Molecular Architecture
In the LC phases of MJLCPs, the MJLCP supramolecular mesogens are aligned
parallel to one another. If the change in molecular architecture influences such a
parallel alignment, the phase behavior will undoubtedly be affected.
The effect of architecture was elucidated in an eight-arm star PMPCS polymer
which was synthesized by ATRP using an octafunctionalized initiator (Pan et al. 2007).
The MW of each arm for the formation of the LC phase is lower than that of
the linear PMPCS. In addition, the star polymer only exhibits the more ordered
Col hn phase. The result suggests that this molecular architecture favors the parallel
packing of PMPCS chains. On the other hand, the hyperbranched structure is unfavorable for the formation of the more ordered LC phase, as a hyperbranded
PMPCS copolymer synthesized by ATRP only shows a less ordered Col n phase
(Mei et al. 2008).
Molecular Design for MJLCPs
While the design of monomers for easier synthesis is also important, such molecular
details will not be discussed. As abovementioned, many factors affect the phase
behaviors of MJLCPs. Therefore, the molecular design for MJLCPs involves considerations on the detailed chemical structures of the backbones and side chains of
the polymers. Molecular parameters, such as the shape and rigidity of the side chain,
the structure of the polymer backbone, and so on, should be carefully selected on the
basis of the chemical structure-phase behavior relationships of MJLCPs.
In addition, the size of the structure formed by an MJLCP, either columnar or
smectic, is directly correlated with the size of the side chain. Therefore, the diameter
of the supramolecular rod or the width of the sheetlike structure can be readily tuned
by varying side chains (Chen et al. 2010).
The first MJLCPs based on polyacrylates have a short linkage between the sidechain mesogen and the main chain (Zhou et al. 1987). Later, polystyrene-based
MJLCPs were synthesized, and the side-chain mesogen was attached to the backbone with just one carbon-carbon single bond (Zhou et al. 1989). Then, many series
of polystyrene-based MJLCPs have been obtained, with flexible aliphatic tails at the
ends of the mesogenic side chains. Most of the MJLCPs exhibit stable columnar
phases. With the increase in the conjugation length or the rigidity of the side chain,
polymers showing smectic LC phases are obtained.
In the molecular design of the first MJCLPs, mesogenic side chains were used.
Different types of mesogens, including calamitic, bent-cored (Chen et al. 2006b;
Xu et al. 2009), and discotic (Yu et al. 2013) ones, have been used in the side
chains of MJLCPs. Because the liquid crystallinity of MJLCPs originates from
supramolecular mesogens owing to the “jacketing” effect, it is not necessary
to use mesogens in the side chain. Many series of MJLCPs with non-mesogenic
side groups have been designed and synthesized (Tu et al. 2000; Zhang et al.
1999). Some of these MJLCPs exhibit isotropization temperatures before decomposition (Tu et al. 1999).
2 Mesogen-Jacketed Liquid Crystalline Polymers: Molecular Design and. . .
41
In the LC phases of MJLCPs, the MJLCP supramolecular mesogens are aligned
parallel to one another. If the change in molecular architecture influences such a
parallel alignment, the phase behavior will undoubtedly be affected.
The effect of architecture was elucidated in an eight-arm star PMPCS polymer
which was synthesized by ATRP using an octafunctionalized initiator (Pan et al. 2007).
The MW of each arm for the formation of the LC phase is lower than that of
the linear PMPCS. In addition, the star polymer only exhibits the more ordered
Col hn phase. The result suggests that this molecular architecture favors the parallel
packing of PMPCS chains. On the other hand, the hyperbranched structure is unfavorable for the formation of the more ordered LC phase, as a hyperbranded
PMPCS copolymer synthesized by ATRP only shows a less ordered Col n phase
(Mei et al. 2008).
Molecular Design for MJLCPs
While the design of monomers for easier synthesis is also important, such molecular
details will not be discussed. As abovementioned, many factors affect the phase
behaviors of MJLCPs. Therefore, the molecular design for MJLCPs involves considerations on the detailed chemical structures of the backbones and side chains of
the polymers. Molecular parameters, such as the shape and rigidity of the side chain,
the structure of the polymer backbone, and so on, should be carefully selected on the
basis of the chemical structure-phase behavior relationships of MJLCPs.
In addition, the size of the structure formed by an MJLCP, either columnar or
smectic, is directly correlated with the size of the side chain. Therefore, the diameter
of the supramolecular rod or the width of the sheetlike structure can be readily tuned
by varying side chains (Chen et al. 2010).
The first MJLCPs based on polyacrylates have a short linkage between the sidechain mesogen and the main chain (Zhou et al. 1987). Later, polystyrene-based
MJLCPs were synthesized, and the side-chain mesogen was attached to the backbone with just one carbon-carbon single bond (Zhou et al. 1989). Then, many series
of polystyrene-based MJLCPs have been obtained, with flexible aliphatic tails at the
ends of the mesogenic side chains. Most of the MJLCPs exhibit stable columnar
phases. With the increase in the conjugation length or the rigidity of the side chain,
polymers showing smectic LC phases are obtained.
In the molecular design of the first MJCLPs, mesogenic side chains were used.
Different types of mesogens, including calamitic, bent-cored (Chen et al. 2006b;
Xu et al. 2009), and discotic (Yu et al. 2013) ones, have been used in the side
chains of MJLCPs. Because the liquid crystallinity of MJLCPs originates from
supramolecular mesogens owing to the “jacketing” effect, it is not necessary
to use mesogens in the side chain. Many series of MJLCPs with non-mesogenic
side groups have been designed and synthesized (Tu et al. 2000; Zhang et al.
1999). Some of these MJLCPs exhibit isotropization temperatures before decomposition (Tu et al. 1999).
2 Mesogen-Jacketed Liquid Crystalline Polymers: Molecular Design and. . .
41