05-01-2013, 03:54 PM
chain polymerization
A chain reaction in which the growth of a polymer chain proceeds exclusively
by reaction(s) between monomer(s) and reactive site(s) on the polymer
chain with regeneration of the reactive site(s) at the end of each growth
step.
Notes:
1. A chain polymerization consists of initiation and propagation reactions,
and may also include termination and chain transfer reactions.
2. The adjective ‘chain’ in ‘chain polymerization’ denotes a ‘chain reaction’
rather than a ‘polymer chain’.
3. Propagation in chain polymerization usually occurs without the formation
of small molecules. However, cases exist where a low-molar-mass
by-product is formed, as in the polymerization of oxazolidine-2,5-diones
derived from amino acids (commonly termed amino-acid N-carboxy anhydrides).
When a low-molar-mass by-product is formed, the adjective
‘condensative’ is recommended to give the term condensative chain polymerization.
4. The growth steps are expressed by:
Px + M ® Px +1 (+L) {x} Î {1, 2, ... ¥}
where Px denotes the growing chain of degree of polymerization x, M a
monomer and L a low-molar-mass by-product formed in the case of condensative
chain polymerization.
5. The term ‘chain polymerization’ may be qualified further, if necessary,
to specify the type of chemical reactions involved in the growth step, e.g.
ring-opening chain polymerization, cationic chain polymerization.
6. There exist, exceptionally, some polymerizations that proceed via chain
reactions that, according to the definition, are not chain polymerizations.
For example, the polymerization:
HS–X–SH + H2C=CH–Y–CH=CH2 ®
S–X–S–CH2–CH2–Y–CH2–CH2
proceeds via a radical chain reaction with intermolecular transfer of the
radical centre. The growth step, however, involves reactions between molecules
of all degrees of polymerization and, hence, the polymerization is
classified as a polyaddition. If required, the classification can be made more
precise and the polymerization described as a chain-reaction polyaddition.
1996, 68, 2306
A chain reaction in which the growth of a polymer chain proceeds exclusively
by reaction(s) between monomer(s) and reactive site(s) on the polymer
chain with regeneration of the reactive site(s) at the end of each growth
step.
Notes:
1. A chain polymerization consists of initiation and propagation reactions,
and may also include termination and chain transfer reactions.
2. The adjective ‘chain’ in ‘chain polymerization’ denotes a ‘chain reaction’
rather than a ‘polymer chain’.
3. Propagation in chain polymerization usually occurs without the formation
of small molecules. However, cases exist where a low-molar-mass
by-product is formed, as in the polymerization of oxazolidine-2,5-diones
derived from amino acids (commonly termed amino-acid N-carboxy anhydrides).
When a low-molar-mass by-product is formed, the adjective
‘condensative’ is recommended to give the term condensative chain polymerization.
4. The growth steps are expressed by:
Px + M ® Px +1 (+L) {x} Î {1, 2, ... ¥}
where Px denotes the growing chain of degree of polymerization x, M a
monomer and L a low-molar-mass by-product formed in the case of condensative
chain polymerization.
5. The term ‘chain polymerization’ may be qualified further, if necessary,
to specify the type of chemical reactions involved in the growth step, e.g.
ring-opening chain polymerization, cationic chain polymerization.
6. There exist, exceptionally, some polymerizations that proceed via chain
reactions that, according to the definition, are not chain polymerizations.
For example, the polymerization:
HS–X–SH + H2C=CH–Y–CH=CH2 ®
S–X–S–CH2–CH2–Y–CH2–CH2
proceeds via a radical chain reaction with intermolecular transfer of the
radical centre. The growth step, however, involves reactions between molecules
of all degrees of polymerization and, hence, the polymerization is
classified as a polyaddition. If required, the classification can be made more
precise and the polymerization described as a chain-reaction polyaddition.
1996, 68, 2306