Monomer styrene-acrylonitrile copolymerization

In the case of vinyl monomers (styrene, acrylonitrile, acrlylamide, isobutylene, etc.) copolymerization is generally spontaneous however, the reaction products are determined by the kinetic constants - a case of interplay between thermodynamic and kinetic factors. 

Table II - Styrene-Acrylonitrile copolymerization in batch - Effect of monomer initial concentration...

Styrene-acrylonitrile copolymerization in a semi-batch reactor Two cases (a) maximization of monomer conversion and minimization of polydispersity index at the end of reaction, and (b) maximization of monomer conversion at the end of reaction while minimizing polydispersity index at the end of reaction and molar ratio of unreacted monomer in the reactor at any time. NSGA-11 The decision variables for optimization were trajectories of addition rate of a monomer-solvent-initiator mixture and reactor temperature. Nayak and Gupta (2004)... 

In all manufacturing processes, grafting is achieved by the free-radical copolymerization of styrene and acrylonitrile monomers in the presence of an elastomer. Ungrafted styrene—acrylonitrile copolymer is formed during graft polymerization and/or added afterward. 

In studies of the polymerization kinetics of triaUyl citrate [6299-73-6] the cyclization constant was found to be intermediate between that of diaUyl succinate and DAP (86). Copolymerization reactivity ratios with vinyl monomers have been reported (87). At 60°C with benzoyl peroxide as initiator, triaUyl citrate retards polymerization of styrene, acrylonitrile, vinyl choloride, and vinyl acetate. Properties of polyfunctional aUyl esters are given in Table 7 some of these esters have sharp odors and cause skin irritation. 

Styrene readily copolymerizes with many other monomers spontaneously. The styrene double bond is electronegative on account of the donating effect of the phenyl ring. Monomers that have electron-withdrawiag substituents, eg, acrylonitrile and maleic anhydride, tend to copolymerize most readily with styrene because their electropositive double bonds are attached to the electronegative styrene double bond. Spontaneous copolymerization experiments of many different monomer pair combiaations iadicate that the mechanism of initiation changes with the relative electronegativity difference between the monomer pairs (185). 

When a polymerization uses two or more different types of monomers, it is called copolymerization. Examples are styrene acrylonitrile, LLDPE (ethylene and butenerl), and polyester (ethylene glycol and maleic anhydride). 

Copolymerization allows the synthesis of an almost unlimited number of different products by variations in the nature and relative amounts of the two monomer units in the copolymer product. A prime example of the versatility of the copolymerization process is the case of polystyrene. More than 11 billion pounds per year of polystyrene products are produced annually in the United States. Only about one-third of the total is styrene homopolymer. Polystyrene is a brittle plastic with low impact strength and low solvent resistance (Sec. 3-14b). Copolymerization as well as blending greatly increase the usefulness of polystyrene. Styrene copolymers and blends of copolymers are useful not only as plastics but also as elastomers. Thus copolymerization of styrene with acrylonitrile leads to increased impact and solvent resistance, while copolymerization with 1,3-butadiene leads to elastomeric properties. Combinations of styrene, acrylonitrile, and 1,3-butadiene improve all three properties simultaneously. This and other technological applications of copolymerization are discussed further in Sec. 6-8. 

Although the reactivity of 1,2-disubstituted ethylenes in copolymerization is low, it is still much greater than their reactivity in homopolymerization. It was observed in Sec. 3-9b-3 that the steric hinderance between a P-substituent on the attacking radical and a substituent on the monomer is responsible for the inability of 1,2-disubstituted ethylenes to homopolymerize. The reactivity of 1,2-disubstituted ethylenes toward copolymerization is due to the lack of P-substituents on the attacking radicals (e.g., the styrene, acrylonitrile, and vinyl acetate radicals). 

COPOLYMERIZATION WITH PARTICIPATION OF MULTIMONOMERS Synthesis of various multimonomers and their copolymerization with styrene, acrylonitrile or acrylic acid was described in a set of papers. Most of the early work on the copolymerization of multimonomers with vinyl monomers employed p-cresyl formaldehyde resins, esterified by methacryloyl chloride or acryloyl chloride, as one of the comonomers, and a simple vinyl monomer such as styrene or acrylonitrile as the other monomer. 

Acrylonitrile copolymerizes readily with many electron-donor monomers oilier than styrene. Hundreds of acrylonitnle copolymers have been reported, and a comprehensive listing of reactivity ratios for acrylonitrile copolymerizations is readily available. 

The concept of PO macroinitiators centers on the introduction of an initiation moiety into an olefinic polymer chain for polymerization. The most effective route for preparing PO macroinitiators is by employing functional polyolefins containing hydroxyl groups or other reactive groups. These functional POs are prepared by copolymerization of olefins with functional monomers and post-polymerization reaction, as mentioned above. In the case where an initiation moiety was at the chain-end of the polyolefins, a block type copolymer is produced. It has been reported that thiol-terminated PP was used as polymeric chain transfer agent in styrene and styrene/acrylonitrile polymerization to form polypropylene-b/odc-polystyrene (PP-b-PS) and polypropylene-btock-poly(styrene-co-acrylonitrile) (PP-b-SAN) block copolymer [19]. On the other hand, polymer hybrids with block and graft structures can be produced if initiation moieties are in the polymer chain. 

We have just discussed several methods for improving the mechanical properties of polymers. In addition to these techniques, one could think about synthesizing copolymers of styrene and less brittle monomer(s). Actually, we have already seen that this approach has been used with considerable success (see Chapter 5 and Table 5-2). Styrene-acrylonitrile (SAN) copolymers and acrylonitrile-butadiene-styrene (ABS) terpolymers have excellent impact strength. Although sometimes copolymerization is a viable option, oftentimes a completely different approach is called for. Let s see how. 

Wettability of Elastomers and Copolymers. The wettability of elastomers (37, 38) in terms of critical surface tension was reported previously. The elastomers commonly used for the reinforcement of brittle polymers are polybutadiene, styrene-butadiene random and block copolymers, and butadiene-acrylonitrile rubber. Critical surface tensions for several typical elastomers are 31 dyne/cm. for "Diene rubber, 33 dyne/cm. for both GR-S1006 rubber and styrene-butadiene block copolymer (25 75) and 37 dyne/cm. for butadiene-acrylonitrile rubber, ( Paracril BJLT nitrile rubber). The copolymerization of butadiene with a relatively polar monomer—e.g., styrene or acrylonitrile—generally results in an increase in critical surface tension. The increase in polarity is also reflected in the increase in the solubility parameter (34,39, 40) and in the increase of glass temperature (40). We also noted a similar increase in critical surface tensions of styrene-acrylonitrile copolymers with the... 

Acrylonitrile copolymerizes readily with many electron-donor monomers other than styrene. Hundreds of acrylonitrile copolymers have been reported, and a comprehensive listing of reactivity ratios for acrylonitrile copolymerizations is readily available (34,102). Copolymerization mitigates the undesirable properties of acrylonitrile liomopolymer, such as poor thermal stability and poor processability. At the same time, desirable attributes such as rigidity, chemical resistance, and excellent barrier properties are incorporated into melt-processable resins. 

In general, an alternating eopolymer is formed over a wide range of monomer compositions. It has been reported that little chain transfer occurs, and in some cases, conventional free radical retarders are ineffective. Reaction occurs with some combinations, like styrene-acrylonitrile, when the monomers are mixed with a Lewis acid, but addition of a free-radical source will increase the rate of polymerization without changing the alternating nature of the copolymer. Alternating copolymerizations can also be initialed photochemically and electrochemically. The copolymerization is often accompanied by a cationic polymerization of the donor monomer. 

Rank the following monomers in order of their increased tendency to alternate in copolymerization with butadiene and explain your reasoning vinyl acetate, styrene, acrylonitrile, and methyl methacrylate, Hint Use Q-e values if reactivity ratios are not readily available.)... 

Another aspect of free radical polymerizations under pressure which has been recently studied is the effect of pressure on comonomer reactivity ratios (5). In two copolymerization systems—styrene-acrylonitrile and methyl methacrylate-acrylonitrile—it was found that the product of the reactivity ratios, rif2, approaches unity as the pressure is increased. The monomer-polymer composition curves for these two copolymerizations at 1 and 1000 atm. are illustrated in Figures 1 and 2. The effect of pressure on the individual reactivity ratios and on the fit2 product is given in Table II. 

Bulk addition multipolymerization kinetics occurs when two monomers are employed. Bulk free-radical homopolymerizations and copolymerizations that are implemented in REX include a) styrene-acrylonitrile, styrene-methyl methacrylate, styrene-acrylamide b) methyl methacrylate-acrylonitrile, ABS c) acrylate ester mixtures d) ethyl acrylate-methacrylic acid and mixtures with other monomers e) methyl methacrylate f) 8-caprolactone and, n-isopropylacrylamide-acrylic... 

The rates of radical-monomer reactions are also dependent on considerations of steric effects. It is observed that most common 1,1-disubstituted monomers — for example, isobutylene, methyl methacrylate and methacrylo-nitrile—react quite readily in both homo- and copolymerizations. On the other hand, 1,2-disubstituted vinyl monomers exhibit a reluctance to ho-mopolymerize, but they do, however, add quite readily to monosubstituted, and perhaps 1,1-disubstituted monomers. A well-known example is styrene (Ml) and maleic anhydride (M2), which copolymerize with r — 0.01 and T2 = 0 at 60°C, forming a 50/50 alternating copolymer over a wide range of monomer feed compositions. This behavior seems to be a consequence of steric hindrance. Calculation of A i2 values for the reactions of various chloroethylenes with radicals of monosubstituted monomers such as styrene, acrylonitrile, and vinyl acetate shows that the effect of a second substituent on monomer reactivity is approximately additive when both substituents are in the 1- or cr-position, but a second substituent when in the 2- or /3-position of the monomer results in a decrease in reactivity due to steric hindrance between it and the polymer radical to which it is adding. 

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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