TP-rigidified main-chains acting as the columns, when the MW is higher than the
threshold value (2.3 Â 10
4 Da). PTP6-6-MA exhibits a Col h phase, dominated by TP
unit self-assembling, and no obvious MW dependence is observed, in contrast to the
inability of PTP5-11-MA to form a mesophase.
PP12V, also depicted in Chart 7, is a polymer that combines the π-stack-forming
TP units with self-compacting poly[di(n-alkyl)vinylterephthalates]. With such a
structure, there are two possible pathways for a columnar LC phase to form. At
high temperatures (>150
C), where the entropy has a greater influence, the whole
polymer chains act as cylinders and organize in a columnar nematic phase, probably
behaving as self-compacting chains. This is supported by the appearance of the
isotropic phase when cooling the columnar nematic phase to around 150
C. Further
cooling the isotropic phase to ~130
C, a Col h phase appears, driven by the
formation of TP π-stacks (Zhu et al. 2014).
Ring-opening metathesis polymerization has been employed to prepare monodispersed TP-functionalized poly(norbornene)s (PTPNB-m) and poly(butadiene)s
(PTPBD-m) with the structures shown in Chart 7. It has been shown that both
PTPNB-10 and PTPBD-10 form a disordered Col h phase without obvious π-stacking
order and very low clearing point, while PTPNB-5 and PTPBD-5 are amorphous.
Hydrogenation of the polybutadiene main-chain (leads to the formation of PTPE-m)
does not significantly affect the stability of the mesophase (Weck et al. 1997).
PTPA-m (Yu et al. 2013) and PTPOA-m (Xing et al. 2008) are TP-functionalized
polyacetylenes. PTPA-1 and PTPA-3, with short spacers, form a Col h phase that
consists of cylindrical chains having TP units jacketing around the polyacetylene
main-chain. In contrast, with a much longer spacer, the TP π-stacking dominated the
self-assembly of PTPOA-m in their Col h phase.
Column-forming TP side-units and layer-forming poly(3-alkylthiophenes) are
combined together in (PT 5 T) n , (PT 10 T) n , and (PT 15 T) n (Tahar-Djebbar et al. 2011;
Zeng et al. 2014). (PT 10 T) n and (PT 15 T) n show a rectangular lamello-columnar
mesophase. The lamellar order arises from the phase separation of rigid polythiophene backbones from the matrix and columnar order arising from π-stacking
of TP units, with TP columns parallel to the polymer backbone direction. Similarly,
(PT 5 T) n can also organize into a mesophase with a lamello-columnar order. However, the 2D order in the phase is of short range; therefore, the phase can be assigned
as a lamello-columnar nematic phase.
Columnar LC Phase-Forming Polymers with Pendent Tapered
Minidendrons
Although tapered minidendrons are not discotics, they can be considered as columnar mesogens as many of them are capable of forming a columnar mesophase (Rosen
et al. 2009).
A Col h phase has been observed in PEI-m, a series of poly/oligoethyleniminesbearing tapered minidendron side-groups (Fischer et al. 1995; Seitz et al. 1996;
Percec et al. 2001). The general structure of PEI-m and MW-dependent clearing
point of the Col h phase of PEI-8 are shown in Fig. 8. Such a weak MW dependence
of the clearing point, along with the practically MW independent Col h lattice
5 Columnar Phase-Forming Polymers
135
threshold value (2.3 Â 10
4 Da). PTP6-6-MA exhibits a Col h phase, dominated by TP
unit self-assembling, and no obvious MW dependence is observed, in contrast to the
inability of PTP5-11-MA to form a mesophase.
PP12V, also depicted in Chart 7, is a polymer that combines the π-stack-forming
TP units with self-compacting poly[di(n-alkyl)vinylterephthalates]. With such a
structure, there are two possible pathways for a columnar LC phase to form. At
high temperatures (>150
C), where the entropy has a greater influence, the whole
polymer chains act as cylinders and organize in a columnar nematic phase, probably
behaving as self-compacting chains. This is supported by the appearance of the
isotropic phase when cooling the columnar nematic phase to around 150
C. Further
cooling the isotropic phase to ~130
C, a Col h phase appears, driven by the
formation of TP π-stacks (Zhu et al. 2014).
Ring-opening metathesis polymerization has been employed to prepare monodispersed TP-functionalized poly(norbornene)s (PTPNB-m) and poly(butadiene)s
(PTPBD-m) with the structures shown in Chart 7. It has been shown that both
PTPNB-10 and PTPBD-10 form a disordered Col h phase without obvious π-stacking
order and very low clearing point, while PTPNB-5 and PTPBD-5 are amorphous.
Hydrogenation of the polybutadiene main-chain (leads to the formation of PTPE-m)
does not significantly affect the stability of the mesophase (Weck et al. 1997).
PTPA-m (Yu et al. 2013) and PTPOA-m (Xing et al. 2008) are TP-functionalized
polyacetylenes. PTPA-1 and PTPA-3, with short spacers, form a Col h phase that
consists of cylindrical chains having TP units jacketing around the polyacetylene
main-chain. In contrast, with a much longer spacer, the TP π-stacking dominated the
self-assembly of PTPOA-m in their Col h phase.
Column-forming TP side-units and layer-forming poly(3-alkylthiophenes) are
combined together in (PT 5 T) n , (PT 10 T) n , and (PT 15 T) n (Tahar-Djebbar et al. 2011;
Zeng et al. 2014). (PT 10 T) n and (PT 15 T) n show a rectangular lamello-columnar
mesophase. The lamellar order arises from the phase separation of rigid polythiophene backbones from the matrix and columnar order arising from π-stacking
of TP units, with TP columns parallel to the polymer backbone direction. Similarly,
(PT 5 T) n can also organize into a mesophase with a lamello-columnar order. However, the 2D order in the phase is of short range; therefore, the phase can be assigned
as a lamello-columnar nematic phase.
Columnar LC Phase-Forming Polymers with Pendent Tapered
Minidendrons
Although tapered minidendrons are not discotics, they can be considered as columnar mesogens as many of them are capable of forming a columnar mesophase (Rosen
et al. 2009).
A Col h phase has been observed in PEI-m, a series of poly/oligoethyleniminesbearing tapered minidendron side-groups (Fischer et al. 1995; Seitz et al. 1996;
Percec et al. 2001). The general structure of PEI-m and MW-dependent clearing
point of the Col h phase of PEI-8 are shown in Fig. 8. Such a weak MW dependence
of the clearing point, along with the practically MW independent Col h lattice
5 Columnar Phase-Forming Polymers
135