Copolymerization reactivity ratios, homogeneous

Barrett and Thomas (10)proposed that these effects of differential monomer adsorption could be modeled by correcting homogeneous solution copolymerization reactivity ratios with the monomer s partition coefficient between the particles and the diluent. The partition coefficient is measured by static equilibrium experiments. Barrett s suggested equations are ... 

However, this does not preclude mini emulsion copolymerization in a CSTR for extremely water-insoluble comonomers. In spite of the fact that the copolymer composition in the continuous miniemulsion is less than that predicted using the homogeneous copolymerization reactivity ratios, the miniemulsion copolymer might be more uniform than the macroemulsion copolymer, where the possibility of significant droplet nucleation could lead to two separate homopolymers or, at the very best, copolymers of various composition. Therefore, it is very important to use CSTR data to scale up a continuous miniemulsion copolymerization product to take into account the different particle growth kinetics for batch and continuous reactors. 

Vinyhdene chloride copolymerizes randomly with methyl acrylate and nearly so with other acrylates. Very severe composition drift occurs, however, in copolymerizations with vinyl chloride or methacrylates. Several methods have been developed to produce homogeneous copolymers regardless of the reactivity ratio (43). These methods are appHcable mainly to emulsion and suspension processes where adequate stirring can be maintained. Copolymerization rates of VDC with small amounts of a second monomer are normally lower than its rate of homopolymerization. The kinetics of the copolymerization of VDC and VC have been studied (45—48). 

Bajoras and Makuska investigated the effect of hydrogen bonding complexes on the reactivities of (meth)acrylic and isotonic acids in a binary mixture of dimethyl sulfoxide and water using IR spectroscopy (Bajoras and Makuska, 1986). They demonstrated that by altering the solvent composition it was possible to carry out copolymerization in the azeotropic which resulted in the production of homogeneous copolymers of definite compositions at high conversions. Furthermore, it was shown that water solvent fraction determines the rate of copolymerization and the reactivity ratios of the comonomers. This in turn determines the copolymer composition. 

In homogeneous copolymerization, the instantaneous composition of copolymer is decided only by monomer reactivity ratio. On the contrary, in emulsion copolymerization, the copolymer composition depends not only on the monomer reactivity ratio but also on the distribution of monomers between oil (polymer-monomer particles) and aqueous phases (18). 

Some polymer-composition vs. conversion curves were obtained for the copolymerizations with different f s (Figure 2), and all of them seem to intersect the ordinate at 1.0. From the initial slope of the curves and the monomer ratio in the aqueous phase the monomer reactivity ratio was calculated, but the calculation resulted in a negative r2. Therefore, it was concluded that the copolymerization could not be regarded as a homogeneous one even just after the beginning of the reaction. The first stage was considered to be a transitional stage to establish the particle formation. 

All the mentioned types of the nontrivial dynamic behavior are excluded for the systems where the reactivity ratios ry can be described by the expressions of the well-known Alfrey-Price Q-e scheme [20], and as a result they are to follow the simplified terminal model (see Sect. 4.6). In these systems, due to the relations Bj(X)/Bj(x) = ajj/ajj which holds for all i and j, the functions 7e,-(2) according to relations (4.10) are the ratios of the homogeneous polynomials of degree 2. Besides, for the calculations of the coefficients ak of Eq. (5.11) one can use the simple formulae presented in terms of determinants Dj and D [6, p. 265]. The theoretical analysis [202] leads to the conclusion that in such systems even the limited cycles are not possible and all azeotropes are certainly unstable. Hence any trajectory H(p) and X(p) when p -> 1 inevitably approaches the SP corresponding to the homopolymer the number of which can be from 1 to m. The set of systems obtained due to the classification within the framework of the simplified model essentially impoverishes in comparison with the general case of the terminal copolymerization model since some types of systems cannot be principally realized under the restrictions which the Q-e scheme puts on the reactivity ratios r. ... 

Schuller [150] and Guillot [98] both observed that the copolymer compositions obtained from emulsion polymerization reactions did not agree with the Mayo Lewis equation, where the reactivity ratios were obtained from homogeneous polymerization experiments. They concluded that this is due to the fact that the copolymerization equation can be used only for the exact monomer concentrations at the site of polymerization. Therefore, Schuller defined new reactivity ratios, TI and T2, to account for the fact that the monomer concentrations in a latex particle are dependent on the monomer partition coefficients (fCj and K2) and the monomer-to-water ratio (xp) ... 

All IR investigations of sequence distribution so far published rely on the terminal copolymerization model, which assumes that the kinetics of copolymerization are governed only by the probability that monomer units from the feed will be added to the last unit of the growing chain, and that there is only one active site present in the catalyst system, whether homogeneous or heterogeneous. As will be shown later (Section 3.4), this is only an approximation multiple active species are formed by many soluble Ziegler-Natta catalysts, so that the product of reactivity ratios determined from the normal copolymerization equation does not always exactly predict the actual sequence distribution in the copolymer. 

A measure of the relative reactivities of the monomers involved in copolymerization is reflected in their reactivity ratios and r2, the subscripts referring to monomers 1 and 213. Thus, when monomer 2 was sodium ethylenesulfonate, r2 was found to be close to zero while r (acrylamide) = 14.9 and r1 (sodium acrylate) = 5.8. A similar sluggishness in copolymerization with less-polar monomers was also found for other sulfonates. Izumi and coworkers studied the copolymerization of sodium allylsulfonate (MJ with acrylonitrile (M2) in dimethyl sulfoxide (DMSO) and DMSO-water mixtures. They found considerably lower values for r2 as compared to in aqueous DMSO and attributed it to lack of homogeneity , although no phase separation was observed in this medium14. 

A detailed structure characterization of isobutylene and 0-pinene copolymers has been carried out including homogeneity studies (by GPC), quantitative composition and sequence analysis (by PMR and reactivity ratios) and molecular weight determinations (by osmometry and viscometry). Analysis of our data leads us to conclude that isobutylene and 0-pinene can be readily copolymerized to reasonably high molecular weight materials and that the products are perfectly random, statistical copolymers showing no detectable tendency for blockiness . 

Monomer reactivity ratios have been determined for copolymerization of acrylonitrile with most of the common monomers. These constants make it possible to predict the composition of copolymer fonning from any given monomer mixture. When these ratios are unavailable, one may apply the Alfrey-Frice theory and accept Q and e values of about 0.6 and - -1.2, respectively. Usually, the conuposition of the product diSera from that of the starting mixture, and in order to obtain a homogeneous product, it is necessary to reduce the rate of addition of the more active monomer. Several hundred monomerB have been proposed for use with acrylonitrile, but only a few of these copolymers are used commercialiy. 

Styrene and DVB isomers by means of nonlinear least-squares analysis (such an approach to the treatment of experimental data was demonstrated to give a smaller error [17]). The new values of r and are also given in Tables 1.1 and 1.2. The numerical values of the copolymerization constants changed, but the general conclusion remained the same the distribution of crosslinks is extremely inhomogeneous in styrene—p-DVB copolymers. It is more homogeneous in styrene—m-DVB networks, although m-DVB is stiU predominantly incorporated into the network. With a probability of 95%, the compositions of styrene—p-DVB and styrene—m-DVB copolymers were found to be described by monomer reactivity ratios of = 0.30 and f2 = 1.02 and fj = 0.62 and f2 = 0.54, respectively. 

A large number of studies have been made of the reactivity ratios in this copolymerization, both in homogeneous and emulsion systems, and the average... 

Table 1 shows the Q and e values and the monomer reactivity ratios rj and T2 for the radical copolymerization process. Since the monomer reactivity ratios between negatively birefringent methyl methacrylate (MMA) and positively birefringent 2,2,2-trifluoroethyl methacrylate (3FMA) and benzyl methacrylate (BzMA) are nearly equal to unity, these monomers can be randomly copolymerized, resulting in homogeneous and transparent copolymers. 

Most monomers have different reactivity ratios, which lead to production of copolymers that do not have the same composition of the monomer mixture. In batch copolymerization, the copolymer produced at the beginning of the process is richer in the most reactive monomer, while the copolymer becomes richer in the less reactive monomer at the end of the batch. This composition drift causes the production of heterogeneous polymer mixtures, which may be deleterious for the performance of the polymer material. With the exception of the azeotropic reactions, most copolymerization systems experience composition drifts during batch copolymerizations, which must be corrected if homogeneous copolymer materials are to be produced. For this reason, copolymerizations are usually performed in semibatch (with manipulation of monomer feed flow rates) or continuous mode. 

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