Chain polymerization kinetics, general

Bamford43,59 63 has proposed a general treatment for solving polymerization kinetics with chain length dependent kt and considered in some detail the ramifications with respect to molecular weight distributions and the kinetics of chain transfer, retardation, etc. 

It is widely acknowledged that polymerization can proceed according two general mechanisms of reaction step polymerization and chain polymerization. These two mechanisms are quite different and consequently their kinetics, molecular weight distribution, influence of reaction parameters on the process, etc., are very different in both cases. For the same reasons, the template reactions differ, depending on their mechanisms of the polymerization processes. 

It can be shown that the degree of polymerization in emulsion polymerization can be derived from general polymerization kinetics [Eq. (3.79)] by neglecting chain transfer ... 

Now let s consider the kinetics of other types of chain polymerizations. Except that now you re going to do the work But it s not that bad, you just follow the general scheme that we set up for free radical polymeriza-... 

There are two general methods of synthesizing IPN s, see Figure 1. For sequential IPN s, polymer network I is synthesized, and monomer II plus crosslinker and activator is swelled in and polymerized. For simultaneous interpenetrating polymer networks, SIN s, both monomers and their respective crosslinkers and activators are mixed together and polymerized, usually by separate and non-interfering kinetic methods such as stepwise and chain polymerizations. Of course, there are many... 

The kinetics of polycondensation and polyaddition reactions follow the same general scheme, but both differ sharply from the kinetics of addition or chain polymerization. 

Table 6.2 shows the general range of values of the various concentrations, rates, and rate constants pertaining to the above kinetic scheme. These values are typical of radical chain polymerizations. 

The aforesaid complexities make it virtually impossible to write explicit general equations for the rate of polymerization, kinetic chain length, average degree of polymerization as has been done above for a completely dissociated ionic initiator. With the exception of those simple cases discussed above, each system in anionic polymerization represents a kinetically unique problem and must be solved separately. 

CHAIN POLYMERIZATION BY FREE RADICAL MECHANISM 2.4.1 General Kinetics... 

Copolymerization involves the simultaneous chain polymerization of a mixture of two or more monomers (Hillmyer, 2012 Ham and Alfrey, 1964 Odian, 2004a Tirrell, 1986). Aside from the general kinetic considerations which govern these chain reactions, as described earlier, there is imposed an additional... 

It is important to emphasize that this kinetic treatment is valid for any chain polymerization mechanisms, i.e., free radical, cationic, anionic, and coordination. However, in the case of the ionic mechanisms, the type of initiator used and the nature of the solvent medium may influence the ri and r2 values. This is due to the fact that the growing chain end in ionic systems is generally associated with a counterion, so that the structure and reactivity of such chain ends can be expected to be affected by initiator and the solvent. This will be discussed in Section 2.8.3. 

Copolymer composition can be predicted for copolymerizations with two or more components, such as those employing acrylonitrile plus a neutral monomer and an ionic dye receptor. These equations are derived by assuming that the component reactions involve only the terminal monomer unit of the chain radical. This leads to a collection of N x N component reactions and x 1) binary reactivity ratios, where N is the number of components used. The equation for copolymer composition for a specific monomer composition was derived by Mayo and Lewis [74], using the set of binary reactions, rate constants, and reactivity ratios described in Equation 12.13 through Equation 12.18. The drift in monomer composition, for bicomponent systems was described by Skeist [75] and Meyer and coworkers [76,77]. The theory of multicomponent polymerization kinetics has been treated by Ham [78] and Valvassori and Sartori [79]. Comprehensive reviews of copolymerization kinetics have been published by Alfrey et al. [80] and Ham [81,82], while the more specific subject of acrylonitrile copolymerization has been reviewed by Peebles [83]. The general subject of the reactivity of polymer radicals has been treated in depth by Jenkins and Ledwith [84]. 

It is important to monitor photopolymerization reactions as they provide valuable information about the reaction kinetics, which can help optimize photocurable formulations to achieve desired properties, such as structural, physical, and mechanical, in the cured materials. This section provides a detailed summary of the available characterization techniques commonly used to investigate photopolymerization reactions. The parameters that are generally investigated are the rate of polymerization Rp), DC and the amount of RCs, induction period (ti), quantum yield of polymerization, kinetic chain lengths, and gelation time. 

The kinetic picture of cationic chain polymerization varies considerably. Much depends upon the mode of termination in any oarticular system. A general scheme for initiation, propagation, and termination is presented below. ° By representing the coinitiator as A, the initiator as RH, and the monomer as M, we can write ... 

Copolymerization involves the simultaneous chain polymerization of a mixture of two or more monomers [89-92], Aside from the general kinetic considerations which govern these chain reactions, as described earlier, there is imposed an additional feature, i.e., the relative participation of the different monomers during the growth of the chain. This new parameter is most important, since it controls the composition of the copolymer. Systems involving more than two monomers are difficult to resolve in this respect, but it has been found possible to treat the case of a pair of monomers with relative ease [91,93-95]. 

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