Copolymer approximate kinetic form

Using MAS C NMR, the resonances at 127 and 136 ppm were attributed to the cis and trans double bonds and that at 178 ppm was for the carbonyl groups. The composition of the copolymers was determined by elemental analysis, radioassay of C content in the labeled copolymers and NMR. The copolymers were found to have a composition of 95, 90, and 87 mol% acetylene. The molecular weight of the insoluble copolymers was determined by radioassay of the T content after adjustment for the kinetic isotope effect (KEF). At a reaction temperature of —78 C, copolymers in the form of thin film were obtained with A/n = approximately 4000, whereas at a reaction temperature of 25 C, only powder-like products with A/n = approximately 1000 were obtained. The homopolyacetylene was found to have A/ = 11 000 using... 

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. 

Since the composition of a copolymer chain is critical for determining its properties, understanding how the kinetics of the copolymerization impact the composition is an important consideration. To cut to the chase, the composition of a copolymer formed under a particular set of conditions depends on the relative rates of the four principal reactions. This in turn depends on the rate constants (e.g., those shown in Figure 12) and concentrations of reactive species and monomers. Using either a steady-state approximation or a polymerization statistics derivation, one can determine the following expression for the relative amount of monomer A in copolymer given the amount in the feed through equation [12] where Fa is the mole fraction of A in the copolymer and/a is the mole fraction of A in the feed ... 

The fact that copolymer and homopolymer runaway envelops agreed both qualitatively and quantitatively suggests that perhaps complex copolymerization kinetics might be successfully approximated by simpler kinetics, similar to the homopolymer form. It Is proposed that be replacing parameters in the homopolymer balances by their copolymer analogs, i.e., Xm, Xq and e = Xa Ac by A, ... 

Controlled radical polymerization allows the synthesis of block copolymers from addition monomers without the kinetic constraint of the reactivity ratios. Thus, for CRP, it is perhaps the CSD rather than the CCD that is important in characterizing the polymer. Zargar and Schork [6, 8] and Ye and Schork [9,10] have modeled the various chemistries for CRP. Their models include the CSD. Information about the CCD comes naturally from their analysis of the CSD. Mathematical modeling of CRP copolymerization would take (to a first approximation) the same form as the living (ionic) polymerization analysis given earlier. 

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