【作者】 于深；

【导师】 孙平川；

【作者基本信息】 南开大学 ， 高分子化学与物理， 2013， 博士

【摘要】 在最近十几年中,生物启发的仿生分子设计已经成为材料科学研究领域设计、合成高性能高分子材料中引人注目的前沿领域。天然生物材料的独特性能吸引着人们不断对其结构和组成进行深入研究,生物材料的有序性、多级结构、复合特性以及自愈合特性等都已成为先进材料分子设计的仿生模型。最近,受启发于蜘蛛丝的多嵌段交替排列和氢键组装特性,制备高性能多嵌段热塑性聚氨酯倍受关注,并被认为是具有与天然高性能生物材料竞争的潜能。本文通过新的仿生分子设计来调控聚氨酯体系的多级结构,制备出集多种优良性能于一体的系列聚氨酯新材料,具体包括：1.受蜘蛛丝的多级结构,生物体的自愈合现象和生物弹性体对交联的精密控制的启发,我们通过新的分子设计合成了一种高力学性能、可回收、再加工同时具有白愈合性能的新型交联聚氨酯材料。在这种新材料的设计合成中,通过聚氨酯硬段中带有的马来酰亚胺悬垂侧基和多官能度呋喃交联剂之间的Diels-Alder (DA)反应,将可逆共价交联键可控地设计在聚氨酯硬段的氢键密集区域；通过在交联剂分子结构中引入氨酯键来防止它的加入破坏原有氢键作用所形成的聚氨酯微相分离结构,同时提高硬段的氢键密度以增强力学强度。上述分子设计就形成了包含柔性相和刚性相的微相分离,密集的氢键组装和可逆共价DA键组成的具有多级结构的新型聚合物材料。这种材料不仅具有优良的力学性能,还具备交联聚合物特有的耐溶剂性和耐热性,以及可再生利用和自愈合等综合特性。另外,通过简单调节交联剂的加入量就可以实现对材料力学性能在较宽范围内的连续调节。这项工作为合成与制备高性能聚合物材料提供了一个新的途径。2.有机-无机杂化与结晶结构的存在是天然生物材料具有优异力学性质的重要机制,基于这些分子机理我们使用超声分散快速成型的共混方法制备了热塑性聚氨酯弹性体/纳米二氧化硅的复合材料,采用多种实验技术研究了球状纳米二氧化硅对聚氨酯弹性体结晶行为的影响。TEM表明纳米二氧化硅在聚氨酯弹性体中有很好的分散性。DSC实验发现高温退火后等温结晶处理的聚氨酯纳米复合材料中软段结晶性和玻璃化转变温度显著提高,纳米二氧化硅的加入量影响玻璃化转变温度和结晶熔融焓最终的平衡值以及它们的增长速率。固体NMR实验发现退火后复合材料中的软段分子链运动受到了限制,而硬段的链运动明显提高。上述实验结果说明硬段分子链间氢键在高温下被破坏,在退火过程中硬段与纳米二氧化硅作用使得硬段链运动增强,进而促进了与硬段相连的软段的结晶能力提高。基于以上研究结果,我们建立了聚氨酯纳米复合材料在高温退火过程中微观结构和动力学演化的物理模型。另外,通过溶剂交换法制备了热塑性聚氨酯弹性体/锂藻土纳米复合材料,发现了类似的软段诱导结晶行为。3.热塑性聚氨酯弹性体中具有软硬交替的多嵌段高分子链形成的微相分离结构,它是这类材料拥有优异性能的结构基础。通常使用DSC来研究聚氨酯在温度变化时的玻璃化转变和结晶相变过程,但这种方法难以同时提供在温度变化中分子水平的结构演化信息。我们使用红外热分析方法对热塑性聚氨酯弹性体进行了包括升温和降温的连续变温过程中的红外分析。通过van’t Hoff方程处理不同温度下的红外吸收峰强度得到聚氨酯中每个官能团在连续变温过程中的表观焓变值,从而得出每个官能团在变温过程中的热力学信息,进而获得比DSC实验更丰富的微观结构演化信息。更多还原

【Abstract】 In the last decades, bio-inspired or biomimetic molecular design and synthesis of high-performance and self-healing polymeric materials have become a paradigm and a fascinating area of research. Natural biomaterials with excellent combination properties attract more and more research on biomimetic materials preparing. Recently, inspired by the multiblock copolymeric and H-bonding assembly nature in spider silks, the preparation of high-performance segmented thermoplastic polyurethanes has received substantial attention due to the potential in rivaling the advanced material in nature. In this dissertation, both new molecular design and organic-inorganic hybrid are utilized to form hierarchical structures in polyurethane elastomers with high performance.1. Nature finds its intriguing strategy to make high-performance and degradable biomaterials. Inspired by hierarchical structures in spider silk, delicately controlled cross-linking in elastin and self-healing in organism, a new molecular design is proposed to prepare advanced polymeric materials with integrated excellent properties including high mechanical strength and toughness, good solvent and heat resistance, self-repairing ability and eco-friendship into one structure. Incorporation of reversible covalent cross-links among H-bonding hard segments in linear segmented polyurethane via DA reaction between maleimide pendant groups of the chain extender (N-(2,3-dihydroxyethyl) maleimide) on hard segments and furan cross-linker (1,6-hexamethylene-bis(2-furanylmethylcarbamate)), thus thermal reversibility related to recyclability and self-healing ability can be accomplished by the retro-DA (RDA) reaction. The cross-linker containing urethane bonds is specially selected to promote the miscibility in H-bonding hard domains and further increase the H-bonding density in polymer matrix, and thus to enhance the mechanical properties. Therefore, a hierarchical structure is formed organically by microphase separation, densely H-bonding assemblies and reversible covalent cross-linking. The synthesized polymers not only exhibit excellent comprehensive mechanical properties, including high stiffness, strength, and toughness, but also have good solvent and heat resistance, and can be well reshaped and re-mended at an elevated temperature, making it eco-friendly and have great potential for widely industrial applications.2. Polyurethane/silica nanocomposites are prepared by solution mixing procedure, and the effect of nano-silica on the crystalline behavior in these nanocomposites is investigated by various techniques. TEM result indicates that nano-silica is well dispersed in polyurethane matrix. It is found from the DSC experiments that the crystallization of soft segments are obviously enhanced after annealing at high temperature and subsequent isothermal crystallization at10℃, the addition of nano-silica affects the final glass transition temperature and the crystallinality of soft segments, as well as the rate of increment. Solid-state NMR reveals that the mobility of soft segments are restricted after annealing, while the mobility of hard segments obviously enhanced. The above results reveal that the interchain hydrogen bonding among hard segments are broken at high temperature, and increased interaction of hard segments and nano-silica results in the high mobility of hard segments, thus promotes the crystalline ability of the soft segments connected with hard segments. On the basis of the above results, a model concerning the evolution of the structure and dynamics in polyurethane nanocomposites under high-temperature annealing is proposed. In addition, polyurethane/Laponite nanocomposites are prepared by solution exchange method, and a similar result of Laponite induced crystallization in soft segmnets are observed.3. Phase transitions of polyurethane are investigated by differential scanning calorimeter (DSC) and Fourier transform infrared (FTIR) spectroscopy. FTIR spectra of the sample are measured as a function of temperature both in heating and cooling processes. The intensities of bands at different temperatures are dealt with the van’t Hoff equation to get results as apparent enthalpy change of every single chemical group in the polyurethane to continuously various temperatures, which can provide detailed thermodynamics information besides the results from DSC.更多还原