PEG
Poly(ethylene glycol)
R effect
Resonance effect
RAFT
Reversible addition-fragmentation chain transfer
SEM
Scanning electron microscopy
TEG
Tri(ethylene glycol)
TEM
Transmission electron microscopy
TFA
Trifluoroacetic acid
THF
Tetrahydrofuran
XPS
X-ray photoelectron spectroscopy
XRD
Powder X-ray diffraction
1 Introduction
Condensation polymerization is an important method of polymerization that yields
not only engineering plastics such as polyamides, polyesters, and polyimides but
also π-conjugated polymers, which have recently received considerable attention
with the development of the information technology industry. Generally, polycondensation proceeds in a step-growth polymerization manner, in which condensation
reactions between molecules of all degrees of polymerization occur. In the absence
of side reactions or cyclization, the average degree of polymerization can be
estimated according to the theory established by Carothers [1] and Flory [2], and
the molecular weight distribution (M w /M n ) approaches a value of 2. It has been
difficult to synthesize condensation polymers having controlled molecular weight
with a narrow molecular weight distribution via step-growth polymerization. To
synthesize a polymer with controlled molecular weight and low polydispersity, the
polymerization should start from an initiator unit and proceed via chain-growth
polymerization without disproportionation or termination. This is the case for
so-called living polymerization. Since the discovery of anion living polymerization
by Szwarc in 1956 [3], many kinds of living polymerizations have been developed
and used to synthesize well-defined polymers with controlled molecular weight and
a narrow molecular weight distribution. These polymerization methods have also
afforded polymer architectures, such as block and graft copolymers, as well as star
polymers, which could construct self-assembled supramolecular architectures with
defined shapes and properties. In general, however, living polymerization had been
applicable only to addition polymerization of vinyl monomers and exothermic
ring-opening polymerization of cyclic monomers, not to polycondensation and
polyaddition. If the mechanism of condensation polymerization could be converted
from step-growth to chain-growth, living condensation polymerization would be
possible.
In condensation polymerization of AB monomers, the chain-growth mechanism
could be involved in the following two cases: (1) A change in the effect of the
substituent (“change of the substituent effect”) induced by bond formation of
monomers with initiator and polymer chain end drives the reactivity of the polymer
Chain-Growth Condensation Polymerization for Controlled Synthesis of Polymers
193
Poly(ethylene glycol)
R effect
Resonance effect
RAFT
Reversible addition-fragmentation chain transfer
SEM
Scanning electron microscopy
TEG
Tri(ethylene glycol)
TEM
Transmission electron microscopy
TFA
Trifluoroacetic acid
THF
Tetrahydrofuran
XPS
X-ray photoelectron spectroscopy
XRD
Powder X-ray diffraction
1 Introduction
Condensation polymerization is an important method of polymerization that yields
not only engineering plastics such as polyamides, polyesters, and polyimides but
also π-conjugated polymers, which have recently received considerable attention
with the development of the information technology industry. Generally, polycondensation proceeds in a step-growth polymerization manner, in which condensation
reactions between molecules of all degrees of polymerization occur. In the absence
of side reactions or cyclization, the average degree of polymerization can be
estimated according to the theory established by Carothers [1] and Flory [2], and
the molecular weight distribution (M w /M n ) approaches a value of 2. It has been
difficult to synthesize condensation polymers having controlled molecular weight
with a narrow molecular weight distribution via step-growth polymerization. To
synthesize a polymer with controlled molecular weight and low polydispersity, the
polymerization should start from an initiator unit and proceed via chain-growth
polymerization without disproportionation or termination. This is the case for
so-called living polymerization. Since the discovery of anion living polymerization
by Szwarc in 1956 [3], many kinds of living polymerizations have been developed
and used to synthesize well-defined polymers with controlled molecular weight and
a narrow molecular weight distribution. These polymerization methods have also
afforded polymer architectures, such as block and graft copolymers, as well as star
polymers, which could construct self-assembled supramolecular architectures with
defined shapes and properties. In general, however, living polymerization had been
applicable only to addition polymerization of vinyl monomers and exothermic
ring-opening polymerization of cyclic monomers, not to polycondensation and
polyaddition. If the mechanism of condensation polymerization could be converted
from step-growth to chain-growth, living condensation polymerization would be
possible.
In condensation polymerization of AB monomers, the chain-growth mechanism
could be involved in the following two cases: (1) A change in the effect of the
substituent (“change of the substituent effect”) induced by bond formation of
monomers with initiator and polymer chain end drives the reactivity of the polymer
Chain-Growth Condensation Polymerization for Controlled Synthesis of Polymers
193