Homopolymerization kinetic expression

The mechanism for the homopolymerization of epoxides may proceed via a bimolecular reaction yielding a symmetrical 2,5-disubstituted dioxane as shown in Reaction Scheme 6. This reaction should be described by the following kinetic expression for the disappearance of epoxides ... 

The kinetic expressions of Section 4.4.2 are substituted into overall material and energy balances to construct a model to represent an FRP process. For a well-mixed reactor system, Eqs. (84)-(89) comprise the general system of equations for homopolymerization. 

The rate expression for the radical-initiated homopolymerization kinetic studies of (Ti -vinylcyclopentadienyl)methyltricarbonyltungsten (20) in benzene is as follows (see also Scheme... 

In evaluating the kinetics of copolymerization according to the chemical control model, it is assumed that the termination rate constants k,AA and A,Br are known from studies on homopolymerization. The only unknown in the above expression is the rate constant for cross termination (AtAB)- The rate constant for this reaction in relation to klAA and kmB is given by the parameter . 

According to the kinetic scheme presented for cationic homopolymerizations, the apparent propagation rate constant (kptj) is expressed as... 

Techniques. Experimentally, several techniques are important tools for the study of photoimaging parameters. Though solution techniques common to photomechanistic studies can be applied in some instances, they must be used with care in photopolymer systems. The kinetic and rate expressions just described are only valid in model systems in which homopolymerization processes are the only ones which occur. Kinetic complications can result if crosslinking processes are important. Network formation is common, and represents a further complication. In practice, conversion must be kept to a low level in order to prevent depletion of initiator or monomer below acceptable levels. 

However, for several epoxy-amine systems, the simple kinetic model expressed by the set of Eqs (5.18) (5.21) does not provide a good fitting with experimental results. Reaction mechanisms, including the formation of different kinds of complexes, have been postulated to improve the kinetic description (Flammersheim, 1998). Also, a more general treatment of the kinetics of epoxy-amine reactions would have to include the possibility of the homopolymerization of epoxy groups in the reaction path. Sets of kinetic equations including this reaction have been reported (Riccardi and Williams, 1986 Chiao, 1990 Cole, 1991). 

Theoretical treatment of this polymerization is difficult because of the presence of both primary and secondary amine reactions as well as tertiary amine catalyzed epoxy homopolymerization. To obtain kinetic and viscosity correlations, empirical methods were utilized. Various techniques that fully or partially characterize such a system by experimental means are described in the literature ( - ). These methods Include measuring cure by differential scanning calorimetry, infra-red spectrometry, vlsco-metry, and by monitoring electrical properties. The presence of multiple reaction mechanisms with different activation energies and reaction orders (10) makes accurate characterizations difficult, but such complexities should be quantified. A dual Arrhenius expression was adopted here for that purpose. 

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