Discotic Side-Chain Polymers
Discotic side-chain polymers are the most studied class of discotic polymers, having
discotic mesogens as a pendent group on the polymeric backbone. These pendent
groups can be attached to the polymer backbone mainly by two methods. First
method involves the polymer substitution reaction between already synthesized
polymer and discotic mesogens, and in second method, discotic mesogens are
functionalized to achieve such monomers having polymerizable groups.
Discotic Side-Chain Polymers Based on Alkynylbenzene
Alkynylbenzene has a natural tendency to form nematic mesophase, which if
incorporated with polymer backbone can lead to suppressed crystallization of the
polymer backbone. It can also help to achieve the low-temperature liquid crystalline
polymers with a broader mesophase range. A series of radial pentyne-based sidechain polyacrylate have been synthesized by Kouwer et al. (2002a, b, 2003). The
synthesis process involved the polymer substitution reaction between hydroxylterminated radial pentaalkynylbenzene derivative 37 and polyacryloyl chloride 36,
in the presence of pyridine and catalytic amount of DMAP in dry dichloromethane
followed by quenching with excess methanol as shown in Scheme 8.
Both the polymers 38.1 and 38.7 were found to be non-mesomorphic; however,
connecting the lateral alkyl chains with oxygen instead of methylene induces a
nematic phase in the polymers 38.2–38.6. Polymers with short alkoxy peripheral
groups 38.4–38.6 decompose at higher temperature before reaching the isotropic
phase, whereas polymer with long alkoxy chains have lower isotropic temperature
Table 8 Phase behavior of cyclotetraveratrylene-based main-chain polymers (Ref 17: Percec et al.
1992)
Mesogen R
n
Ratio between
32 and 33
Phase behavior
34.1
C 6 H 13 12 6:1
g 15 Col 102 Col 120 Col h 145 I
34.2
C 6 H 13 12 4:1
g 18 Col 99 Col 120 Col h 139 I
34.3
C 6 H 13 12 3:1
g 20 Col 98 Col 120 Col h 136 I
34.4
C 6 H 13 12 2:1
g 20 Col 95 Col h 118 I
34.5
C 7 H 15 12 6:1
Col 90 Col 103 Col 116 Col h 141 I
34.6
C 7 H 15 12 4:1
Col 103 Col 114 Col h 139 I
34.7
C 7 H 15 12 3:1
Col 64 Col 92 Col h 110 I
34.8
C 7 H 15 12 2:1
Col 89 Col h 103 I
34.9
C 7 H 15 16 6:1
g 14 Col 90 Col 105 Col 120 Col h 127 Col h 142 I
34.10
C 7 H 15 16 4:1
g 18 Col 87 Col 103 Col 117 Col h 134 I
34.11
C 7 H 15 16 3:1
g 18 Col 86 Col 102 Col 112 Col h 129 I
34.12
C 7 H 15 16 2:1
g 19 Col 83 Col 99 Col 107 Col h 122 I
34.13
C 7 H 15 16 3:2
g 20 Col h 102 I
74
S. Setia et al.
Discotic side-chain polymers are the most studied class of discotic polymers, having
discotic mesogens as a pendent group on the polymeric backbone. These pendent
groups can be attached to the polymer backbone mainly by two methods. First
method involves the polymer substitution reaction between already synthesized
polymer and discotic mesogens, and in second method, discotic mesogens are
functionalized to achieve such monomers having polymerizable groups.
Discotic Side-Chain Polymers Based on Alkynylbenzene
Alkynylbenzene has a natural tendency to form nematic mesophase, which if
incorporated with polymer backbone can lead to suppressed crystallization of the
polymer backbone. It can also help to achieve the low-temperature liquid crystalline
polymers with a broader mesophase range. A series of radial pentyne-based sidechain polyacrylate have been synthesized by Kouwer et al. (2002a, b, 2003). The
synthesis process involved the polymer substitution reaction between hydroxylterminated radial pentaalkynylbenzene derivative 37 and polyacryloyl chloride 36,
in the presence of pyridine and catalytic amount of DMAP in dry dichloromethane
followed by quenching with excess methanol as shown in Scheme 8.
Both the polymers 38.1 and 38.7 were found to be non-mesomorphic; however,
connecting the lateral alkyl chains with oxygen instead of methylene induces a
nematic phase in the polymers 38.2–38.6. Polymers with short alkoxy peripheral
groups 38.4–38.6 decompose at higher temperature before reaching the isotropic
phase, whereas polymer with long alkoxy chains have lower isotropic temperature
Table 8 Phase behavior of cyclotetraveratrylene-based main-chain polymers (Ref 17: Percec et al.
1992)
Mesogen R
n
Ratio between
32 and 33
Phase behavior
34.1
C 6 H 13 12 6:1
g 15 Col 102 Col 120 Col h 145 I
34.2
C 6 H 13 12 4:1
g 18 Col 99 Col 120 Col h 139 I
34.3
C 6 H 13 12 3:1
g 20 Col 98 Col 120 Col h 136 I
34.4
C 6 H 13 12 2:1
g 20 Col 95 Col h 118 I
34.5
C 7 H 15 12 6:1
Col 90 Col 103 Col 116 Col h 141 I
34.6
C 7 H 15 12 4:1
Col 103 Col 114 Col h 139 I
34.7
C 7 H 15 12 3:1
Col 64 Col 92 Col h 110 I
34.8
C 7 H 15 12 2:1
Col 89 Col h 103 I
34.9
C 7 H 15 16 6:1
g 14 Col 90 Col 105 Col 120 Col h 127 Col h 142 I
34.10
C 7 H 15 16 4:1
g 18 Col 87 Col 103 Col 117 Col h 134 I
34.11
C 7 H 15 16 3:1
g 18 Col 86 Col 102 Col 112 Col h 129 I
34.12
C 7 H 15 16 2:1
g 19 Col 83 Col 99 Col 107 Col h 122 I
34.13
C 7 H 15 16 3:2
g 20 Col h 102 I
74
S. Setia et al.