导　　师： 朱美芳

学科专业： 070305

授予学位： 博士

作　　者： ;

机构地区： 东华大学

摘　　要： 甲壳型液晶高分子是指刚性液晶基元通过一个共价键与主链直接联接的液晶高分子,是主链型液晶高分子、侧链型液晶高分子之后的第三类新型液晶高分子。由于其分子结构的特殊性和“甲壳效应”,本来是“无规线团”的高分子链变成“线性”柱状高分子链。结构决定性能,它的许多物理性质诸如液晶性能、分子取向、流变性能、纤维成形、和独特的形状记忆性能等问题具有重要学术意义和探索的价值。本文选择聚/[乙烯基对苯二甲酸二/(对丁氧基苯/)酯/]/(PBPCS/)作为甲壳型液晶高分子上述问题的研究模型。 在PBPCS液晶行为再认识的研究中,宏量制备了PBPCS,用IR、NMR、元素分析对PBPCS进行表征。通过POM、WAXD、ARES实验考察了PBPCS热致液晶行为。在热力学和动力学分析基础上,认为熵致相变和自组装形成六方柱液晶相。同时由于柔性主链与侧链液晶基元充分的“偶合作用”,在两者相互协调和相互竞争中,会导致体系相变过程中存在各种类型亚稳定相。而稳定的液晶相关键在于柱状高分子链通过分子间缔合凝聚在一起,这种凝聚力越大,形成的液晶相越稳定。由于高温液晶相的交联结构的形成,PBPCS液晶态表现出反常而奇特的流变性、粘弹性。同时发现PBPCS具有溶致性液晶行为。 在PBPCS纤维成形性能的研究中,首先用Baleo的TIF模型理论上分析了PBPCS熔融液晶纺丝的分子取向。用二维X光衍射/(2D WAXD/)研究PBPCS初生纤维、拉伸率λ=300/%纤维、兄=500/%纤维的取向变化,纤维取向度、平均取向角θ、拉伸方向指向失n=随拉伸倍数增加而优化。其分子取向过程为,在外力作用下,将首先发生链段取向,柔性主链、液晶基元的协同运动带动整个分子链、自组装单元的进一步取向,它是通过柔性主链内旋转发生分子链构象的改变完成,在取向流动中发生形变。用Dewitt模型分析PBPCS纺丝熔体稳态剪切流动,Dewitt模型和ARES实验均表明PBPCS剪切变稀和“结构粘性”的特点,为了不破坏PBPCS自组装体结构,纺丝在较低剪切速率下进行。用Metzner模型和Lodge网络模型分析PBPCS纺丝熔体单轴拉伸流动,由于松弛时间大,纺丝在较低拉伸速率下进行。同时通过DMA、2D WAXD、SEM实验研究了PBPCS初生纤维的后拉伸,经过5倍的后拉伸,PBPCS纤维的取向度由64/%提高到85/%,拉伸强度由10Mpa提高到35Mpa,断裂伸长率由6/%提高到15/%,但由于纤维纺丝最大拉伸比的限制,2D WAXD实验表明,拉伸比为7时PBPCS自组装体分子链发生滑移,因此PBPCS初生纤维合适的后拉伸比为5。 PBPCS纤维的形状记忆性能研究表明,PBPCS纤维是在分子水平上通过自组装形成的具有极佳形状记忆性能的功能纤维,PBPCS纤维属于热触发形状记忆材料,热响应温度接近玻璃化转变温度108℃,形状回复力在1.6Mpa左右。PBPCS纤维形状回复不仅依赖于温度而且还依赖于时间,形状回复速度很慢,而且在不同情形下的形状回复曲线相似并符合指数规律,同时用Maxwell并联模型对PBPCS纤维形状记忆效应进行模拟,能很好与实验结果相吻合。为了验证PBPCS纤维形状记忆效应的重复性,对PBPCS纤维的形状记忆效应进行5次热机械循环实验测试,形变固定率达99.5/%以上,形变回复比率接近100/%,在以上实验基础上,提出PBPCS纤维形状记忆机理,PBPCS纤维大分子链中柔性主链充当开关结构,液晶基元充当固定结构,柔性主链与液晶基元比例相当,液晶相自组装形成的交联网状结构是其形状记忆效应的原因。 论文最后探讨PBPCS在高性能阻尼材料中的应用,通过原位复合技术把PBPCS分散到核壳结构的聚丙烯酸酯中制备PBPCS与IPN聚丙烯酸酯三元共混阻尼材料。由IR光谱、TEM透射电镜初步认为PBPCS被包裹在IPN聚丙烯酸酯聚合物中,但PBPCS的加入会影响到核壳粒子结构的正常形态。通过DMA实验得到耗散因子曲线表明,加入PBPCS的三元共混物在高温区的最大耗散因子提高到0.9以上,表明PBPCS在一定程度上增加IPN聚丙烯酸酯的阻尼能力,同时从三元共混物体系中分子链相对运动对这一现象做出解释。 Mesogen-jacketed liquid crystalline polymer /(MJLCP/) that the rigid mesogens directly attach to the backbone chain only through a covalent bond, is considered as the third classic novel liquid crystalline polymer /(LCP/) after main chain liquid crystalline polymers /(MCLCP/) and side chain liquid crystalline polymer /(SCLCP/). Because of its special macromolecular chain structure and the "Jacketed effect", macromolecular chain demonstrates special "linear" columnar chain characteristics not the usual "random coil" chain. As well known, the performance is determined by the structure, the physical properties of MJLCP, such as liquid crystalline /(LC/) behavior, molecular orientation, rheological properties, fiber formation, and the unique shape memory effect, are important and significant for academic research. In this paper, Poly-{2,5-bis/[/(4-butoxyphenyl/)oxycarbonyl/]styrene}, PBPCS, has been investigated as the research model of MJLCP for the above questions. In section for the in-depth investigation of PBPCS LC behavior, PBPCS was macro-prepared and characterized with IR, NMR, element analysis, PBPCS thermotropic LC behavior was investigated through POM, WAXD, ARES. On the basis of thermodynamics and kinetics, hexagonal columnar liquid crystalline phase was formed by entropy change and self-assembly. Because of the complete "coupling effect", PBPCS demonstrated various types of meta-stable phase in phase transition by the cooperation and competition between flexible backbone chain and side mesogens. The stability of liquid crystalline phase was determined by intermolecular condensed force, the greater condensed force, the more stable liquid crystalline phase. Due to the crosslinked structure formation at high-temperature LC phase, PBPCS showed abnormal rheology and viscoelasticity. At the same time, PBPCS Lyotropic LC behavior was also investigated. In section for the PBPCS fiber formation, firstly, the molecular orientation of PBPCS melt-spinning in LC phase was investigated according to Baleo TIF model in theory. The orientation varieties of the original PBPCS fiber, drawn fibers /(draw ratioλ=300/%,λ=500/%/) were investigated by two-dimensional X-ray diffraction /(2D WAXD/), orientation degree /(F/), the average orientation angleθ, the draw direction vector nz.were enhanced with the draw ratio increasing. During the drawing upon applied load, the segment orientation will be occurred firstly, then the cooperation between the flexible backbone chain and mesogens drives the orientation of the macromolecular chain and self-assembly unit. Further orientation of the macromolecular chain and self-assembly unit were completed by the conformation change through covalent bands rotation of the flexible backbone chain, and the deformation occurred at the same time. During the steady shear flow of melt spinning, Dewitt model and ARES experiments both showed shear-thinning behavior and "structural viscous" characteristics, therefore, spinning at low shear rate was performed in order not to destroy the self-assembly structure of PBPCS. During the uniaxial elongation flow of melt spinning, according to the Lodge network model and long relaxation time of PBPCS, spinning was performed at slow stretching rate. At the same time, DMA,2D WAXD, SEM were applied to investigate the post-drawing of PBPCS original fiber, after 5 times drawing treatment, the orientation degree increased from 64/% to 85/%, the tensile strength and elongation at break were improved from lOMpa to 35Mpa and from 6/% to 15/%, respectively. However, due to the limitation of maximum draw ratio,2D WAXD experiments demonstrated molecule chain slippage of self-assembly PBPCS as the draw ratio was 7, so the fiber formation of PBPCS was performed under low shear rate and slow stretching rate, the suitable post-drawing ratio is 5 In section for the shape memory effect of PBPCS fiber, self-assembly PBPCS fiber is novel shape memory material in molecular level. PBPCS fiber belonged to heat-triggered SMP that the thermo-responsive temperature was about 108℃near glass transition temperature /(Tg/), the recovery depended not only on the temperature but also the time, recovery rate was slow and recovery plots were similar under different cases, a viscoelastic model based on two Maxwell models in parallel was discussed for the shape memory behavior, recovery stress was about 1.6Mpa determined by DMA. In order to verify the repeatability of shape memory effect, cyclic thermo-mechanical tests for 5 times were performed, the results indicated that PBPCS fiber exhibited excellent shape memory effect, shape fixing ratio was above 99.5/%, shape recovery ratio was near 100/%. A reasonable mechanism was proposed, flexible backbone chains acted as switch structure, mesogens as fixing structure, and the self-assembly cross-linked network structure formed in LC phase lead to shape memory effect of PBPCS fiber. Finally, PBPCS in high-performance damping materials application was investigated, the ternary blend damping materials with MJLCP and IPN polyacrylate were prepared by situ composite through dispersing PBPCS into polyacrylate core-shell structure. MJLCP was wrapped in IPN polyacrylate according to IR and TEM experiments, however the adding PBPCS affected the normal morphology of core-shell particle. The dissipation damping factor was determined by DMA, results revealed ternary blends'maximum dissipation factor increased above 0.9 at high temperatures region because of PBPCS adding, it indicated that MJLCP can promote the damping ability of IPN polyacrylate to some extent.

关 键 词： 甲壳型液晶高分子 液晶行为 纤维成形 形状记忆效应 阻尼

分 类 号： [O753.2]

领　　域： [理学]