516
S. Okada et al.
reacted. From the detailed analysis of 15 using
13 C-NMR spectra, it was clarified
that one of two hexatriyne moieties reacted to form the single-chain polydiacetylene. The 1,4-polymerization sites were found to be at the first acetylenic carbon
next to the methylene chain and the fourth acetylenic carbon from the methylene
chain, i.e., polydiacetylene substituted by 2-[4-(hexatriynyl)phenyl]ethynyl groups
was formed. Although further polymerization was attempted on cocrystals of 13
with 12 and crystals of 14 and 15, it was hard to obtain the polymers with two
polydiacetylene backbones linked by arylene groups from these monomers.
24.4.2 Ring Monomer with Nonconjugated Linkage
As ladder polymers are obtained from linear monomers with two butadiyne moieties,
tubular polymers are expected to be formed from ring monomers with butadiyne
moieties. There were several examples of the ring monomers with one or two
butadiyne moieties [13, 52, 53]. If some parts of the ring structure are composed of
methylene chains, the resulting tubular polymers seem to be soft in contrast to rigid
tubular polymers like carbon nanotubes. Molecular inclusion ability in the polymer
tubes may show interesting phenomena such as specific molecular transport and
specific interaction between the tube wall and included molecules.
As described in Sect. 24.3, butadiyne derivatives with 3,4,5-alkyloxyphenyl
groups at ends give polydiacetylenes with nanofibrous morphology. Based on
this molecular design, synthesis of a tubular polydiacetylene was planned [54].
Compound 10 was selected as a basic structure, and one of dodecyl groups on
the phenyl rings was converted to the nonylene linkage by design to connect two
butadiyne derivatives, resulting in a ring monomer 16 (Fig. 24.12). It was actually
synthesized by the copper-catalyzed oxidative coupling reaction of the precursor
17 (Fig. 24.12). The structure of 16, purified finally by the gel permeation chromatography, was confirmed by the following features. In the
1 H-NMR spectrum, the
terminal acetylene protons were not detected. Although aromatic protons of 17 were
observed at the same chemical shift due to free rotation of the aromatic ring, those
of 16 were observed as a pair of doublet peaks suggesting the fixed ring structure.
The MALDI-TOF mass spectrum clearly indicated existence of the species with the
molecular weight corresponding to 16. Interestingly, in spite of similar molecular
weights, melting point of 16 is much higher than that of 17, i.e., 153.5 and 107.3 °C,
respectively.
Cyclic compound 16 was found to crystallize in two modifications I and II. It is
not surprising because 10 as the basic structure also showed more than one crystalline forms. Modification I solidified from chloroform-methanol mixture showed
the absorption bands around 500 nm characteristic of polydiacetylene upon UV irradiation. In contrast, absorption changes of modification II solidified from chloroformhexane mixture were similar to those displayed in Fig. 24.3b indicating irregular
polymerization. When the solution of 16 in chloroform-methanol mixture was dropcasted and dried, the nanofibrous structures with the diameter of 80 ± 30 nm like in
S. Okada et al.
reacted. From the detailed analysis of 15 using
13 C-NMR spectra, it was clarified
that one of two hexatriyne moieties reacted to form the single-chain polydiacetylene. The 1,4-polymerization sites were found to be at the first acetylenic carbon
next to the methylene chain and the fourth acetylenic carbon from the methylene
chain, i.e., polydiacetylene substituted by 2-[4-(hexatriynyl)phenyl]ethynyl groups
was formed. Although further polymerization was attempted on cocrystals of 13
with 12 and crystals of 14 and 15, it was hard to obtain the polymers with two
polydiacetylene backbones linked by arylene groups from these monomers.
24.4.2 Ring Monomer with Nonconjugated Linkage
As ladder polymers are obtained from linear monomers with two butadiyne moieties,
tubular polymers are expected to be formed from ring monomers with butadiyne
moieties. There were several examples of the ring monomers with one or two
butadiyne moieties [13, 52, 53]. If some parts of the ring structure are composed of
methylene chains, the resulting tubular polymers seem to be soft in contrast to rigid
tubular polymers like carbon nanotubes. Molecular inclusion ability in the polymer
tubes may show interesting phenomena such as specific molecular transport and
specific interaction between the tube wall and included molecules.
As described in Sect. 24.3, butadiyne derivatives with 3,4,5-alkyloxyphenyl
groups at ends give polydiacetylenes with nanofibrous morphology. Based on
this molecular design, synthesis of a tubular polydiacetylene was planned [54].
Compound 10 was selected as a basic structure, and one of dodecyl groups on
the phenyl rings was converted to the nonylene linkage by design to connect two
butadiyne derivatives, resulting in a ring monomer 16 (Fig. 24.12). It was actually
synthesized by the copper-catalyzed oxidative coupling reaction of the precursor
17 (Fig. 24.12). The structure of 16, purified finally by the gel permeation chromatography, was confirmed by the following features. In the
1 H-NMR spectrum, the
terminal acetylene protons were not detected. Although aromatic protons of 17 were
observed at the same chemical shift due to free rotation of the aromatic ring, those
of 16 were observed as a pair of doublet peaks suggesting the fixed ring structure.
The MALDI-TOF mass spectrum clearly indicated existence of the species with the
molecular weight corresponding to 16. Interestingly, in spite of similar molecular
weights, melting point of 16 is much higher than that of 17, i.e., 153.5 and 107.3 °C,
respectively.
Cyclic compound 16 was found to crystallize in two modifications I and II. It is
not surprising because 10 as the basic structure also showed more than one crystalline forms. Modification I solidified from chloroform-methanol mixture showed
the absorption bands around 500 nm characteristic of polydiacetylene upon UV irradiation. In contrast, absorption changes of modification II solidified from chloroformhexane mixture were similar to those displayed in Fig. 24.3b indicating irregular
polymerization. When the solution of 16 in chloroform-methanol mixture was dropcasted and dried, the nanofibrous structures with the diameter of 80 ± 30 nm like in