【作者】 郭朝莹；

【导师】 解孝林；

【作者基本信息】 华中科技大学 ， 高分子化学与物理， 2004， 硕士

【摘要】 本文采用原位乙酰化法,分别以对羟基苯甲酸(PHB)和对氨基苯甲酸(ABA)作为介晶基元与聚对苯二甲酸丁二酯(PBT)进行熔融缩聚,合成了PBT/PHB热致液晶共聚酯和PBT/ABA热致液晶共聚酯酰胺。同时,采用原位乙酰化和熔体插层缩聚,制备了PBT40-PHB60热致液晶共聚酯(LCP)/ 蒙脱土(MMT)纳米复合材料。利用傅立叶红外吸收光谱、差示扫描量热分析、热重分析、热台偏光显微镜、原子力显微镜和小角X-射线衍射等手段对产物的结构和性质进行了表征。研究结果表明:1) 采用原位乙酰化法代替预乙酰化法,一定程度上抑制了PHB或ABA均聚链的形成,PHB刚性基元含量为20-80mol%的PBT/PHB共聚酯、ABA刚性基元含量为15-40mol%的PBT/ABA共聚酯酰胺为向列型热致性液晶。PBT/PHB液晶共聚酯和PBT/ABA液晶共聚酯酰胺均存在双玻璃化现象(Tg1和Tg2),分别对应于共聚酯中富PBT相、富PHB或ABA相区中链段的运动;其中原位乙酰化法合成共聚物的Tg1和Tg2均低于采用预乙酰化法合成共聚物的玻璃化温度。介晶基元的引入,提高了PBT/PHB液晶共聚酯、PBT/ABA液晶共聚酯酰胺的热分解温度和残留率,提高了其热稳定性。与相同PHB含量的PBT/PHB液晶共聚酯相比,PBT/ABA共聚酯酰胺的热稳定性明显高于PBT/PHB液晶共聚酯。2) 在原位乙酰化和熔体插层缩聚过程中,蒙脱土片层被完全剥离并均匀分散在聚合物基体中,形成了全剥离型的热致液晶共聚酯/蒙脱土纳米复合材料。热致液晶共聚酯/蒙脱土纳米复合材料表现出向列型液晶行为,剥离后的蒙脱土片层影响了共聚酯分子链的有序性,使其液晶微区缩小、纹影结构的向错点变得模糊。在液晶高分子链取向的诱导作用下,均匀分散的、剥离的蒙脱土片层沿剪切力场的方向取向排列。LCP/MMT纳米复合材料存在双熔融吸热峰、双结晶放热峰,分别对应于富PBT相和富PHB相区链段的熔融、结晶。由于蒙脱土与液晶共聚酯分子链之间存在强的相互作用,蒙脱土的加入,阻碍了液晶共聚酯分子链的运动和链的有序堆积,破坏了高分子链堆积的规整性,导致其熔点、结晶温度、结晶度降低。另一方面,蒙脱土起异相成核剂的作用,加快了LCP/MMT复合材料中链段相对柔顺的富PBT相的结晶速度;而富PHB相区的链段相对刚硬,蒙脱土对其<WP=4>异相成核的影响不大。此外,蒙脱土的引入,明显地提高了LCP/MMT纳米复合材料的热分解残留率。这些结果对进一步提高聚合物/蒙脱土纳米复合材料的力学性能、阻隔性能、阻燃性和耐烧蚀能具有特别重要的意义。更多还原

【Abstract】 Thermotropic poly(butylene terephthalate) (PBT)/p-hydroxybenzoic acid (PHB) copolyesters (designated as PBT/PHB) and PBT/p-aminobenzoic acid (ABA) copolyesteramides (designated as PBT/ABA) were synthesized in the melting state by in situ acetylation with PBT and PHB or ABA, respectively. At the same time, the liquid crystalline copolyester (LCP)/montmorillonite (MMT) nanocomposites were synthesized with 40 mol% PBT, 60 mol% PHB in the presence of organoclay by in situ acetylation. Their structure and properties were characterized by Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), thermogravimetry (TGA), polarized optical microscopy (POM) with hot stage, atomic force microscopy (AFM) and small angle X-ray diffraction (SAXD). Based on the experimental results, some definitive conclusions can be drawn as the following:1) Compared with the pre-acetylation process, the in-situ acetylation method is useful to restrain from the forming of long PHB or ABA blocking chains in these copolymers. PBT/PHB copolyesters containing 20-80mol% PHB, and PBT/ABA copolyesteramides containing 15-40 mol% ABA show the nematic liquid crystalline behavior. And they all have two glass transition temperatures, which are related to PBT-rich phase, PHB-rich or ABA-rich phase in the copolymers. It is worth-mentioned that Tg1 and Tg2 of the copolymer synthesized by in situ acetylation are lower than those of the copolymer synthesized by pre-acetylation. With the incorporation of the mesogenic units (PHB or ABA segments), the thermal decomposition temperature and char residue of the PBT/PHB copolyesters and the PBT/ABA copolyesteramides are greatly increased, thereby their thermal stabilities are improved. At the same content of the mesogenic units, the thermal stability of PBT/ABA copolyesteramide is better than that of PBT/PHB copolyester.2) During the in situ acetylation and melting intercalation condensation polymerization of PBT and PHB in the presence of organoclay, LCP macromolecules entered the galleries of MMT, and fully-exfoliated LCP/MMT nanocomposites are formed, and show the nematic liquid crystalline behavior. The incorporation of the exfoliated MMT layers throughout the LCP matrix results in very fine but imperfect schlieren texture, <WP=6>and the disinclination becomes blurred. Under the induction of LCP, the exfoliated MMT layers can be oriented along the force field. Moreover, the LCP/MMT nanocomposites have two melting points and two crystallization temperatures, which are related to the melting and crystallization of the PBT-rich and PHB-rich domains in LCP macromolecules. Due to the strong interaction between LCP and exfoliated MMT layers, the exfoliated MMT layers restrain the motion activity and orderly packing of LCP, and destroy the packing regularity of LCP chains, these results lead to the decreasing in the melting points, crystallization temperatures and the degree of the crystallinity of LCP in LCP/MMT nanocomposites. In the other hand, the exfoliated MMT layers act as a heterogeneous nucleating agent, enhance the crystallization rate of PBT-rich phases in LCP/MMT nanocomposites. However, the effect of the exfoliated MMT layers is small on the crystallization rate of PHB-rich phases in LCP/MMT nanocomposites. In addition, the incorporation of the exfoliated MMT layers obviously increases the char residue of LCP/MMT nanocomposites. These results are very important to further improve the mechanical, barrier, flame-retardant and ablative properties of polymer/MMT nanocomposites.更多还原