monomer was lower compared to that of the first-generation monomer, possibly
owing to a lower concentration of the double bond and a stronger steric hindrance of
the former. Nevertheless, these three types of polymers with quite bulky side groups
all display LC behaviors. It should be noted that the polymers with Tp moieties are
MCSCLCPs based on an MJLCP backbone because Tp is a typical discotic mesogen. The length of the spacer between the Tp units and the side-chain core plays an
important role in regulating the competitive and synergetic interactions of the two
different types of mesogens, the MJLCP backbone and the Tp discotic mesogen in
the side chain, and determining the phase behavior of this PPnV MCSCLCP. For
PnPOSS, the phase behavior is also dependent on the length of the spacer between
the crystalline POSS units and the side-chain core.
Controlled Radical Polymerization
Although most MJLCPs can be easily polymerized from vinyl monomers using
conventional free radical polymerizations, the resulting polymers usually have broad
MWDs, which is not favorable for the study of relationships between LC phase
behaviors and chemical structures. Owing to the presence of functional groups in the
side chains of most MJLCPs, commonly used controlled/living polymerization
methods such as anionic polymerization cannot be employed. However, the rapid
development in controlled radical polymerizations, such as nitroxide-mediated radical polymerization (NMRP) and ATRP, makes it possible to synthesize MJLCPs
with controlled MWs and MWDs (Chen et al. 2010; Gao et al. 2009).
Nitroxide-Mediated Radical Polymerization (NMRP)
Ober et al. applied NMRP or stable free radical polymerization (SFRP) in the
synthesis of MJLCPs. The styrenic monomer 2,5-bis[(4-butylbenzoyl)oxy]styrene
(BBOS) polymerizes much faster than styrene in bulk polymerization (Pragliola
et al. 1999), which can be attributed to the presence of the LC phase, steric factors,
and electronic effect of the acetoxy groups (Gopalan and Ober 2001).
PnPOSS (n = 6, 10)
Si
O
Si
O
Si
O
Si
O
Si
O
Si
O
Si
O
Si
O
O
O
O
O
O
O
O
O
O
O H 2n C n
S
i
O
Si
O
Si
O
Si
O
S
i
O
S
i
O
Si
O
Si
O
O
O
O
O
O
O
C n H 2n
x
Chart 4 Chemical structure of PnPOSS
44
Z. Shen
owing to a lower concentration of the double bond and a stronger steric hindrance of
the former. Nevertheless, these three types of polymers with quite bulky side groups
all display LC behaviors. It should be noted that the polymers with Tp moieties are
MCSCLCPs based on an MJLCP backbone because Tp is a typical discotic mesogen. The length of the spacer between the Tp units and the side-chain core plays an
important role in regulating the competitive and synergetic interactions of the two
different types of mesogens, the MJLCP backbone and the Tp discotic mesogen in
the side chain, and determining the phase behavior of this PPnV MCSCLCP. For
PnPOSS, the phase behavior is also dependent on the length of the spacer between
the crystalline POSS units and the side-chain core.
Controlled Radical Polymerization
Although most MJLCPs can be easily polymerized from vinyl monomers using
conventional free radical polymerizations, the resulting polymers usually have broad
MWDs, which is not favorable for the study of relationships between LC phase
behaviors and chemical structures. Owing to the presence of functional groups in the
side chains of most MJLCPs, commonly used controlled/living polymerization
methods such as anionic polymerization cannot be employed. However, the rapid
development in controlled radical polymerizations, such as nitroxide-mediated radical polymerization (NMRP) and ATRP, makes it possible to synthesize MJLCPs
with controlled MWs and MWDs (Chen et al. 2010; Gao et al. 2009).
Nitroxide-Mediated Radical Polymerization (NMRP)
Ober et al. applied NMRP or stable free radical polymerization (SFRP) in the
synthesis of MJLCPs. The styrenic monomer 2,5-bis[(4-butylbenzoyl)oxy]styrene
(BBOS) polymerizes much faster than styrene in bulk polymerization (Pragliola
et al. 1999), which can be attributed to the presence of the LC phase, steric factors,
and electronic effect of the acetoxy groups (Gopalan and Ober 2001).
PnPOSS (n = 6, 10)
Si
O
Si
O
Si
O
Si
O
Si
O
Si
O
Si
O
Si
O
O
O
O
O
O
O
O
O
O
O H 2n C n
S
i
O
Si
O
Si
O
Si
O
S
i
O
S
i
O
Si
O
Si
O
O
O
O
O
O
O
C n H 2n
x
Chart 4 Chemical structure of PnPOSS
44
Z. Shen