【作者】 蔡浩鹏；

【导师】 熊传溪； 王钧；

【作者基本信息】 武汉理工大学 ， 材料学， 2007， 博士

【摘要】 环氧树脂是航天、航空及国防领域最常用的热固性聚合物，该类树脂具有优异的热稳定性、电绝缘性能和物理、机械性能，但其固化物质脆、不耐冲击和容易应力开裂。为了提高环氧树脂的韧性，一个成功的方法是在环氧树脂或固化剂主链中引入柔性链段。这种方法虽然能有效提高环氧树脂的韧性，但环氧树脂固化物的玻璃化转变温度、强度和模量也随之大幅度下降，改性后的聚合物材料只适合作为胶粘剂等非结构材料使用，无法用作高性能结构复合材料的基体。本文首次提出在环氧树脂链上接枝长的一端“自由”的柔性聚醚侧链分枝提高环氧树脂韧性的改性思路，达到提高环氧树脂韧性而不降低树脂固化物的强度和模量的目的。系统地研究了聚醚柔性侧链环氧树脂的合成、固化物结构和性能的关系，分析了柔性侧链的网络结构，揭示了柔性侧链环氧树脂的增韧机理，为环氧树脂的增韧改性提供了一种新的方法。首先以1:1二乙二醇单丁醚（Mw=162）、甲苯2，4-二异氰酸酯（TDI）和双酚A型环氧树脂为原料，利用TDI邻对位-NCO反应活性的差异和双酚A型环氧树脂中羟基的反应活性，控制反应条件合成了具有二乙二醇单丁醚侧链的环氧树脂。采用傅立叶变换红外光谱（FTIR）、测定环氧值的变化等方法对合成的侧链环氧树脂进行结构表征，证实合成过程中环氧树脂的羟基发生了反应，而环氧基团没有变化。并通过改变二乙二醇单丁醚为不同分子量（Mw=450，1200，2000）的聚乙二醇单甲醚（mPEG）合成了含有不同侧链长度的环氧树脂。为了确定侧链环氧树脂的固化工艺参数，采用非等温DSC法研究了环氧树脂／甲基四氢邻苯二甲酸酐（MeTHPA）固化反应机理。研究表明，侧链的引入及含量对环氧树脂的固化反应机理没有影响，和纯环氧树脂一样，按n级固化反应模型进行，反应级数n在0.9～1之间。根据固化动力学参数，确定二乙二醇单丁醚侧链环氧树脂／MeTHPA固化体系的最佳工艺条件为：在100℃固化2小时凝胶后升温到120℃恒温固化2小时，最后升温到160℃后固化6小时。同理研究不同分子量的mPEG侧链环氧树脂固化反应动力学参数表明侧链长度对环氧树脂的固化机理也没有影响，其反应级数同样在0.9～1之间。热失重分析（TG）表明，温度高于220℃时，接枝在环氧树脂侧链上的氨基甲酸酯键才会发生分解，故环氧树脂固化过程中侧链不会分解。利用合成的柔性侧链环氧树脂研究了树脂固化物的机械性能。结果表明，引入柔性侧链环氧树脂的韧性得到明显提高。侧链的质量百分含量在10％～15％之间时韧性达到最大，同时固化物的强度和模量不变。纯环氧树脂固化物的冲击韧性和断裂韧度分别为17.92 kJ·m^-2和2.34 MN·m^-3/2，是典型的脆性断裂。对于二乙二醇单丁醚侧链环氧树脂，当侧链的质量百分含量为10％时达到最大值，冲击韧性和断裂韧度分别比纯环氧树脂提高了34.1％和84.6％。柔性侧链环氧树脂在低温下的增韧效果更加明显，ITPE的含量为10％时，在-50℃时冲击韧性大小为18.72kJ·m^-2，而此时纯环氧树脂的冲击韧性仅为7.55kJ·m^-2。动态热机械分析（DMA）表明固化物存在两个介质损耗峰，而扫描电镜（SEM）分析表明固化物断面没有孔洞和两相分离。这说明侧链环氧树脂和没有侧链环氧树脂由于分子量的差异，造成分子链交联网络的不均匀性，在亚微观上形成两相结构。增韧的机理是一端“自由”的柔性侧链穿插在环氧树脂主链的交链网络中，在材料受到冲击能量的时候，可以起到应力分散和承受应力的作用，固化体系韧性增加。通过对断裂能G_IC建立数学模型分析得出，韧性的增加和侧链的质量百分含量成线性关系。同时分析侧链长度和韧性之间的关系表明侧链对环氧树脂韧性的影响不仅和侧链的数量有关，还和侧链链节单元有关。相同链段的侧链对树脂性能的改变主要和侧链相同链节（-CH₂-CH₂-O-）的数量有关，而侧链长度影响较小。更多还原

【Abstract】 Epoxy resin （EP） for its outstanding advantages on high thermal stability,excellent electric properties and technique as advanced resin matrix has been widelyused in high science and technique fields, such as aviation, sPaceflight and nationaldefence, etc. However, epoxy resin is generally rather bittle, because of its highlycrosslinked structure. Improving the toughness of this resin is very important forepoxy technology, a successful attempt is flexible crosslinking agent toughening orflexible crosslinking in main-chain of epoxy. However, the presence of flexiblechain may decrease the thermal stability, the strength and the modulus of thematerial. Whilst for adhesive applications such decreases in modulus andtemperature resistance are usually of no significance, in matrices forfiber-composites such effects can lead to unacceptable decreases in the properties ofthe firer-composite. In this thesis, the new approach to improve the toughness is tosynthesize EP with long polyether side chains, where the side chains don’t undergophase-seParation on curing the blends. The synthetic technique, structure andproperties of EP with side chains, curing mechanism and structure and properties ofepoxy blends are studied. The toughening micromechanisms responsible for themarked increases in toughness arising from the presence of flexible side chain arethen identified.First, using toluene diisocyanate （TDI） as a coupling agent between the epoxyand hydroxyl-terminated polyethers forming a urethane linkage with the former andthe latter respectively, the EP with long polyethers side chains are synthesized.Polyethers used is diethylene glycol monoethyl ether （Mw=162）. The progress of thereaction and the structural changes during modification process are studied using IRspectroscopy （FTIR）, differential scanning calorimetry （DSC）, viscosity data, andchemical analysis （epoxy value determination）. The studies support the propositionthat TDI acts as a coupling agent between the epoxy and diethylene glycolmonoethyl ether forming a urethane linkage with the former and the latter. Usingmono methoxy polyethylene glycol （mPEG） of different molecular weight （Mw=450, 1200, 2000）, EP with different length side chain are synthesized.The curing mechanism and kinetics of epoxy with polyether side chains reactedwith Me THPA are studied by non-isothermal differential scanning calorimetry（DSC）. The curing reaction is proceeding in nth cure mechanism, the same as thepure epoxy. The order of curing reaction is 0.9～1, gained with kinetics calculation.Besides, the content of side chains don’t affect in the cure mechanism.The activationenergy （Ea） and reaction frequency factor of the system are increased and reactionrate was decreased by the addition of flexible polyether side chains into the epoxyresin. Based on the kinetics results, the optimization of cure processing is discussed:100℃for 2h, 120℃for 2h and 160℃for 6h. DSC shows that the chain lengthdoesn’t affect in the cure mechanism. The order of curing reaction is 0.9～1 also,gained with kinetics calculation. The urethane linkage will be decompounded underhigh temperature. The TGA data show that the thermal degradation temperature is220℃. The urethane linkage can’t be decompounded on curing the blend for thetemperature of curing EP blends.The mechanical properties of epoxy modified with flexible sidechain arestudied. The mechanical properties of the cured blends show that the toughness ofepoxy modified with flexible side chain is increasing markedly. At that time, theway of flexible side chain toughening epoxy can retain the modulus of the curedepoxy resin. The pure epoxy polymer is very brittle with imPact toughness and thefracture toughness (K_IC) values of about 17.92 KJ·m^-2 and 2.34MN·m^-3/2, with istypical of a brittle thermosetting epoxy polymer. The addition of flexible side chaingives an immediate increase in toughness. There is a steady increase in toughnesswith increasing content of ITPE, and a maxium value of imPact toughness=24.03KJ·m^-2 and K_IC=4.32 MN·m^-3/2 is obtained at 10wt% ITPE, the measured toughnessstarts to decrease somewhat. On the other hand, the flexural strength and the flexuralmodulus of the cured epoxy resin retain invariable. The toughness of epoxymodified with flexible side chain is increasing more markedly under lowtemperature. The imPact toughness of epoxy with modified with 10wt% ITPE is18.72 KJ·m^-2 under -50℃. At that time, the imPact toughness of the pure epoxy isonly 7.55 KJ·m^-2。Dynamic mechanical thermal analysis （DMA） show that ITPE/ER blends clearly display two maxima on the tanδvs T curves. However, scanning electronmicroscopy （SEM） of the fracture surfaces shows that polyethers side chain doesn’tundergo phase-seParation upon curing the blends and there are not cavities inblends.The different Mw of epoxy and modified-epoxy leads to thermodynamicdifference during curing the blends. So, the network of the curing blends isasymmetric. It is the toughening mechanism for the flexible side chain modifiedepoxy. Besides, the polyethers chains were wrapped in the three-dimensionalnetwork of the epoxy. The imPact energy could be held back or delayed due to theexistence of the flexible chain. In this case, the dissiPation （or absorption） ofrelatively large Part of the imPact energy may be attributed to crack bifurcation andcrack Path alternation. The modeling analysis of the fracture energy (G_IC) shows thatthe toughness is linear increasing with the amount of side chain in the EP when theside chain is invariable.The maxium value of imPact toughness and flexural strengthare all obtained at 10～15wt%, making no difference with length side chain. Theresult show that the effect of side chain to epoxy resin lies on the amount of uniformchain node （-CH₂-CH₂-O-）, but has nothing to do with the length of the side chain.更多还原