【作者】 何勇；

【导师】 常杰； James Runt；

【作者基本信息】 华南理工大学 ， 能源环境材料及技术， 2013， 博士

【摘要】 聚氨酯由异氰酸酯和醇组分通过逐步聚合制备而成，广泛应用在泡沫、弹性体、涂料、胶黏剂、纤维和生物材料等领域。聚氨酯的分子主链由软段和硬段交替连接而成。含有较低玻璃化转变温度（T_g）的软段组成连续的基质，赋予材料低温柔顺性；而含有较高T_g或者熔点（Tm）的硬段通过物理交联形成微区，这些微区在低T_g的软段基质中起到了增强填料的作用，提高材料的性能，如机械性能、热性能以及耐溶剂性。聚氨酯的优异性能与其化学结构和加工条件形成的微相形态结构有关。阐明结构和形态之间的关系对于开发和应用这些材料有重要的意义。采用非等量的甲苯二异氰酸酯（TDI）与三官能团的三羟甲基丙烷（TMP）反应制备聚氨酯预聚物，通过凝胶渗透色谱仪（GPC）对化学反应过程进行跟踪。研究表明TMP的位阻效应是影响分子量分布的最主要因素，特别是影响分子量较高的区域。最优化的NCO/OH比值为3.0，反应温度为50℃。通过GPC分析归属了TDI、TMP-TDI、TMP-2TDI、TMP-3TDI、2TMP-5TDI以及3TMP-7TDI组分。采用电喷雾质谱（ESI-MS）对GPC的归属进行确认。此外，一些其他的副产物，如脲和脲基甲酸酯在ESI-MS和核磁氢谱（1H NMR）中能够识别。脲基甲酸酯的含量随反应温度的升高而增多。结果表明TDI-TMP型聚氨酯预聚物的定量分析不仅能够避免或者减少副反应的发生，而且能够为薄膜蒸发器的设计以及控制分离过程提供基本数据。对TDI-TMP型聚氨酯预聚物在不同温度下的反应动力学进行研究。通过反滴定法和高效液相色谱（HPLC）分别测定异氰酸酯的浓度和TDI异构体的含量，实现对整个聚合反应过程进行跟踪。该聚合过程采用逐步滴加进料的方法，化学反应能够很好地符合二级反应动力学模型。采用三种工业常见的TDI混合物，其2,4-TDI和2,6-TDI含量的比值分别为65:35、80:20和100:0。通过研究反应温度、初始化学计量比和TDI异构体对残余2,4-TDI和2,6-TDI含量的影响，建立残余TDI异构体单体和溶剂的稳定回收模型，不同批次间制备的聚氨酯预聚物化学结构重复性好。该模型已经应用到工厂进行连续化生产具有可控化学结构组成的聚氨酯预聚物。以三种具有不同对称性和平面结构的二异氰酸酯单体为原料，采用溶液聚合的方法制备聚脲，选用的二异氰酸酯单体包括2,6-TDI、2,4-TDI和4,4’–二苯基甲烷二异氰酸酯（MDI），讨论异氰酸酯结构的对称性对相分离形态、氢键行为和分子动力学的影响。结果表明，对称的异氰酸酯结构有利于硬段通过双配位氢键自组装形成线条状的硬段微区。微相分离的硬段微区在聚合物中起到物理交联点的作用，进而影响分子动力学。采用小角X光散射（SAXS）定量微相分离的程度。通过宽频介电松弛谱（DRS），以聚合物的动力学为分子探针，研究微相分离的微区的存在和变化过程。SAXS结果表明微相分离的程度随异氰酸酯结构对称性的增加而增加。尽管差示扫描量热仪（DSC）没有发现2,6-TDI和2,4-TDI型聚脲的软段T_g有明显差别，但是DRS结果表明当异氰酸酯的对称性从2,6-TDI降低到2,4-TDI，由于软相基质内存在更多硬段的混合，软段的移动性降低。由于脲内存在强的双配位氢键，共聚物的Maxwell-Wagner-Sillars （MWS）界面极化过程的介电强度能够稳定维持在220℃的高温。采用傅里叶红外光谱（FTIR）研究2,6-TDI、2,4-TDI和MDI型聚脲的变温氢键行为。结果表明在170℃以上脲链节开始分解，两个与缩二脲有关的新峰在1727cm^-1和1678cm^-1出现。在较低的退火温度150℃下不存在任何副反应，TDI型聚脲在加热和冷却过程中具有相同的氢键行为，有序脲羰基的含量随温度的升高而降低，无序和自由的脲羰基含量逐渐增加。然而，在异氰酸酯结构不共平面的MDI型聚脲中，可能由于在溶液浇注制模过程中得到的是“淬火”的形态，退火处理明显有利于有序脲羰基的增多，这也与原子力显微镜（AFM）观测到的硬段棒状微区长度和宽度逐渐增大相符合。结合广角X射线衍射（WAXD）和SAXS的发现，结果显示微结构与退火温度联系密切。DSC分析表明随退火温度的增加，软段T_g的温度逐渐减小，表明微相分离的程度在增强。更多还原

【Abstract】 Polyurethanes, formed by the step growth polymerization of isocyanates and polyols, proveto be a highly versatile class of materials having applications such as foams, elastomers, coatings,adhesives, fibers and biomaterials. Polyurethanes are composed of soft segments and hardsegments arranged alternately. The soft segments with a low glass transition temperature （T_g）form the continuous matrix, which exhibits low temperature flexibility. The hard segments withhigh T_gor melting points （Tm） tend to self-assemble into domains through physical crosslink.These domains mostly act as reinforcing filler in the low T_gcontinuous matrix and improve theproperties of the material, such as mechanical, thermal performances and solvent resistance. Theexcellent performances of polyurethane are generally attributed to their morphology structure ofthe materials formed by their special chemical structure and processing conditions. Understandingthe structure-property relationship is crucial in the development and application of thesematerials.Polyurethane prepolymer prepared from nonequivalent amounts of toluene diisocyanate（TDI） over trifunctional trimethylolpropane （TMP） was followed by gel permeationchromatography （GPC）. Steric hindrance of TMP is considered as the main factor affecting themolar mass distribution, especially in the higher molecular weight region. An optimum reactioncondition is the initial NCO/OH ratio of3.0and the reaction temperature of50℃. Thenpolyurethane prepolymer could be purified through the thin film evaporator with excellentproperties. The components, such as TDI, TMP-TDI, TMP-2TDI, TMP-3TDI,2TMP-5TDI and3TMP-7TDI, are observed in GPC analyses, and the results are further verified by electrosprayionization mass spectrometry （ESI-MS）. Additionally, other side products such as urea andallophanate are presented in ESI-MS and1H NMR analyses. The formation of allophanates ishighly dependent on reaction temperature. These results indicate that the quantitative analyses forthe TDI-TMP based polyurethane prepolymer do not only favor to avoid or reduce the sidereactions, but also supply fundamental data for designing thin film evaporator and controlling theseparating process.Reaction kinetics of TDI-TMP polyurethane prepolymer at various temperatures is studied. The progress of the polymerization reaction was monitored by measuring the concentration ofisocyanate groups and TDI isomers by means of back-titration and High Performance LiquidChromatography （HPLC）, respectively. The kinetics of dropwise addition method, compared withthe conventional one-shot method, is well described by a second order equation. This procedure isoptimized by comparing the deviations between experimental data and theoretically calculateddata. The effects of temperature, initial stoichiometry and TDI isomers on the amount of excess2,4-TDI and2,6-TDI were investigated. Three commercially available TDI mixtures, that is,65:35,80:20and100:0ratio of2,4-TDI/2,6-TDI respectively were used. A recycling model ofunreacted TDI isomers and solvent is established to reach a stable process and yield polyurethaneprepolymer with good reproducibility. This model has been applied in the chemical plant toprepare polyurethane prepolymer with precisely defined chemical compositions in a continuousprocess.Three diisocyanates with different symmetry and planarity,2,6-TDI,2,4-TDI and4,4’-diphenylmethane diisocyanate （MDI）, were used to synthesize polyureas in solution. Theeffects of diisocyanate symmetry on the phase separated morphology, hydrogen bonding behaviorand molecular dynamics are studied. The symmetrical diisocyanate structure allows excellentself-assemble of hard segments into ribbon like domains by strong bidentate hydrogen bonding.The strongly microphase separated domains in these polymers act as physical crosslinks, and they areexpected to strongly influence molecular dynamics. Small-angle X-ray scattering （SAXS） was utilizedto quantify microphase separation characteristics, and broadband dielectric relaxation spectroscopy（DRS） revealed the sensitivity of polymer dynamics to the presence and changes in microphaseseparated domains in the polymers. SAXS results indicate that the degree of microphase separationis enhanced by the symmetric diisocyanate structure. DRS results show that the soft segmentmobility is significantly reduced due to the hard segment mixing into soft matrix when thesymmetry of the diisocyanate is decreased from2,6-TDI to2,4-TDI, although no pronounceddifference of soft segments T_gis detected in differential scanning calorimeter （DSC）. Thedielectric strength of Maxwell-Wagner-Sillars （MWS） interfacial polarization process in allcopolymers displays a temperature independent plateau extending well over220℃because of the presence of strong bidentate hydrogen bonding between urea containing segments.The temperature dependence of hydrogen bonding for polyureas based on2,6-TDI and2,4-TDI and MDI has been studied by Fourier transform infrared spectroscopy（FTIR）. Theresults show that urea linkages decompose above170℃, and two new peaks at1727cm^-1and1678cm^-1associated with the formation of biuret are evident. At a lower annealing temperature at150℃without side reactions, TDI based polyureas exhibit reversible behavior for hydrogenbonds during heating and cooling processes. The intensity of ordered urea carbonyls decreaseswith temperature while the intensity of the free and disordered urea carbonyls increase gradually.However, in MDI based polyureas with noncoplanar diisocyanate structure, thermal annealingcauses the rise of the ordered urea carbonyls due to the “quenched” morphology formed bysolution casting, consistent with the increased length and width of ribbon like hard domainsobserved in AFM. In combination with the findings from Wide-angle X-ray diffraction （WAXD）and SAXS, the results suggest that the microstructure is also highly dependent on the annealingtemperature. DSC analysis demonstrates that the soft segment T_gdecreases with increasingannealing temperature, indicating a higher degree of microphase separation morphology formed.更多还原