Copolymerization, azeotropic

The heterogeneous copolymerization of styrene and acrylonitrile in various diluents as reported by Riess and Desvalois (22). Although the copolymer composition in these studies was not strongly influenced by the diluent choice, the preferential adsorption of acrylonitrile monomer onto the polymer particles shifted the azeotropic copolymerization point from the 38 mole % acrylonitrile observed in solution to 55 mole % acrylonitrile. 

If equimolar quantities of Mi and M2 are used in an azeotropic copolymerization, what is the composition of the feed after 50% of the copolymer has formed ... 

The plots in Fig. 6-2 illustrate an interesting characteristic of copolymerizations with a tendency toward alternation. For values of r and r2 both less than unity, the F /f plots cross the line representing F — j. At these interesections or crossover points the copolymer and feed compositions are the same and copolymerization occurs without a change in the feed composition. Such copolymerizations are termed azeotropic copolymerizations. The condition under which azeotropic copolymerization occurs, obtained by combination of Eq. 6-12 with d[Mi]/ii[M2] = [Mi]/[M2], is... 

Corresponding data for the alternating radical copolymerization of styrene (Mi)-diethyl fumarate (M2)(n = 0.30 and r2 = 0.07) are shown in Figs. 6-6 and 6-7. This system undergoes azeotropic copolymerization at 57 mol% styrene. Feed compositions near the azeotrope yield narrow distributions of copolymer composition except at high conversion where there is a drift to pure styrene or pure fumarate depending on whether the initial feed contains more or less than 57 mol% styrene. The distribution of copolymer compositions becomes progressively wider as the initial feed composition differs more from the azeotropic composition. 

Radical Copolymerization of Styrene with Acryionitriie (Azeotropic Copolymerization)... 

This model shows that the radius of polymer particle follows simple scaling relationships with the key parameters in the system x1/3, [comonomer]02/3, [macromonomer]01/2, and [initiator]0 1/2, where [ ]0 means initial concentration. These equations also predict that the particle size and stabilization are determined by the magnitude of In addition the surface area occupied by a hydrophilic (PEO) chain follows x 1/3 in the case of azeotropic copolymerization, x=Xj. This means that the PEO chain conformation for chains grafted onto the polymer particles change with grafting density. 

Comparing the reactivity ratios of the DADMAC/AAM copolymerization with results of the copolymerization of other cationic monomers with AAM, significant differences can be identified. The differences between rx and r2 are much lower, and the cationic monomer even reacts preferentially during the copolymerization. As an example, for cationic methacrylic esters and methacrylamid derivatives, 1 nonideal copolymerization preferring the cationic component. For the cationic analogs of acrylic acid and acrylamide, 0.34azeotropic copolymerization, preferring the cationic monomer only at low content in the comonomer mixture. 

Except in very special cases (azeotropic copolymerizations), copolymerization via radical mechanism shows a drift in the composition of the copolymers produced through the polymerization process. Emulsion copolymerization obeys this rule too, although the special features of its mechanism can change the drift process. The most common way to obviate that composition drift is to use the semi-continuous process where, after polymerization has been initiated with a small percent of the total charge (say 10 to 20 %) like in the batch process, most of the charge is added continuously at a much smaller rate (Ra) than the rate (Rp) at the end of the batch period, so that the added charge is polymerized quite instantaneously (J, 2). Then,the composition drift is limited to the initial period and most of the product does possess actually a constant composition. 

Even in the first publications concerning the copolymerization theory [11, 12] their authors noticed a certain similarity between the processes of copolymerization and distillation of binary liquid mixtures since both of them are described by the same Lord Rayleigh s equations. The origin of the term azeotropic copolymerization comes just from this similarity, when the copolymer composition coincides with monomer feed composition and does not drift with conversion. Many years later the formal similarity in the mathematical description of copolymerization and distillation processes was used again in [13], the authors of which, for the first time, classified the processes of terpolymerization from the viewpoint of their dynamics. The principles on which such a classification for any monomer number m is based are presented in Sect. 5, where there is also demonstrated how these principles can be used for the copolymerization when m = 3 and m = 4. 

Because [M,]/[M2] > 0, both parameters must be smaller (or larger) than 1 in this case, which is called azeotropic copolymerization. The situation represented by eqn. (77) is fairly frequent. 

Reactivity ratios of isobutylene and -pinene have been determined. The product of reactivity ratios is approximately unity and, interestingly, rp decreases while rj increases with decreasing temperatures in the range from -50 to -1 lO". The plot of the logarithm of reactivity ratios versus the reciprocal temperature gave a straight line, the slope and intercept of which yielded the difference of enthalpy and entropy of activation (Fig. 8). Thus, 0-pinene is more reactive in terms of privation entropy and isobutylene is more reactive in terms of activation enthalpy. Significantly, below —100 both reactivity ratios become equal to unity, ie., azeotropic copolymerization prevails. 

As seen from Figure 2.3.2, the composition of the polymer and that of the feed is usually different. As the reaction progresses, only by maintaining a constant composition of the feed is it possible to obtain a uniform copolymer. For rA and re less than unity, the variation of Fa as a function of fa has a point where (Fa)c = (fA)c. where the composition of the copolymer is identical to the concentration of the feed. The copolymerization at this concentration is known as azeotropic copolymerization. This is achieved when fA has the value given by rel. (2.3.24) ... 

Note that Table 1.13 also includes the special case rj =r2= 1, for which F ] =/i and F 2 =f2- Another condition for such azeotropic copolymerization in which the copolymer composition is equal to the feed composition is when/j// = (r2 — V)l r — 1). The desimble range of rj to produce copolymers with a reasonable range of both monomers present is from 0.5 to 2. 

Figure 7.2 shows curves for several nonideal cases, that is, where r T2 1. It is seen that when both r and T2 are less than 1 there exists some point on the i i-versus-/i curve where the copolymer composition equals the feed composition and at this point the curve crosses the line F = f (that is, the diagonal line). At this point of intersection, polymerization proceeds without change in either feed or copolymer composition. Distillation terminology is again borrowed for this instance. Azeotropic copolymerization is said to occur at such points and the resulting copolymers are called azeotropic copolymers. 

Figure 3). This monomer pair had an azeotropic copolymerization composition at ca. 26 mole % DHA. 

In the hypothetical case when fi = t2 = 1, none of the two macroradicals differentiates between the monomers, and the composition of the copolymer equals that of the monomer mixture at any degree of conversion (the so-caUed azeotropic mixture of comonomers). Only in this particular case (line 5) is the distribution of the monomers in the macromolecule formed close to statistical. When q < 1 and f2 < 1, radical —m tends to react with monomer M2, whereas radical — reacts more rapidly with monomer Mj. This tendency to alternation of the monomer units mi and m2 in the growing chain results, among others, in the predominant consumption of the minor component at the beginning of copolymerization (plot 3). The deviation from azeotropic copolymerization is also pronounced in the case of = T2 < 1 (plot 4). However, if the starting mixture contains both comonomers in equal... 

In those cases, where rj and V2 both either less or greater than unity, the curves of Figure 8.2 cross the line Fj = fj. The points of interception represent the occurrence of azeotropic oopolymerization that is, polymerization proceeds without a change in the composition of either the feed or the copolymer. For azeotropic copolymerization the solution to Equation 8.5 with d[M[]/d[M2] = [Mi]/[M2] gives the critical composition. 

Example 8.3 Estimate the feed and copolymer compositions for the azeotropic copolymerization of acrylonitrile and styrene at 60°C. 

Azeotropic copolymerization of styrene and acrylonitrile in methanol Poly(vinylchloride)... 

The process is distinguished by the fact that the composition of the copolymer is close to that of the parent monomeric mixture (r = r2 = 1.0). In other words, in this case one can observe an azeotropic copolymerization. Thus, the substitution of an organometallic group by a hydrogen atom does not affect the double bond reactivity, which is probably due to the presence of a three-atom bridge. 

---