with the better tensile strength and modulus of the composites. This behavior is
mainly due to the fibrillation of TLCP, which participate and transform the applied
stress due to its inherent strength and stiffness. Also, it is reported that the breakage
of materials mostly occurred on the interfaces between the dispersed phase and
matrix, and the larger interface area is, the more additional energy is needed
(Parameswaran and Shukla 2000).
Continuatively, by injection molding, Du and her co-workers prepared of
PET/PLCP Ar3:1 in situ reinforced composites (Du et al. 2005, 2006). The results
suggested in situ reinforcement could also be obtained by injection molding, that
tensile strength increased by at least 25% when the amount of PLCP Ar3:1 reached
8 wt%. However, the reinforcement of the injection molded sample is not as good as
that of the spinning one, which is due to the larger drawing ratio of the latter one.
Deng and his co-workers investigated the flame-retardant mechanism of PLCP Ar3:1
on PET (Deng et al. 2008). The results revealed that the presence of PLCP Ar3:1
promoted char formation of PET and enhanced thermal stability of the charring
residue, hence delayed the further decomposition of the composite. Elemental
distribution in gaseous products, liquid products, and solid residues after pyrolysis
showed that phosphorus mainly existed in liquid products and residues during
pyrolysis of both PLCP Ar3:1 and the relevant composite, rather than in gaseous
products, indicating that the main action was in the condensed phase.
Consequently, PLCP Ar endowed both good flame retardance and better mechanical properties simultaneously to the in situ composite; however, due to the high
rigidity of the main chain (wholly aromatic) and the presence of the bulky pendent
substituent on the hydroquinone unit, T g , nematic transition temperature (T LC ), and
T i of the copolyesters were very high (Table 1). Therefore, further studies have been
investigated on reducing the transition temperatures as well as expanding the
application fields of TLCP with high flame retardance.
Introducing Flexible Spacers
Introducing flexible spacers, including alkyl, silicone, and ether linkages, is supposed to increase the chain flexibility/mobility and thus to decrease the transition
temperature of such polymers. By introducing ethylene glycol-containing flexible
spacers into the mesogenic chains of PLCP Ar , Zhao and his co-workers synthesized a
phosphorus-containing TLCP named P-TLCP-FS (Scheme 3), where T LC decreased
from 290
C of the aforementioned PLCP Ar to 205
C (Zhao et al. 2008). Moreover,
P-TLCP-FS exhibited low and wide mesophase temperature, ranging from 185 to
330
C (Table 2), which could match the processing temperatures of commonly used
engineering polymers. Also due to the phosphorus-containing groups, high flame
retardance with a limiting oxygen index (LOI) value of 70 vol% and an Underwriters
Laboratories 94 (UL-94) V-0 rating could still be maintained, suggesting the potential application for flame-retardant in situ composites.
Vlad-Bubulac et al. investigated a series of phosphorus-containing liquid crystalline copolyesters based on terephthaloyl-bis-(4-oxybenzoylchloride) (TOBC),
where two preformed ester groups were incorporated as mesogenic unit, and
DOPO-substituent 1,4-naphthoquinone (DOPO-NQ) was utilized as phosphorus20 Highly Flame-Retardant Liquid Crystalline Polymers
557
mainly due to the fibrillation of TLCP, which participate and transform the applied
stress due to its inherent strength and stiffness. Also, it is reported that the breakage
of materials mostly occurred on the interfaces between the dispersed phase and
matrix, and the larger interface area is, the more additional energy is needed
(Parameswaran and Shukla 2000).
Continuatively, by injection molding, Du and her co-workers prepared of
PET/PLCP Ar3:1 in situ reinforced composites (Du et al. 2005, 2006). The results
suggested in situ reinforcement could also be obtained by injection molding, that
tensile strength increased by at least 25% when the amount of PLCP Ar3:1 reached
8 wt%. However, the reinforcement of the injection molded sample is not as good as
that of the spinning one, which is due to the larger drawing ratio of the latter one.
Deng and his co-workers investigated the flame-retardant mechanism of PLCP Ar3:1
on PET (Deng et al. 2008). The results revealed that the presence of PLCP Ar3:1
promoted char formation of PET and enhanced thermal stability of the charring
residue, hence delayed the further decomposition of the composite. Elemental
distribution in gaseous products, liquid products, and solid residues after pyrolysis
showed that phosphorus mainly existed in liquid products and residues during
pyrolysis of both PLCP Ar3:1 and the relevant composite, rather than in gaseous
products, indicating that the main action was in the condensed phase.
Consequently, PLCP Ar endowed both good flame retardance and better mechanical properties simultaneously to the in situ composite; however, due to the high
rigidity of the main chain (wholly aromatic) and the presence of the bulky pendent
substituent on the hydroquinone unit, T g , nematic transition temperature (T LC ), and
T i of the copolyesters were very high (Table 1). Therefore, further studies have been
investigated on reducing the transition temperatures as well as expanding the
application fields of TLCP with high flame retardance.
Introducing Flexible Spacers
Introducing flexible spacers, including alkyl, silicone, and ether linkages, is supposed to increase the chain flexibility/mobility and thus to decrease the transition
temperature of such polymers. By introducing ethylene glycol-containing flexible
spacers into the mesogenic chains of PLCP Ar , Zhao and his co-workers synthesized a
phosphorus-containing TLCP named P-TLCP-FS (Scheme 3), where T LC decreased
from 290
C of the aforementioned PLCP Ar to 205
C (Zhao et al. 2008). Moreover,
P-TLCP-FS exhibited low and wide mesophase temperature, ranging from 185 to
330
C (Table 2), which could match the processing temperatures of commonly used
engineering polymers. Also due to the phosphorus-containing groups, high flame
retardance with a limiting oxygen index (LOI) value of 70 vol% and an Underwriters
Laboratories 94 (UL-94) V-0 rating could still be maintained, suggesting the potential application for flame-retardant in situ composites.
Vlad-Bubulac et al. investigated a series of phosphorus-containing liquid crystalline copolyesters based on terephthaloyl-bis-(4-oxybenzoylchloride) (TOBC),
where two preformed ester groups were incorporated as mesogenic unit, and
DOPO-substituent 1,4-naphthoquinone (DOPO-NQ) was utilized as phosphorus20 Highly Flame-Retardant Liquid Crystalline Polymers
557