| A series of styrene analogues containing different length and number of terminal alkyl chains, 3,4,5-tris(alkoxy) styrene(TAVB-n), 3, 5-bis(alkoxy) styrene(DAVB-n), 4- alkoxy styrene(AVB-n), were designed and synthesized. Then we synthesized the corresponding polymers PTAVB-n, PDAVB-n and PAVB-n with relatively high molecular weight via free radical polymerization. The chemical structures, number average molecular weight(Mn) and its distribution width(PDI) and thermal stability of the above-mentioned polymers were characterized by 1H NMR, GPC and TGA. The phase behavior and phase structure of the corresponding polymers were studied by POM, DSC and 1D WAXD. The influence of different length and number of terminal alkyl chains on the phase behavior of the polymers had been invesgated.The experimental results showed that PTAVB-6 exhibited no liquid crystalline behavior, however, PTAVB-n(n = 8, 10, 12, 14, 16, 18) can form columnar phase at high temperature and the liquid crystalline phase disappeared as the temperature reduced. In other words, PTAVB-n(n = 8, 10, 12, 14, 16, 18) exhibited a re-entrant isotropic phase. It was found that the temperature when PTAVB-n formed liquid crystalline phase decreased as the length of terminal alkyl chain increased. We can conclude that the polymers can form columnar phase easier with the increasing of the expandable volume of the side groups.When the number of terminal alkoxy groups changed into 2 or 1, PDAVB-n(n = 6, 10, 14, 18) and PTAVB-n(n = 6, 10, 14, 18) became amorphous and exhibited no liquid crystalline properties as temperature changed. We believed the reason which caused the difference between PTAVB-n and PDAVB-n, PTAVB-n was the decrease of steric effect. When the steric effect of side pendant on the polymer chain decreased, the side groups can’t force the polymer chain adopted a straight conformation, that is, the polymers changed from columnar phase into amorphous on phase behavior. |
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