Chemistry Reference
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strain. Unlike biphenyl containing macrocycles the macrocycles
BIISO
and
LIISO
are not strained at all as shown from the calculations. Apparently,
isophthaloyl moiety is not large enough to cause any significant strain in these
molecules. It follows from the results of molecular modeling the macrocycles
most active in ROP are
LI2Bph
and
LI4Bph
while
BIISO
, and
LIISO
are much
less active in ROP.
3.3. ROP of macrocycles
The polymerization of synthesized macrocycles was carried out in the molten
state at 260-270°C for 2.5 hrs under a nitrogen flow. Both biphenyl containing
macrocycles (
) readily underwent ROP producing corre-
sponding polymers (Scheme 4). Both
LI2Bph
and
LI4Bph
produce
polymers insoluble in common organic solvents which made it impossible to
measure their molecular weights. However, both polymers (
LI2Bph
and
LI4Bph
macrocycles
PLI2Bph
and
PLI4Bph
) can be processed from the melt at 280°C into strong fibers proving the
high molecular weight of the polymers obtained. The structure of the polymers
can easily be confirmed by a comparison of monomer and polymer FT-IR spectra
(Fig. 8). The FT-IR spectra are very much alike in the region of functional groups
(above 1500 cm
-1
) for both polymers and monomers differing only in the low fre-
quency region due to conformational changes in polymers. Unlike
LI2Bph
and
LI4Bph
macrocycles,
LIISO
and
BIISO
produced soluble products on polymeri-
zation. In case of
only low molecular weight soluble polymer with M
w
of
4000 and polydispersity of 1.7 was obtained together with a large amount of un-
reacted monomer (60%). The
1
H-NMR and FT-IR spectra (Fig. 9) confirm the
structure of the polymer.
It is noteworthy that
LIISO
BIISO
did not polymerize at all under the experimental
conditions.
was almost quantitatively isolated after the polymerization. As
can be seen that there is a direct correlation between the polymerizability of mac-
rocycles with calculated ring strain showing that the driving force for ROP of syn-
thesized macrocycles is the strain release and not an entropy gain during the ring
opening.
The thermal properties of synthesized polymers are listed in Table 3. Only
PLI2Bph
BIISO
is crystalline showing a melting endotherm above 200°C, while others
are amorphous as follows from DSC data showing only T
g
in the range of 75-
130°C.
Low T
g
of
BLIISO
is probably attributed to its low molecular weight, while
the crystallinity of
is due to rigid-rod character of 4,4'-diphenyl moiety
in this polymer. Due to the presence of aliphatic spacers the thermostability of the
polymers is not very impressive.
LI4Bph
LI4Bph
shows the highest 10% weight loss
temperature of 360°C (Table 3).
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