Limits of the chemical composition heterogeneity of random copolymers

Abstract

One of the characteristic features of copolymers is their chemical heterogeneity. Examples are given of the dependence of conversion heterogeneity in the chemical composition of random copolymers on the initial composition of the monomer mixture, along with typical examples of the differential distribution functions of chemical composition. The maximum attainable values of the conversion heterogeneity parameter have been calculated depending on the copolymerization parameters. The conditions are discussed under which copolymers may acquire chemical heterogeneities high enough to be perceived or determined by fractionation or light scattering. Limits are estimated beyond which the chemical heterogeneity becomes undetectably low and the copolymers can be regarded as chemically homogeneous.

Dynamics of Composition Fluctuations in Statistical Copolymer Solutions

“… 42. This value is smaller than the corresponding values of κ o (Table2) for the sample sm2/8 (20 vol % of styrene).…”

“…31,40,41 The maximum attainable value of the composition polydispersity for styrene-methyl methacrylate system was found 2 × 10 -3 for initial composition 21.5 vol % of styrene at conversion 0.9. 42 The composition polydispersity decreases to zero on approaching the PMMA homopolymer or copolymer with the azeotropic composition which for this particular system is in the vicinity of 50 vol % of styrene. 31 Thus, the variations of the ratio A s (n c 2 n s 2 ) 2 /A f N (Table 2) with the copolymer composition qualitatively agree with the above predictions and also support the above interpretation of the slow mode.…”

“…An independent estimate of the composition polydispersity is a serious experimental problem . Nevertheless, it is possible to calculate the variance in the copolymer chemical composition for random copolymers using the monomer reactivity ratios. ,, The maximum attainable value of the composition polydispersity for styrene-methyl methacrylate system was found 2 × 10 -3 for initial composition 21.5 vol % of styrene at conversion 0.9 …”

Distribution of the Chemical Composition of Block and Graft Copolymers Assuming Gamma Distribution of Molecular Weights of the Precursor Blocks

“…scattering, 16 or the chemical heterogeneity of copolymers can be characterized by another method. 15 Figure 7 shows how the form of the distribution function of chemical composition is affected by the model chosen, i.e., by the mechanism of formation of the copolymer. As expected, the differences are relatively small if the molecular weight distributions of the precursors are very narrow and become increasingly pronounced with broadening polydispersity of the latter.…”

Modern aspects of quantitative theory of free-radical copolymerization

“…In particular the discussion of the different theoretical aspects of the binary copolymerization is reported in a number of reviews by Soviet authors [186][187][188][189]. By means of numerical calculations there were analyzed [190][191][192] the limits of the validity of the traditional assumption which allows to ignore the "instantaneous" component of composition distribution of the copolymers produced at high conversions. The calculations of the statistical characteristics of such polymers within the framework of the kinetic models different from the terminal one do not present any difficulties at all.…”