Chemistry Reference
In-Depth Information
lymers. The thermal and mechanical properties and also the stability of
industrial block-copolymers vary in broad limits.
The range of operating temperatures and the thermal stability of TPEs
have lately been extended owing to the use of solid blocks of high
T
Tglass.
(of
polysulfones or polycarbonates for instance) combined with soft blocks of
low
T
Tglass.
. Moreover, the incompatibility of those blocks results in indepen-
dence of elasticity modulus on temperature in broad temperature range.
Applying appropriate selection of chemical nature of blocks one can also
improve the other properties.
Some limitations and unresolved issues still exist in areas of synthe-
sis, analysis and characterization of properties and usage of block-copoly-
mers. This is a good stimulus for the intense researches and development
of corresponding fields of industry.
The most preferred methods of synthesis of block-copolymers are
the three following. The polymerization according to the mechanism of
“live” chains with the consecutive addition of monomers has been used
in the first one. The second is based on the interaction of two preliminary
obtained oligomers with the end functional groups. The third one is the
polycondensation of the second block at expense of end group of primar-
ily obtained block of the first monomer. The second and the third methods
allow one to use great variety of chemical structures.
So, to produce block-copolymers one can avail numerous reactions
allowing one to bind, within the macromolecule, blocks synthesized by
means of polycondensation at expense of joining or cycloreversion.
The second method of synthesis of block-copolymers allows one to
produce polymers after various combinations of initial compounds, one
among which is that monomers able to enter the reaction of condensation
are added to oligomers obtained by polycondensation.
Generally, the bifunctional components are used for creating the block-
copolymers of (-АВ-)
n
type. The necessary oligomers could be obtained
by means of either condensation reactions or usual polymerization. The
end groups of monomer taken in excess are responsible for the chemical
nature of process in case of condensation.
Until now, the morphological studies have been performed mainly on
block-copolymers containing two chemically different blocks
A
and
B
only. One can expect the revelation of quite novel morphological struc-
tures for three-block copolymers, including three mutually incompatible
units (
ABC
)
n
. And there are few references on such polymers.
