TABLE OF CONTENTS Although, as indicated earlier, polyaddition and polycondensation did not figure prominently in the early explorations of rubber synthesis, it was one of the earliest general methods used for polymerization, because of its relative simplicity. It is thus not surprising that the earliest truly synthetic resins and plastics were of the polycondensate type, such as phenol formaldehyde and polyester. The concept of linking together reactive end groups to build large molecules is fairly simple to comprehend and also lends itself to a relatively simple mathematical analysis.
As stated previously, the kinetics of polyadditions and polycondensations follow the same rules as the simple monofunctional reactions [18, 20, 22, 25], as the reactivity of the functional groups is maintained [11, p. 75] regardless of chain length. The only new feature is, of course, the growth in molecular size, and this has been amenable to a mathematical analysis [11, p. 91]. Considering the type of reactions defined in Eqs. (2) and (3), in the normal case, where the number of A and B groups are equal, the chain lengths are easily predictable as a function of the extent of reaction. Thus, if p represents the fraction of end groups consumed at any given time, then the number-average number of units per chain ( X n) is given by 1/(1 ? p). Thus,
where M n is the number-average molecular weight of the polymer and M o is the molecular weight of a chain repeating unit. The...
