Vol. 24, No. 6
from Pure and Applied Chemistry
Relating to Stereochemically Asymmetric Polymerizations (IUPAC Recommendations
Hatada, J. Kahovec, M. Barón, K. Horie, T. Kitayama, P. Kubisa,
G. P. Moss, R. F. T. Stepto, and E. S. Wilks
Pure and Applied
74, No. 6, pp. 915-922 (2002)
polymerization has been of interest to many academic and industrial
polymer scientists, but IUPAC has made no explicit reference to the
classification and definitions of reactions involving the asymmetric
synthesis of polymers. This document presents definitions concerned
with asymmetric and related polymerizations, with examples included
to clarify the meaning of the definitions.
polymerization is defined as "A polymerization that proceeds
in an unsymmetrical manner in terms of chirality under the influence
of chiral features present in one or more components of the reaction
system." The asymmetric polymerizations embrace two main categories,
"asymmetric chirogenic polymerizations" and "asymmetric enantiomer-differentiating
polymerizations," which are defined as follows:
chirogenic polymerization: An asymmetric polymerization in which
the polymer molecules formed contain one (or more) new type(s) of elements
of chirality not existing in the starting monomer(s).
example of asymmetric chirogenic polymerization: Polymerization
of penta-1,3-diene by 1,4-addition with an optically active catalyst
gives an optically active polymer comprising configurational repeating
units with predominantly one type of chirality center.
enantiomer-differentiating polymerization: An asymmetric polymerization
in which, starting from a mixture of enantiomeric monomer molecules,
only one enantiomer is polymerized.
example of asymmetric enantiomer-differentiating polymerization:
Polymerization of racemic 3-methylpent-1-ene (MP) using an optically
active catalyst may give an optically active polymer by a polymerization
that is partially asymmetric; preferential consumption of one of
the two enantiomers leaves a monomer mixture having optical activity.
chirogenic polymerizations give helical polymer molecules of only one
screw sense that usually show optical activity due to the helicity.
These polymerizations are termed "asymmetric helix-chirogenic polymerizations."