Synthesis And Phase Behaviors Of Side-chain Liquid Crystalline Polymers Bearing Azobenzene Mesogen With The Different Tail Length

Side-chain liquid crystalline polymers （SCLCPs） bearing azobenzene mesogenhave attracted considerable interest for their potential application in numerous areassuch as nonlinear optical materials and optical information storage devices.The molecular architecture of SCLCPs consists of four parts: the main chain, theflexible spacer, the mesogenic unit and the terminal group. The terminal group has agreat influence on the phase behavior of SCLCPs, containing the type and length ofthe terminal group. This paper maily focused on studying the effection of the taillength on the phase behaviors of SCLCPs.1. A series of monomers (PMAzoCOOR_n+1。,6-[4-（4-phenoxyl） azobenzoic acidester with different terminal length were designed and synthesized. The molecularstructure of these monomers was characterized with1H NMR and MALDI-TOF. Thephase behavior was investigated by DSC and POM. The results have shown that withthe growth of the tail length, the liquid crystal phase of monomers was changed fromnematic phase to smectic phase; the clearing point decreased with increasing taillength and then increased with further increasing of alkyl length; however, the variedof the melt point of monomers was not clear.2. The corresponding polymers PMAzoCOORn+1were synthesized via freeradical polymerization. These polymers were confirmed by¹H NMR and GPC. Allpolymers showed good thermal stability and exhibited smectic phase. ButPMAzoCOOR₂, PMAzoCOOR₃, PMAzoCOOR₄showed a transition from thesmectic phases to the other smectic phase. With the increased of tail length, the trendof clearing point was the same to the monomers; but the change law of the influenceof tail length on glass transition temperature was not clear.