Chain transfer constants Mayo equation

The Mayo equation (Equation 6.42) that gives positive slopes when the data is plotted (such as Figure 6.3) is the reciprocal relationship derived from the expression cited earlier. The ratio of the rate of cessation or termination by transfer to the rate of propagation is called the chain transfer constant (Cs). 

From these results, the chain transfer constants to the solvent were determined by the Mayo s equation (22). 

Equation (6.148), often referred to as the Mayo equation, shows the quantitative effect of various transfer reactions on the number average degree of polymerization. Note that the chain transfer constants, being ratios of the respective rate constants for chain transfer (Rtr) to the rate constant for propagation (kp), are dimensionless quantities dependent on the types of both the monomer and the material causing chain transfer as well as on the temperature of reaction. 

Various methods can be employed, based on the Mayo equation, to determine the values of the chain transfer constants. The following sections review some of these methods. 

Mayo defined a chain transfer constant that could be empirically determined by Equation 1.22. P is the degree of polymerization, S and M are concentrations of solvent and monomer respectively, and Pq is the degree of polymerization in the absence of solvent. Thiols are particularly effective (albeit stoichiometricaUy as in 1.20 and 1.21) reagents for chain transfer [66]. 

The efficienqf of a chain transfer catalyst has traditionally been measured by its chain transfer constant (Cs), which is the ratio of the rate constant for chain transfer (feu) to that for propagation (fep). Values of Cs are generally determined from the slope of a plot of 1/DP vs. (CTA)/(M] (the Mayo method. Equation 1.27 [74]), in which DP is the degree of polymerization, CTA is the chain transfer agent, and M is monomer. 

The activity of the transfer agent is usually de ned in terms of their chain transfer constants (Ctr = ktrlkp). Traditionally, chain transfer constants have been evaluated by applying the Mayo equation [cf. Eq. (6.122)] ... 

The concentrations of both chain transfer agent and initiator are important for the polymerization when the concentration of HPMA is constant. The molecular weight of the ST HPMA polymers was regulated by the concentration ratio of mercaptan (S) to HPMA (M), according to the Mayo equation, lT>P (end) = + Q[S]/[M] [27]. DP (end) are the num-... 

The use of organometallic compounds as chain-transfer catalysts in free-radical polymerization has been widely studied. One objective is the production of polymers with terminal vinyl groups and lower molecular weight components compared with polymerization in the absence of chain-transfer catalysts. Gomplexes of cobalt(ii) have been used as effective catalysts, but the instability of the intermediate cobalt hydride does not permit firm establishment of the reaction mechanism. To address this issue, several chromium compounds have been applied as catalysts for the polymerization of methylmethacrylate (MMA) and styrene. The temperature dependence of the rate constant for free-radical polymerization of MMA for catalyzed chain transfer by (GsPh5)Gr(GO)3 has been determined using the Mayo equation. ... 

Styrene-SQ., Copolymers. I would now like to discuss two systems which illustrate the power of C-13 nmr in structural studies. The first is the styrene-SO system. As already indicated, this is of the type in which the chain composition varies with monomer feed ratio and also with temperature at a constant feed ratio (and probably with pressure as well.) The deviation of the system from simple, first-order Markov statistics, —i.e. the Lewis-Mayo copolymerization equation—, was first noted by Barb in 1952 ( ) who proposed that the mechanism involved conplex formation between the monomers. This proposal was reiterated about a decade later by Matsuda and his coworkers. Such charge transfer com-... 

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