INDEX side-chain reactivity

Although a wide variety of heterocycle/side-chain combinations can be used in the Boulton-Katritzky rearrangement, among these, the most commonly used heterocycle has been the 1,2,4-oxadiazole. This is due to the relative ease with which it is synthesized as well as the fact that it has a very low index of aromaticity. Its heightened chemical reactivity has made it an important target for medicinal and materials chemists and the subject of multiple reviews in the last several years. ... 

The first term on the right-hand side of Eq. (3.23) describes the input and output from the kth reactor, the second describes the increase in chain length due to propagation, the next two are responsible for the variation in the number of branching b and active centers i due to chain transfer, and two last terms describe the formation of short (1=1) linear (fo = 1) chains due to instantaneous initiation and chain transfer to solvent. In the general case, the temperature in different reactors can be varied therefore, the reactivities also bear index k. 

This chapter has discussed the analysis of reactors for step-growth polymerization assuming the equal reactivity hypothesis to be valid. Polymerization involves an infinite set of elementary reactions under the assumption of this hypothesis, the polymerization can be equivalently represented by the reaction of functional groups. The analysis of a batch (or tubular) reactor shows that the polymer formed in the reactor cannot have a polydispersity index (PDI) greater than 2. However, the PDI can be increased beyond this value if the polymer is recycled or if an HCSTR is used for polymerization. A comparison of the kinetic model with experimental data shows that the deviation between the two exists because of (1) several side reactions that must be accounted for, (2) chain-length-dependent reactivity, (3) unequal reactivity of various functional groups, or (4) comphca-tions caused by mass transfer effects. 

---