Comonomer

White crystals m.p. 162-164 C. ll can be prepared by the fermentation of sugar with the mould Aspergillus lerreus or by healing citra-conic anhydride with water at ISO C. Electrolysis of the potassium salt in solution gives allene. Itaconic acid is used as a comonomer in plastics its esters are polymerized to lubricating oils and plasticizers. 

Irregularities such as branch points, comonomer units, and cross-links lead to amorphous polymers. They do not have true melting points but instead have glass transition temperatures at which the rigid and glasslike material becomes a viscous liquid as the temperature is raised. 

Copolymer. Acetal copolymers are prepared by copolymerization of 1,3,5-trioxane with small amounts of a comonomer. Carbon-carbon bonds are distributed randomly in the polymer chain. These carbon-carbon bonds help to stabilize the polymer against thermal, oxidative, and acidic attack. 

In a cross-linked polymer, the junction units are different kinds of monomers than the chain repeat units, so these molecules might be considered to be still another comonomer. While the chemical reactions which yield such cross-linked substances are copolymerizations, the products are described as cross-linked rather than as copolymers. In this instance, the behavior due to cross-linking takes precedence over the presence of an additional type of monomer in the structure. 

Comment on the likelihood that the comonomers are segregated as the names of these polymers suggest. 

Random copolymers tend to average the properties of the constituent monomers in proportion to the relative abundance of the two comonomers. 

Each diamond marks the intersection of two such rows and therefore corresponds to two comonomers. 

From the geometry of this triangular display, it follows immediately-if one overlooks the exceptions—that the more widely separated a pair of comonomers are in Fig. 7.2, the greater is their tendency toward alternation. Conversely the closer they are together, the greater their tendency toward randomness We recognize a parallel here to the notion that widely separated elements in the periodic table will produce more polar bonds than those which are closei together and vice versa. 

It is proposed to polymerize the vinyl group of the hemin molecule with other vinyl comonomers to prepare model compounds to be used in hemoglobin research. Considering hemin and styrene to be species 1 and 2, respectively, use the resonance concept to rank the reactivity ratios rj and X2. 

Another troublesome aspect of the reactivity ratios is the fact that they must be determined and reported as a pair. It would clearly simplify things if it were possible to specify one or two general parameters for each monomer which would correctly represent its contribution to all reactivity ratios. Combined with the analogous parameters for its comonomer, the values rj and t2 could then be evaluated. This situation parallels the standard potential of electrochemical cells which we are able to describe as the sum of potential contributions from each of the electrodes that comprise the cell. With x possible electrodes, there are x(x - l)/2 possible electrode combinations. If x = 50, there are 1225 possible cells, but these can be described by only 50 electrode potentials. A dramatic data reduction is accomplished by this device. Precisely the same proliferation of combinations exists for monomer combinations. It would simplify things if a method were available for data reduction such as that used in electrochemistry. 

The Price-Alfrey approach begins by defining three parameters-P, Q, and e-for each of the comonomers in a reaction system. We shall see presently that the parameter P is rapidly eliminated from the theory. As a result, the Price-Alfrey system is also called the Q-e scheme for copolymerization. 

In Chap. 4 we discussed the crystallizability of polymers and the importance of this property on the mechanical behavior of the bulk sample. Following the logic that leads to Eq. (4.17), the presence of a comonomer lowers T for a polymer. Carrying this further, we can compare a copolymer to an alloy in which each component lowers the melting point of the other until a minimummelting eutectic is produced. Similar trends exist in copolymers. 

Copolymers can be used to introduce a mixture of chemical functionalities into a polymer. Acidic and basic substituents can be introduced, for example, through comonomers like acrylic acid and vinyl pyridine. The resulting copolymers show interesting amphoteric behavior, reversing their charge in solution with changes of pH. 

Finally, the dielectric properties of a nonpolar polymer are modified by inclusion of even small amounts of a polar comonomer. In coatings applications the presence of polar repeat units in an otherwise nonpolar polymer reduces the tendency for static buildup during manufacture, printing, and ultimate use. On the other hand, in dielectric applications this increases the power loss and must be kept to a minimum, even to the exclusion of polar initiator fragments. 

Table 7.7 lists the common names and the comonomers for several addition copolymers that are widely used as elastomers, fibers, or films. 

Styrene and methyl methacylate have been used as comonomers in many investigations of copolymerization. Use the following listj of ri values for each of these copolymerizing with the monomers listed below to rank the latter with respect to reactivity ... 

Use the Q and e values listed in Table 7.4 for each of the comonomers to give five independent estimates of Q and e for acrylonitrile. Compare the average of these four with the values given for acrylonitrile in Table 7.4. 

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