to diblock copolymers in 95% yield according to the following scheme [211, 212] ... 

Pichot et al. applied the spin-trapping technique to study the copolymerization of acrylonitrile with vinyl chloride or vinyl acetate [256]. Macroradicals terminated by the latter two units are trapped preferentially. The authors also noted suppression of cyclization by the spin-trapping agent cyclization is otherwise very common in acrylonitrile copolymerizations. 

Acrylonitrile polymerization at 25 °C in aqueous medium has been described 47,48). When ferric ions are present, some growing macroradicals are reduced with ferric ions ... 

The free-radical kinetics described in Chapter 6 hold for homogeneous systems. They will prevail in well-stirred bulk or solution polymerizations or in suspension polymerizations if the polymer is soluble in its monomer. Polystyrene suspension polymerization is an important commercial example of this reaction type. Suspension polymerizations of vinyl ehloride and of acrylonitrile are described by somewhat different kinetic schemes because the polymers precipitate in these cases. Emulsion polymerizations aie controlled by still different reaetion parameters because the growing macroradicals are isolated in small volume elements and because the free radieals which initiate the polymerization process are generated in the aqueous phase. The emulsion process is now used to make large tonnages of styrene-butadiene rubber (SBR), latex paints and adhesives, PVC paste polymers, and other produets. 

While it is assumed that termination by coupling takes place when maleic anhydride and styrene are copolymerized in a good solvent such as acetone, insoluble macroradicals precipitate when these monomers are copolymerized in a poor solvent such as benzene (7). Insoluble macroradicals obtained by bulk polymerization of acrylonitrile (1, 11) and the solution copolymerization of maleic anhydride and styrene in benzene (7) have been used as seeds for the preparation of block copolymers. 

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