Chain copolymerization azeotropic

Under homophase synthesis in real systems the azeotrop (a) exists only provided n < 1 and r2 < 1. In this case, however, it is a repeller, unlike in the case of interphase copolymerization where the azeotrop (b) is an attractor. This means that at the final stage of homophase copolymerization homopolymer molecules are primarily formed in all real systems whereas under the interphase synthesis the majority of copolymer chains formed at p —> 1 have the azeotropic composition x. ... 

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. 

The general formulae (5.1), (5.3), and (5.7) are still valid under the transition to the more complicated models described in Sect. 2. In the case of the penultimate model it concerns also the dynamic Eqs. (5.2) into which now one should substitute the dependence j (i) obtained after the solution of the problem of the calculation of the stationary vector tE(x) of the Markov chain corresponding to this model. Substituting the function X1(x1) obtained via the above procedure (see Sect. 3.1) into Eq. (5.2) for the binary copolymerization we can find its explicit solution expressed through the elementary functions. However, this solution is rather cumbersome and has no practical importance. It is not needed even for the classification of the dynamic behavior of the systems, which can be carried out only via analysis of Eq. (5.5) by determining the number n = 0,1,2, 3 of the inner azeotropes in the 2-simplex [14], The complete set of phase portraits of the binary... 

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... 

It should be noted, too, that the r values for this system do not permit an azeotropic polymerization, as predicted by Eq. (2.39). With respect to the distribution of styrene monomer units in the copolymer, the monomer reactivity ratio product, rers = 0.8, is close to a value of 1.0, which would correspond to an ideal copolymerization (Odian, 2004b) which would correspond to a random distribution of styrene units along the chain. For an ideal copolymerization, the relative rates of incorporation of the two monomers are independent of the chain end unit as predicted by Eq. (2.42). 

The quantities k , k,p, kpp, and kp, are the rate constants of the four basic propagation reactions of copolymerization. The Stockmayer distribution function takes into account only a chemical polydispersity resulting fi om the statistical nature of copolymerization reactions. This means that all units of all chains are formed under identical conditions. If a monomer is removed from the reacting mixture at a rate which changes the monomer concentration ratio, the monomer concentration will drift, forming a copolymer which varies in the average composition and is broader in the chemical distribution. No such chemical polydispersity can be described by the Stockmayer distribution. Therefore, Eq. (84) has to be restricted in its application to random copolymers synthesized at very low conversions or under azeotropic conditions. For azeotropic copolymers, the feed monomer concentrations [a ] and are chosen in such a way that the second factor on the right-hand side of the basic relation of copolymerization kinetics... 

Azeotropic t-buOH/water was used as the solvent for VA/AA copolymerization at an operating temperature of 65°C, because of the relatively low chain transfer constants to both VA and AA. Also, reactor runs verify that the reactor fluid turned a little cloudy from the early stages of reaction to almost the end of the run. 

As the product Ta b decreases there is an increasing tendency towards alternation in the additions of monomer molecules to the propagating chains. The extreme case of azeotropic copolymerization is Ta = a b = 0 and always produces perfectly alternating copolymers, irrespective of the value of /a (i.e. Fa = 0 50 for 0homopropagation reactions do not occur. 

Several boundary combinations of reactivity ratios are illustrated in Figure 4. For the case in which neither active center shows any preference for any monomer species, i.e., ri = f2 = 1, copolymer composition is determined at all times solely by the concentration of the respective monomer species in the feed composition. This defines an azeotropic composition over the entire range of monomer feed compositions. For the other extreme case, the one in which each active center adds exclusively the monomer other than that which represents the terminus on the active chain, i.e., ri = T2 = 0, an alternating copolymer is formed in which half of the polymer chain consists of homopolymer of Mi and the second half of homopolymer of M2. In the case in which either active center shows preference for one, the more reactive, monomer, i.e., ri > 1 and T2 < 1, the copolymer is always richer in that monomer and the feed composition is conversely richer in the less reactive monomer. In the final case (Fig. 4), in which each active center prefers cross-propagation to homo-propagation, i.e., ri < 1 and T2 < 1, a tendency exists toward alternation. Copolymerizations with preferred alternation... 

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