【作者】 胡进；

【导师】 张心亚；

【作者基本信息】 华南理工大学 ， 化学工程， 2021， 博士

【摘要】 受生物体组织可以自发修复损伤的启发,自修复材料通过引入动态可逆的相互作用,包括可逆共价键和非共价键作用力,可以在外界刺激作用下自发地修复损伤,增加材料的安全性、稳定性和使用寿命。然而,目前大多数自修复材料由于可逆弱键的引入,普遍存在着力学性能较差的缺点,严重限制了其实际应用。聚氨酯材料通过控制软硬段的形态和比例,其力学性能广泛可调,通过将可逆作用力引入聚氨酯体系,预期可以解决自修复材料力学强度和自修复性能难以兼顾的关键性问题。论文针对上述问题,以构建具有高力学强度的自修复聚氨酯弹性体材料为目标,基于不同的自修复体系,通过悬挂链四重氢键超分子交联、调控硬段含量、动态共价交联、可逆复合扩链等不同的方法,在保证优异自修复性能的前提下增强材料的力学强度。主要的研究内容如下:（1）为了提高基于可逆弱键（二硫键）扩链的自修复聚氨酯的力学强度,在使用二硫代二乙二醇（SS-diol）扩链的基础上,同时用UPy-diol扩链引入悬挂链UPy（2-脲基-4-嘧啶酮）基团,形成四重氢键超分子交联进行增强,得到无色透明的自修复聚氨酯弹性体。弹性体的拉伸强度随UPy含量的提高而先增加后减小,UPy-diol比例在20-30%之间最佳,拉伸强度最高可提升到改性前两倍达到25 MPa,同时断裂伸长率和韧性分别为1460%和101 MJ m^-3。与此同时,材料的自修复性能没有随UPy含量的上升而明显下降,结合TGA、DMA和流变学的表征,说明悬挂链的设计保证了UPy四重氢键在升温断开后,游离侧基的存在可以促进分子链的扩散运动,使得材料的粘流转变温度和松弛时间只是略有增加,更高UPy含量的样品也可以表现出相近的自修复性能。因而,强度最高的PU-U2S8样品也显示出优秀的自修复性能,表面划痕在100°C时30 min后可完全消失,同时切断的样品拼回后在100°C加热2 h可达到90%以上的修复率。（2）以对苯二甲醛和乙醇胺为原料合成含有动态亚胺键的二醇扩链剂Imine-diol,通过改变HMDI（二环己基甲烷二异氰酸酯）与其的预聚比调控硬段含量,优化制备了透明的高强度自修复聚氨酯弹性体PUI。力学性能的研究表明,在60 wt%的临界比例前,硬段含量越高,弹性体强度越高,超过60 wt%后,材料表现为塑性,且强度随硬段含量的增加而减小。自修复性能研究表明,硬段含量的增加会使得材料的有效修复温度提高,自修复能力下降。性能最优的PUI-3样品的拉伸强度最高可达41 MPa,断裂伸长率和韧性分别为836%和166 MJ m^-3,同时具备高效的自修复性能,宽达50μm的划痕在70°C时只需5 min就基本修复,切断的样品在80°C修复2 h就可以达到95%以上的修复率。将Imine-diol扩链剂中的具有平面刚性的C=N键,换成柔性的C-S键进行对比研究后发现,C=N键扩链的样品力学性能明显更强,说明亚胺C=N键的物理结构刚性和化学动态可逆性兼具的特点,是PUI样品可以同时具备高力学强度和优秀自修复性能的原因。（3）以四溴双酚A（TBBPA）为可逆扩链剂,没食子酸丙酯（PG）为动态交联剂,通过优化控制交联密度和硬段含量,制备一种基于可逆酚氨基甲酸酯的无色透明高强度自修复聚氨酯弹性体PPU。原料配比由设计的交联密度和硬段含量一起唯一确定,以此分别独立研究交联密度和硬段含量对力学性能和自修复性能的影响。经过优化后,交联密度为0.5 mmol cm^-3且硬段含量为60 wt%的PPU-0.5-60弹性体样品的拉伸强度最高可达46 MPa,断裂伸长率和韧性分别为615%和89 MJ m^-3,同时具备优异的自修复能力,可以在100°C经过2 h的修复几乎完全恢复其力学强度,达到95%的修复率。此外,分别用几乎不可逆的双酚A（BPA）和三羟基丙烷（TMP）单独代替扩链剂或交联剂,作为控制对比样品,比较结果说明TBBPA和PG的共同组合是才是材料同时具备高力学强度和较高自修复性能的原因,其中含有苯环的PG作为刚性交联剂对提高材料力学强度有着关键作用。（4）首先合成含有Diels-Alder（DA）可逆加成物的二醇扩链剂DA-diol,然后将DA-diol与1,4-丁二醇（BDO）进行复合扩链,通过调节两种扩链剂的比例,制备一种高力学强度的透明自修复聚氨酯弹性体材料DAPU。其中BDO扩链剂保证了材料室温时的力学强度,DA-diol扩链剂赋予了材料升温后的自修复性能。综合调控DA-diol在复合扩链剂中的比例,利用DA可逆反应平衡对温度的高敏感性,只需较低的扩链比（0.2-0.3）,引入少量DA可逆加成物,就可以在不影响BDO扩链聚氨酯的力学强度的同时,使材料具备高效的自修复性能。最优的DAPU-0.2弹性体具有65 MPa的超高拉伸强度,其断裂伸长率和断裂韧性分别为1050%和216 MJ m^-3,同时弹性体在110°C修复2 h后就可以达到95%以上的修复率。更多还原

【Abstract】 Inspired by the fact that biological tissues can spontaneously repair their mechanical damages,self-healing materials with the introduction of dynamic covalent bonds and non-covalent interactions can repair the damages under external stimuli,which can improve the safety,stability,and service time of materials.However,due to the incorporation of weak bonds,most self-healing materials suffer from the poor mechanical performances,which severely limits their industrial application in the real world.By controlling the morphology and ratio of hard and soft segments,the mechanical properties of polyurethane can be widely adjustable.Thus,by introducing reversible interactions into the chain segments of polyurethane,it has a great possibility to solve the key problem of how to balance the mechanical strength and self-healing performance.In order to solve the above problem,the purpose of this thesis is to fabricate a self-healing polyurethane elastomer with high mechanical strength.Based on different self-healing systems,taking the strategies of supramolecular crosslinking with dangling quadruple hydrogen bonds,adjusting hard segment contents,dynamic covalent crosslinking and mixed chain extension with reversible bond,the mechanical strength was greatly improved without sacrificing the self-healing efficiency.The main research contents are as follows.（1）For improving the mechanical strength of self-healing polyurethane with weak dynamic bonds（disulfide bond）,on the basis of chain extending with 2-hydroxyl disulfide（SS-diol）,dangling UPy（2-ureido-4[1H]-pyrimidinone）group was introduced by additional chain extending with UPy-diol.UPy group can form complimentary quadruple hydrogen bonds as supramolecular crosslinking to strengthen the obtained colorless transparent self-healing polyurethane elastomer.The tensile strength of the elastomer increases first and then decreases with the increasing of UPy content.The optimal ratio of UPy-diol is between 20-30%,and in this range,the tensile strength can be increased twice as before modification,reaching 25 MPa.The elongation at break and toughness are 1460%and 101 MJ m^-3,respectively.At the same time,the self-healing ability did not significantly decrease with the increase of UPy content.Combining the characterization of TGA、DMA and rheology test,it is convinced that this design ensures the existence of dangling side chain which can promote the chain diffusion after UPy quadruple bonds being broken at elevated temperatures,so that the flow transition temperature and relaxation time of the material are only slightly increased.Therefore,samples with increased UPy content can display similar self-healing performances.PU-U2S8 sample with the best mechanical properties also shows excellent self-healing performance.The surface scratches completely disappeared after 30 minutes at 100°C,and the cut sample can be healed at 100°C for 2 h with a healing efficiency of more than 90%.（2）Imine-diol,a diol chain extender with dynamic imine bonds was synthesized from terephthaladehyde and ethanolamine.By changing the prepolymerization ratio of HMDI/Imine-diol,the hard segment contents were regulated to prepare an optimized transparent high-strength self-healing polyurethane elastomer PUI.Mechanical tests show that the tensile strength was improved with the increase of hard segment content,when below the critical ratio of 60 wt%.After exceeding this critical content,the polyurethane will display plastic-like mechanical behavior and the mechanical strength will be reduced with continuing increased hard segment content.Self-healing tests show that an increase of the hard segment content will constantly increase the effective healing temperature and lower the self-healing ability.The best-performing PUI-3 sample has a tensile strength up to 41 MPa,with elongation at break and toughness are 836%and 166 MJ m^-3,respectively.Meanwhile,it exhibited excellent self-healing performances.Surface scratches with a width up to 50μm completely diminished in 5mins at 80°C.The cut sample can be fully repaired at 80°C with a healing efficiency of 95%.By comparing the planar rigid C=N double bond in Imine-diol chain extender with the rotable C-S single bond of its counterpart chain extender,it is found that the sample with C=N bond was much stronger.The results indicate that the coexistence of structural rigidity and highly dynamic reversibility in C=N bond is the main reason why PUI elastomers can simultaneously have high mechanical strength and excellent self-healing ability.（3）Using tetrabromobisphenol A（TBBPA）as reversible chain extender and propyl gallate（PG）as dynamic crosslinker,a transparent robust self-healing polyurethane elastomer（PPU）based on reversible phenolic carbamate was successfully prepared,through optimizing the crosslink density and hard segment content.The feed ratios of raw materials were uniquely determined by the specified crosslinking density and hard segment content.Based on this,the independent effects of crosslinking density and hard segment content on mechanical properties and self-healing abilities were studied separately.After optimization,the best performing sample PPU-0.5-60 elastomer has a tensile strength up to 46 MPa,and its elongation at break and toughness are 615%and 89 MJ m^-3,respectively.Meanwhile,it has excellent self-healing ability.The mechanical strength of cut sample can be recovered after 2 hours of healing at100°C,reaching a healing efficiency of 95%.In addition,the nearly irreversible bisphenol A（BPA）and trihydroxylmethylpropane（TMP）were chosen to replace as chain extender or crosslinker separately to prepare control samples.The comparison results indicate that the combination of TBBPA and PG is responsible for the remarkable mechanical properties and excellent self-healing performances of PPU elastomers.And the crosslinker PG with structure rigidity plays a key role in improve the mechanical strength.（4）The reversible chain extender DA-diol with reversible DA adducts was synthesized and was combined with 1,4-butanediol（BDO）as complexed chain extender.By adjusting the ratio of the two chain extenders,a transparent self-healing polyurethane elastomer DAPU with high mechanical strength was prepared.BDO chain extended hard segments ensures the high strength at room temperature,while the DA-diol endows it with self-healing ability at elevated temperatures.Taking advantage of the high temperature sensitivity of DA reaction equilibrium,only a small amount of DA adducts,resulting from a low DA-diol chain extending ratio（0.2-0.3）,will make the DAPU elastomer highly self-healable without sacrificing its mechanical strength.The optimal DAPU-0.2 sample has an ultra-high tensile strength of 65 MPa,and its elongation at break and toughness are 1050%and 216 MJ m^-3,respectively.Meanwhile,the elastomer can be fully healed at 110°C for 2 h,achieving a healing efficiency of 95%.更多还原