Copolymerization, reactivity ratios

In studies of the polymerization kinetics of triaUyl citrate [6299-73-6] the cyclization constant was found to be intermediate between that of diaUyl succinate and DAP (86). Copolymerization reactivity ratios with vinyl monomers have been reported (87). At 60°C with benzoyl peroxide as initiator, triaUyl citrate retards polymerization of styrene, acrylonitrile, vinyl choloride, and vinyl acetate. Properties of polyfunctional aUyl esters are given in Table 7 some of these esters have sharp odors and cause skin irritation. 

Table 5. Free-Radical Copolymerization Reactivity Ratios,...

Young, L. J. Copolymerization Reactivity Ratios, in Polymer Handbook, (eds.) Brandrup, J.,... 

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 ... 

Typical Free Radical Chain Copolymerization Reactivity Ratios at 60°C... 

Greenley, R. Z., Free Radical Copolymerization Reactivity Ratios, pp. 153-266 in Chap. II in Polymer Elandbook, 3rd ed., J. Brandrup and E. H. Immergut, eds., Wiley-Interscience, New York, 1989a. 

The conclusion can be drawn that in template copolymerization reactivity ratios depend on the nature and concentration of the template used. Template controls composition and sequence distribution of monomer units in copolymers obtained. 

Vinyl acetate-butyl acrylate copolymers (0-100% butyl acrylate) were prepared by both batch and starved semi-continuous polymerization using sodium lauryl sulfate emulsifier, potassium persulfate initiator, and sodium bicarbonate buffer. This copolymer system was selected, not only because of its industrial importance, but also because of its copolymerization reactivity ratios, which predict a critical dependence of copolymer compositional distribution on the technique of polymerization. The butyl acrylate is so much more reactive than the vinyl acetate that batch polymerization of any monomer ratio would be expected to give a butyl acrylate-rich copolymer until the butyl acrylate is exhausted and polyvinyl acetate thereafter. 

Mechanistic Aspects of Cationic Copolymerizations The relative reactivities of monomers can be estimated from copolymerization reactivity ratios using the same reference active center. However, because the position of the equilibria between active and dormant species depends on solvent, temperature, activator, and structure of the active species, the reactivity ratios obtained from carbocationic copolymerizations are not very reproducible [280]. In general, it is much more difficult to randomly copolymerize a variety of monomers by an ionic mechanism than by a radical. This is because of the very strong substituent effects on the stability of carbanions and carbenium ions, and therefore on the reactivities of monomers substituents have little effect on the reactivities of relatively nonpolar propagating radicals and their corresponding monomers. The theoretical fundamentals of random carbocationic copolymerizations are discussed in detail and the available data are critically evaluated in Ref. 280. This review and additional references [281,282] indicate that only a few of the over 600 reactivity ratios reported are reliable. 

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. 

Otherwise, the method can be very misleading it failed badly when published data from certain copolymerizations were scrutinized by a specially developed analytical method for copolymerization data (52, 53). For these reasons, any published data on copolymerization reactivity ratios must be approached with caution, and the reader should be assured that the criteria just mentioned have been properly met. These precautions are especially true for siloxane copolymerizations, because reversibility can be established quickly, and rapid redistribution of comonomer units between rings and chains via equilibria 2 and 3 will confound any meaningful study of comonomer reactivity ratios. 

Table 4 Typical free-radical chain-copolymerization reactivity ratios...

Table 1.15. Selected values of free-radical copolymerization reactivity ratios, r-t and /2...

Karol and Garrick (2) have shown that the copolymerization reactivity ratios of ethylene and propylene change with the transition metal compound but not with the nature of the metal alkyl used. This indicates that the chain grows at the transition metal, which is sufficiently selective to control the reactivity ratio. 

TaUe 2. Copolymerization reactivity ratios (r, and r,) of activated (meth)acrylates (M,) and structural monomers (M,)... 

Copolymerization reactivity ratios are often considered to be more or less temperature invariant, but this is strictly true only over moderate temperature ranges. Considering the reactivity ratios in terms of their homopropagation and cross-propagation rate constants, one can express their temperature dependence using an Arrhenius-type equation ... 

Greenley R. Z. Free Radical Copolymerization Reactivity Ratios chapter II, In Brandrup J, Immergut E. H, Grulke E. A, editors. Polymer Flandbook. New York J. Wiley Sons Inc 1999. 

Tip 12 Copolymerization, reactivity ratios, and estimation of reactivity ratios. In a binary copolymerization of monomers and M2, reactivity ratios r and r2 are important parameters for calculating polymerization rate, copolymer composition, and comonomer sequence length indicators (see Chapter 6 for basic equations and further information). 

TABLE V Chain-Transfer Constants, Cj, and Copolymerization Reactivity Ratios of Diallyl Esters with Styrene (A/i) [7]... 

Kelen, T., Tiidos, R Analysis of the linear methods for determining copolymerization reactivity ratios. 1. New improved linear graphic method. 1. Macromol. Sci. Pure Appl. Chem. A9(l), 1-27 (1975)... 

Young, L.J., Copolymerization reactivity ratios, m Polymer Handbook, 2nd ed., Brandrup, J. and Immergut, H.H., Eds., John Wiley Sons, New York, 1975. 

Folic, A.L., Duever, T.A., and Penlidis, A., Case Studies and Literature review on the estimation of copolymerization reactivity ratios, /. Polym. Sci, Polym. Chem. Ed, 36, 812 (1988). 

The copolymerization reactivity ratios of 3 with other monomers correspond to a g = 0.82 and an c = 0.44 in the Alfrey-Price Q-e scheme, where Q describes the general monomer reactivity and e takes account of polar factors influencing copolymeri-... 

P. W. Tidwell and G. A. Mortimer, Science of determining copolymerization reactivity ratios, J. 

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