Styrene acrylonitrile monomer units

The sequence distribution of the styrene and acrylonitrile monomer units in SAN copolymers can be determined by, 3C NMR spectroscopy, and the experimental... 

A commercially important example of the special case where one monomer is the same in both copolymers is blends of styrene—acrylonitrile, 1 + 2, or SAN copolymers with styrene—maleic anhydride, 1 + 3, or SMA copolymers. The SAN and SMA copolymers are miscible (128,133,144) so long as the fractions of AN and MA are neatly matched, as shown in Figure 4. This suggests that miscibility is caused by a weak exothermic interaction between AN and MA units (128,133) since miscibility by intramolecular repulsion occurs in regions where 02 7 can be shown (143) by equation 11. 

The molecules join together to form a long chain-like molecule which may contain many thousands of ethylene units. Such a molecule is referred to as a polymer, in this case polyethylene, whilst in this context ethylene is referred to as a monomer. Styrene, propylene, vinyl chloride, vinyl acetate and methyl methacrylate are other examples of monomers which can polymerise in this way. Sometimes two monomers may be reacted together so that residues of both are to be found in the same chain. Such materials are known as copolymers and are exemplified by ethylene-vinyl acetate copolymers and styrene-acrylonitrile copolymers. 

ABS resin (acrylonitrile-butadiene-styrene) is an example of a random copolymer with three different monomer units, not necessarily present in the same amount. 

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. 

ABS is short for poly(acrylonitrile-butadiene-styrene) and this is a copolymer, so called because it is made from a mixture of basic monomer units, each of which bring some desirable property to the final product. ABS is widely used to make children s toys, car facias, and fingernail extensions. 

The amount of polymer formed in the solution phase must also be greatly restricted. Even assuming that all of the radicals are generated in the solution phase, they become insoluble after adding only perhaps five or 10 monomer units (23). Precipitation should occur rapidly on existing nuclei such as the surface of already precipitated polymer. Hence, the large surface of the particle constitutes an efficient radical trap which maintains the concentration of radicals in the solution phase at a very low level. The situation is comparable with that in emulsion polymerization. An analysis similar to that of Smith (27) for the emulsion polymerization of styrene shows that the average lifetime of a radical in the solution phase is sufficient to add only one to 10 acrylonitrile units before the radical collides with a polymer particle. 

ABS plastic is a tough, hard plastic used in applications requiring shock resistance. (See Chapter 22.) The polymer consists of three monomer units acrylonitrile (C3H3N), butadiene (C4H6), and styrene (QHs). 

The UV absorption in the 260 nm region is frequently used to evaluate styrene content in styrene-based polymers (2, 2, 3, 4, 5, 6, 7). Calibration curves for polystyrene solutions are usually based on the assumptions that the UV absorption of the copolymer depends only on the total concentration of phenyl rings, and the same linear relationship between optical density and styrene concentration that is valid for polystyrene holds also for its copolymers. These assumptions are quite often incorrect and have caused sizable errors in the analysis of several statistical copolymers. For example, anomalous patterns of UV spectra are given by random copolymers of styrene and acrylonitrile (8), styrene and butadiene (8), styrene and maleic anhydride (8), and styrene and methyl methacrylate (9, 10, 11). Indeed, the co-monomer unit can exert a marked influence on the position of the band maxima and/or the extinction... 

The use of dye-sensitized initiation in polymerization dates to 1949 when Bamford and Dewar observed that some vat dyes could sensitize the photopolymerization of styrene. This was quickly followed up hy Gerald Oster s discovery " in 1954 that the polymerization of acrylonitrile and of acrylamide could be photoinitiated by fluorescein, rose bengal, and similar dyes, in the presence of reducing agents (such as phenylhydrazine, ascorbic acid) and oxygen. Remarkably, the amount of dye required for the photoinitiation event was extremely small ( 0.1% of the weight of monomer), and the quantum yield of monomer consumption was in excess of 4000 monomer units per photon. " ... 

The polymer consists of three monomer units acrylonitrile (C3H3N), butadiene (C4Hg), and styrene (CsHs). 

In this chapter we discuss PVT and surface properties of three sets of random copolymers. Monomer units are ethylene, vinyl alcohol, and vinyl acetate, as well as styrene and acrylonitrile. Random copolymers comprising these monomers are used widely. As an example, ethylene-vinyl alcohol random copolymers (EVOHs) have excellent gas barrier properties. They are used for food-packaging films or in fuel tank liners [Takahashi et al., 1999 Alvarez et al., 2003 Ito et al., 2003 Lopez-Rubio et al., 2003 Muramatsu et al. 2003]. 

Nevertheless, many elastomers and plastics are fundamentally very similar. Most plastics and elastomers comprise long chains of one or more types of linked monomer units. In fact, many of the same monomers are found in both thermoplastic and elastomeric polymers—e.g., styrene, acrylonitrile, ethylene, propylene, and acrylate esters. Because of the chemical similarities between elastomers and plastics, these materials are susceptible to many of the same types of chemical attack. Therefore, many of the same material-selection principles come into play for both plastics and elastomers. 

There are many different types of polymers. In addition to the linear polymers such as polyethylene, there are branched polymers and cross-linked polymers. Copolymers can be prepared by polymerizing one alkene in the presence of another. When styrene and acrylonitrile are polymerized in the same reaction vessel, for example, a copolymer such as 177 is formed. These copolymers can be random copolymers, where there is no deflnite sequence of monomer units, but they can also be regular copolymers, where there is a regular alternating sequence of each monomeric unit. 

Intramolecular Repulsive Interactions. Miscible blends can also be achieved in absence of specific interactions, by exploiting the so-called intramolecular repulsive effect. This is observed in mixtures where at least one of the components is a statistical copolymer miscibility is restricted to a miscibility window, that is, it takes place within a well-defined range of copolymer composition. For example, poly(styrene-co-acrylonitrile) (SAN) and poly(methyl methacrylate) form miscible blends for copolymer compositions in the range 9-39% acrylonitrile (26,27). Miscibility in these systems is not a result of specific interactions but it is due to the intramolecular repulsive effect (28) between the two monomer units in the copol5uner such that, by mixing with a third component, these imfavorable contacts are minimized. The same situation is encoimtered in binary mixtures of two copol5uners (29). 

S=Nh /, =mean number of monomer units per chain, a=numerical factor, of order unity, dependent on character of bonds. If U is taken as bond dissociation energy, y is estimated within a factor of two of values deduced from experiments on isoprene, and butadiene-styrene, and acrylonitrile-butadiene copolymers. 

Sometimes, it occurs that the Fineman-Ross plot shows that experiments do not fit the theoretical straight line corresponding to a penultimate effect in the extreme range of composition of monomer feed. This fact might indicate the influence of the more remote units. For instance, such an occurence is encountered when copolymerizing styrene-acrylonitrile and vinyl chloride-vinyl acetate systems. Calculations analogous to those mentionned above may be performed with the equation proposed by G. E. Ham [7] for pen-penultimate effects, which allows the determination of the reactivity ratios (with adjunction of some more assumptions). We performed these types of calculation for the two systems for... 

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