摘要
多面齐聚物倍半硅氧烷(POSS)是一种新型的有机-无机杂化材料,因其高的热稳定性、阻燃性、机械性能和低的介电常数,使其在聚合物/POSS复合材料中具有广泛的应用前景。
本论文通过分子设计,利用氨基POSS与丙烯酸的缩合反应合成了丙烯酸修饰POSS (AC-POSS)。然后以AIBN为引发剂,利用AC-POSS与甲基丙烯酸液晶单体的自由基共聚反应,合成了液晶高分子/POSS共聚物(LCP-POSS),并通过FT-IR和1H NMR确认了产物的化学结构。研究LCP-POSS溶液的紫外光致异构行为,发现随着紫外光照时间增加,LCP-POSS的偶氮基元发生由反式向顺式构型的转变,其吸光强度逐渐降低。LCP和LCP-POSS的光致异构化反应均表现为一级动力学,但POSS引入LCP基体中,由于其空间位阻效应,降低了偶氮苯基元的反-顺异构化速率常数。研究LCP-POSS的液晶行为发现,随POSS的含量逐渐增加,LCP-POSS液晶相变温度增加,偏振光下的液晶织构逐渐变小;而进一步增加POSS含量,将使LCP-POSS液晶性逐渐消失。这是由于POSS的空间位阻效应,降低了聚合物链的柔顺性和改变构象的能力,使LCP分子堆砌规整性降低,无序度增加,使液晶分子液晶性表现为随POSS含量增加而渐弱的趋势。
Polyhedral oligomeric silsesquioxane (POSS) as a novel organic-inorganic hybrid has many potential applications in polymers/POSS composites due to its high thermal stability, flame retardation, and mechanical properties as well as low dielectric constant.
The acrylic acid modified POSS (AC-POSS) has been synthesized by the reaction of POSS containing amine groups with acrylic acid. A free radical polymeraztion was applied to synthesize liquid crystalline polymers (LCP)/POSS copolymer (LCP-POSS) in the presence of AC-POSS and liquid crystalline monomers using AIBN as an initiator. And the chemical structures of the above products were confirmed by FT-IR and NMR spectra. The trans-isomers of azobenzene moieties in LCP-POSS were gradually transformed to cis-isomers with increasing the UV-irradiation time, accompanied by a decrease in the absorbance. LCPs and LCP-POSS showed the first-order photoisomerization reaction. As compared with the LCPs, the photoisomerization rate constant of LCP-POSS decreases due to the incorporation of the POSS as rigid segment. The phase transition temperature of liquid crystalline in LCP-POSS increases with the content of POSS, and the size of liquid crystalline domain in LCP-POSS decrescs. As the POSS content in LCP-POSS further increases, the ordered structure of liquid crystalline phase is gradually destroyed, resulting in the final disappearance of LCPs’liquid crystllinity due to the rigidity of POSS.
引文
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