A series of main-chain thermotropic liquid crystalline polyesters were synthesized by polycondensation from mesogenic dial as 4,4'-bis(6-hydroxyhexyloxy)biphenyl (BHHBP) and various diacids with different substituents as succinic acid (no side group), 2-methylsuccinic acid (aliphatic side group) and 2phenylsuccinic acid (aromatic side group), named as poly(4,4'-bis(6-hydroxyhexyloxy)biphenyl succinate) (PBDS), poly(4,4'-bis(6-hydroxyhexyloxy)biphenyl methylsuccinate) (PBDMS), poly(4,4'-10 bis(6-hydroxyhexyloxy)biphenyl phenylsuccinate) (PBDPS), respectively. Liquid crystalline behaviours were investigated through differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and small angle scattering (SAXS) and thermal stability of the polyesters was determined via thermogravimetric analysis (TGA). PBDS, PBDMS and PBDPS showed a SmF, SmB and SmA phase, respectively. With enlarging the side group, the d-spacing of the smectic layer increased, indicating a 15 folding packing of the polymer chains. Therefore, the adjacent phenyl rings in side groups stacked well together and formed strong π-π interaction even when the temperature was higher than T i .The special structure of PBDPS could endow the good mechanical property. Thus, PBDPS had the maximum tensile stress (28.6 MPa) and the highest elongation at break (1060 %). Furthermore, the strong π-π interaction can act as netpoints, therefore, PBDPS exhibited excellent shape fixing (>99 %) and shape recovery ratio 20 (>99 %) with large strain (>220 %). 65 question may be put forward: can these π-π interactions be strong enough to act as netpoints in a shape memory liquid crystalline polymer? If the answer is positive, the structural design of TLCP is very important.
The flame retardation of polymeric materials can be achieved by addition of small-molecule flame retardants. However, traditional small molecule flame retardants exhibit practical drawbacks during application, such as migration problems, the deterioration of polymer performance, as well as potential persistence, bio-accumulation and toxicity (PBT), etc. High molecular weight molecules have been found to be less accessible by living organisms and so have an automatically lower PBT profiles than small molecules. Phosphorus-containing thermotropic liquid crystalline polymers have proven to be a class of efficient polymeric flame retardants, which can overcome the aforementioned drawbacks of small molecules and have potential industrial applications to replace some of the existing small molecule flame retardants. The recent relevant developments are reviewed in this article.
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