Introduction - Polycondensation: History and New Results - page 1

Chapter 1
Introduction

For three reasons polycondensation is a polymerization process, which plays a
unique role in the history of chemistry in general, and in the history of polymer
science in particular. Polycondensation was the first polymer forming reaction
sequence which existed on the early earth before living organisms appeared. It is
clear from the experiments of Stuart Miller [ 1 , 2 ] and other authors that whenever
organic molecules were formed on earth, a-and ß-amino acids were formed
together with a-hydroxy acids, such as glycolic and lactic acid. Heating and drying
of their aqueous solutions might have yielded their oligomers and polymers. The
second reason for the unique role of polycondensation is the fact that the first
polymer synthesized in a laboratory (although not intentionally) was poly(D,L-
lactic acid) which was obtained by heating of lactic acid in vacuo (see Sect. 2.1 in
Chap. 2 ) . The third reason is the fact that the first commercialized synthetic
polymers, namely Novolac and Bakelite, were polycondensates (see Chap. 2 ) .
The main purpose of this introduction is to present and discuss the definition of
the term ''polycondensation'', because in recent years an increasing number of
authors published misleading or definitely incorrect applications of his term. The
experimental and theoretical basis of step-growth polymerizations, in general, and
polycondensation, in particular, was elaborated by W. H. Carothers (see Chap. 3 )
and by P. J. Flory (see Chap. 4 ). Their results and conclusions are still valid
nowadays (for partial revisions see Chaps. 4 , 5 and 7 ) and form in all textbooks the
framework for chapters dealing with step-growth polymerizations. Polyconden-
sation and polyaddition are the two branches of step-growth polymerization, which
were defined by Flory via a kinetic scheme [ 3 ], which complements the kinetic
definition of chain-growth polymerization (see Chap. 16 ). In connection with step-
growth polymerizations the term polyaddition should be used instead of addition
polymerization, because the latter term is frequently applied to chain-growth
polymerizations of vinyl monomers and a-olefins. Polycondensation and polyad-
dition differ formally by the fact that each growing step of a polycondensation
involves elimination of an (usually) small molecule, such as H 2 O, HCl, MeOH etc.
This difference does not affect the kinetic course of both polymerization processes,
but it marks an enormous difference for the thermodynamic properties. A normal
polycondensation of non-cyclic monomers is characterized by a reaction entropy