Polyfunctional condensation

Polyfunctional condensation has also been used to prepare ladder polymers from, for example, the following other intermediates ... 

The condensation of amino acids likewise may produce cyclic and/or linear products the same is true of virtually all polyfunctional condensation reactions. The conversion of cyclic monomers and dimers (or other cyclic low polymers) to chain polymers was discussed in the preceding chapter the reverse reaction may often occur as well. Thus the alternative ring and chain products which may be produced by condensation of a bifunctional monomer usually are interconvertible, but with varying degrees of facility. 

A pair of cross-linked chain units may be regarded as a single tetra-functional unit according to the scheme applied to polyfunctional condensation. In order to demonstrate the correspondence between the two treatments, consider the condensation of tetrafunctional units A... 

At the gel point, (3 —l) = l/p, which with the foregoing expression gives Eq. (14), thus establishing equivalence of the two procedures. The primary molecules in a condensation polymer must almost invariably conform to a most probable distribution (see Chap. VIII). The random cross-linking of primary molecules otherwise distributed in size has no counterpart in polyfunctional condensation, therefore. 

Although the theory is developed above for a polyfunctional condensation of the utmost simplicity, exploration of variants of this case indi-... 

The weight fraction of gel calculated for this case from Eq. (45) is plotted against a in Fig. 70. It will be observed that the formation of the infinite network is indicated to commence suddenly at the critical point. This prediction of the theory is abundantly confirmed by the characteristic abruptness with which gel appears in polyfunctional condensations. Also shown in Fig. 70 are the weight fractions Wx of various species as functions of a, calculated according to Eq. (36). 

Other polyfunctional condensations which proceed to gelation and beyond are subject to similar interpretation (see Appendix B). Differences occur only in quantitative details. 

The formation of multichain condensation polymers using an excess of A-B with a small amount of the multifunctional monomer R-A/, under conditions where no A can react with another A was described above in Sect. 1.2.1. Polyfunctional condensation polymerization using multifunctional monomers in other contexts can produce infinite... 

If the polyfunctional condensation of A-R-B/ i proceeds under the conditions of equal reactivity, the polydispersity increases as the reaction proceeds (as a increases), and approaches infinity as p — l. 9 The uncontrolled polycondensation of A-R-B/ i... 

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