【作者】 张文；

【导师】 谢兴益； 熊成东；

【作者基本信息】 四川大学 ， 材料工程（专业学位）， 2023， 博士

【摘要】 聚乙烯亚胺（PEI）是一种含有（C₂H₅N）_n重复单元的多胺化合物,同时具有高分子和小分子胺的化学特性,这种独特的化学结构使之具有诸多优良特点,例如较高的反应活性、强阳离子特性和吸附性等,并在造纸印刷、CO₂减排、污水处理、非生物基因运载等领域展现出良好的应用前景。不同于小分子胺结构简单和改性困难的特点,PEI结构中的部分胺基可与其它的官能团反应进行接枝改性,从而优化PEI的物理化学性质,拓宽其应用范围。然而,实现PEI规模化应用的前提条件是原料来源可靠、成本低廉,这就要求PEI的制备工艺简单、质量可控。目前,PEI主要由氮丙啶单体在酸催化下聚合而成,而氮丙啶单体具有高毒性、易挥发、不稳定的缺点,使之无法长距离储存和运输,且该合成路线工艺复杂、涉及强酸强碱,且会产生大量副产物盐。因此,亟待设计一种非氮丙啶的PEI合成工艺以解决上述问题。与小分子胺类似,PEI的多胺结构能可逆吸收CO₂,这使之在CO₂减排方面有较大应用潜力。本课题组研究发现PEI的CO₂加合物（PEI-CO₂）在代替传统聚氨酯发泡剂方面具有一定的应用价值,但因成本太高,暂未能实现大规模生产。此外,虽有研究表明改性后的PEI-CO₂可用于聚氨酯发泡,但吸收CO₂后形成的加合物为粉末状,分子极性大,难溶于白料组分。为了改善该类发泡剂与白料的相容性,在发泡过程中需要添加一些小分子（如阻燃剂）作为稀释剂,而这些小分子物质的引入可能会产生泡沫收缩、压缩强度不够等问题。因此,希望找到一种不加或少加稀释剂就能具有良好相容性的PEI-CO₂类型发泡剂。针对上述两个方面的问题,本文首先重新设计了PEI的合成路线,探究出了一种非氮丙啶路线合成PEI。其次,为了降低发泡剂的生产成本,采用价格低廉的五乙烯六胺为原料,经扩链法合成了含亚苯基聚乙烯亚胺类似物（PEIP）,经过接枝改性、吸CO₂工艺制备了PEIP-CO₂类型发泡剂,并将该类发泡剂用于生物基多元醇、聚酯多元醇、聚醚多元醇发泡体系验证其发泡效果。论文具体研究内容如下:（1）设计并制备了复合金属催化剂NiCuFeO_x和NiCuCoO_x,用于乙醇胺的催化聚合反应。研究表明在反应温度为170℃、反应时间为48 h、不加溶剂条件下所制备的产物具有最大聚合度。核磁共振和质谱技术表征结果表明两种催化剂所得产物的谱图相似,且核磁碳谱数据未发现支化PEI特有的8种碳信号,而存在较多的哌嗪环结构。质谱结果表明原料发生了聚合反应,但聚合度不高,重复单元为5左右。因此,以乙醇胺为原料的催化聚合反应并未获得理想的目标产物。（2）考虑到羟基与胺基的N-烷基化反应活性不高,可能需要更严苛的反应条件（如升高温度、延长反应时间、更换催化剂等）才能达到预期效果,因此将反应原料调整为反应活性较强的2-卤乙胺（以盐的形式存在,2-氯乙胺盐酸盐或2-溴乙胺氢溴酸盐）。研究表明2-卤乙胺在氢氧化钠溶液中可以一锅法合成PEI,且该过程不用分离氮丙啶中间体。通过对合成PEI的分子量、结构、产率等综合分析,结果表明最合适的原料为2-氯乙胺盐酸盐,且相对较优的合成过程可分为不同温度下的两个阶段。第I阶段,在25℃下反应24 h,2-氯乙胺发生分子内和分子间脱氯化氢的反应,分别转化为氮丙啶（主要产物,产率77.5%）和PEI低聚物;第II阶段,在100℃下水热反应24 h,该阶段氮丙啶分子可以被PEI低聚物上的胺基开环,促使链生长,直到耗尽氮丙啶单体。此外,氮丙啶分子本身也可以发生开环聚合,形成具有氮丙啶环端基的PEI链,而一个端基氮丙啶环可以被同一PEI链上的一个仲胺基攻击,形成末端哌嗪环或更大的环,并终止链的生长。反应过程中产生的副产物乙醇胺和哌嗪能以末端羟乙基、醚键或链内哌嗪环的形式结合到最终PEI链中,但所有的这些杂链节以及末端哌嗪环只占最终聚合物总碳的4%。本章对氮丙啶在碱性条件下的聚合机理进行了深入研究,该项工作对指导设计更安全、更经济的PEI聚合物合成路线具有较大意义。同时,将该方法用于聚丙烯亚胺（PPI）的合成也可以得到目标聚合产物,表明该路线有一定的普适性。（3）基于对上述一锅法合成PEI反应机理深入理解的基础上,设计了以2-氯乙胺盐酸盐为原料,将其所含的总氮量作为基准,加入一定比例的小分子有机胺（丁胺、己胺、辛胺）,从而在聚合反应中一步合成烷基接枝的PEI(yC_{x N}-PEI,y为接枝率,x为碳链长度)。使yC_{x N}-PEI吸收CO₂至饱和可得到发泡剂yC_{x N}-PEI-CO₂,并将其用于生物基多元醇聚氨酯发泡,测试结果表明此方法所得的发泡剂具有良好的发泡效果。由前面的研究可知,小分子胺的掺入不利于高分子量PEIs的形成,但试验表明,这并不影响发泡性能。由于所述的小分子有机胺极性小,在极性溶剂水中的溶解度不大,致使加入的小分子胺不能全部接枝到PEI主链上（实际接枝率一般低于投料量）,这将造成原料的浪费,但在实际工业化生产过程中可以进行回收处理。（4）为解决PEI-CO₂发泡剂生产成本高、与多元醇（聚氨酯原料）相容性差的问题,采用五乙烯六胺（PEHA）与对苯二甲醛（TPA）缩合,并化学还原形成的希夫碱键,探索了一种经济合成PEI-CO₂类聚合物（PEIP）的方法。通过对原料投料比的设计,制备了四种不同分子量的PEIP（1.8k、3.6k、9.1k、17.8k）,并将它们均接枝10%的辛基缩水甘油醚（C₈）,然后吸收CO₂制成发泡剂,用于蓖麻油衍生多元醇Polycin^?M365聚氨酯的发泡研究。通过对粘度、相容性、泡沫形貌、泡沫密度等数据分析可知:分子量为3.6k时（即3.6k PEIP）的发泡效果最佳。随之,以3.6k PEIP为原料,通过考察侧链链长、接枝率对发泡剂发泡性能的影响,发现10%C₈-3.6k PEIP-CO₂具有最优发泡性能。将此发泡剂与普通PEI（M_n=2500）制备的10%C₈-PEI-CO₂进行对比实验,发现当发泡剂在多元醇Polycin M365中的固含量为2%时,10%C₈-3.6k PEIP-CO₂可以完全溶解,而10%C₈-PEI-CO₂则含有不溶性小颗粒,说明前者与多元醇的相容性更好。此外,对比两种发泡剂的CO₂宏观释放速率,发现10%C₈-3.6k PEIP-CO₂的释放速度更快。结果表明,PEIP-CO₂类发泡剂的发泡效率高于PEI-CO₂类发泡剂。为了降低泡沫密度,将发泡剂的量增至白料的质量浓度约20%,并调整其他助剂的含量,最终可得到密度和力学性能均满足要求的泡沫产品。此外,为了拓宽PEIP基发泡剂的应用范围,将制备的发泡剂用于聚酯体系,却发现了不一样的结果,即当配方中存在较多乙二醇和丙三醇时,接枝率低或碳链更短的发泡剂具有更优异的发泡性能,且10%C₄-PEIP-CO₂在聚酯聚氨酯中的综合性能最佳。尽管生物基多元醇更绿色环保,但因聚醚多元醇具有来源可靠及结构可变的优点,仍然是目前聚氨酯生产中应用最广的多元醇。因此,以聚醚4110多元醇体系为研究对象,采用与聚醚4110结构相似的二丙二醇单甲醚缩水甘油醚（PPG）接枝3.6k PEIP,合成了PPG接枝率为5%、10%、15%的发泡剂,并与3.6k PEIP-CO₂（相当于接枝率为0）、10%PPG-PEI-CO₂进行对比研究。显微镜和动态光散射测试结果表明PEIP类发泡剂的侧链接枝率越高,其在聚醚4110中相容性越好;PEI-CO₂发泡剂和PEIP-CO₂发泡剂在接枝率相同情况下,后者的相容性和发泡性能更好。综合分析,10%PPG-3.6k PEIP-CO₂在聚醚4110中的发泡效果最佳。在该发泡剂的配方设计中并未使用稀释剂,最终也能取得良好的发泡效果。更多还原

【Abstract】 Polyethyleneimines（PEIs）possess a polyamine structure with a repeating unit of（C₂H₅N）_n,which has chemical properties of polymers and low molecular weight amines.This unique chemical structure gives PEIs many excellent features such as high reactivity,strong cationic properties and adsorption,leading to applications in the fields of paper printing,CO₂ emission reduction,wastewater treatment,non-viral gene carriers,etc.Unlike low molecular weight amines,which have simple structures and difficult to be modified,the amine groups in PEIs can react with other functional groups,thereby optimizing the physicochemical properties of PEIs and broadening their application fields.However,the prerequisite for the large-scale application of PEIs depends on a reliable source and low cost,which requires a simple and quality-controlled preparation of PEIs.Currently,PEIs are mainly produced by acid-catalyzed polymerization of aziridine which has disadvantages of high toxicity,volatility,and instability,making it impossible to be stored and transported over long distances.Moreover,the synthesis route of aziridine is complicated involving strong acids and bases,with massive wastes of salt byproducts.Therefore,there is an urgent need to design a non-aziridine synthesis of PEIs.Similar to low molecular weight amines,PEIs can reversibly absorb CO₂;this is a promising application for CO₂ emission reduction.Our research group has found that CO₂ adducts of PEIs（PEI-CO₂）have potential application value in replacing traditional polyurethane blowing agents,but the cost is too high to realize large-scale production currently.In addition,although some studies have shown that the modified PEI-CO₂ can be used for polyurethane foaming,the adducts formed are powder with high polarity,and they are difficult to dissolve in the white components.To improve the compatibility between the blowing agents and the white components,some low molecular weight compounds（such as flame retardants）need to be added as diluents in the foaming mixture,and the introduction of these small molecule substances may lead to problems of foam shrinkage and insufficient compression strength.Therefore,it is desired to find a PEI-CO₂ type blowing agent that has good compatibility with the white components without or with less diluent addition.To address the above two aspects,this paper first redesigned the synthesis route of PEIs,explore a non-aziridine route synthesis of PEIs.Second,in order to reduce the production cost of foaming agent,using cheap pentaethylenehexamine as raw material,the chain extension method was used to synthesize the phenylene-containing polyethylenimine-like polymers（PEIPs）,and the PEIP-CO₂ type blowing agents was prepared by grafting modification and CO₂ absorption process.Finally,the foaming effect of PEIP-CO₂ blowing agents in bio-based polyol,polyester polyol,and polyether polyol foaming systems was studied.The details of the study in this paper are as follows.（1）Composite metal catalysts NiCuFeO_x and NiCuCoO_x were designed and prepared for the catalytic polymerization of ethanolamine.The results showed that the maximum degree of polymerization was obtained when the reaction temperature was170℃,the reaction time was 48 h and the solvent was free.The NMR and mass spectrometry techniques showed similar spectra of the products obtained from the two catalysts,and the ¹³C NMR spectra did not show the featured eight carbon signals of typical branched PEIs,with many piperazine ring structures instead.The mass spectrometry results indicated that polymerization of the raw material occurred,but the degree of polymerization was not high,with a repeating unit of about 5.Therefore,the catalytic polymerization of ethanolamine did not obtain acceptable target product.（2）Considering that the N-alkylation reaction between alcohols and amines is not highly active,harsh reaction conditions（such as high temperature,long reaction time,more active catalysts）may be required to achieve the desired effect.Therefore,the raw material was changed to the more active 2-haloethylamine（2-chloroethylamine hydrochloride or 2-bromoethylamine hydrobromide）.It has been shown that PEIs can be synthesized in a one-pot process from 2-haloethylamine in aqueous Na OH solution,without separation of the aziridine intermediate.Through the comprehensive analyses of the molecular weight,structure and yield of synthesized PEIs,the results show that the most suitable raw material is 2-chloroethylamine hydrochloride,and the relatively optimal synthesis involves a two-stage process at different temperatures.Stage I at 25℃ for 24 h is sufficient to transform 2-chloroethylamine into aziridine（major product,yield 77.5%）and PEI oligomer,via intramolecular and intermolecular dehydrochlorination,respectively.Stage II involves hydrothermal reaction at 100℃ for 24 h,where the aziridine molecules can be ring-opened by amino groups from the PEI oligomer to maintain chain growth until the depletion of aziridine monomer.Meanwhile,aziridine molecules themselves can undergo ring-opening polymerization forming aziridine-ring-terminated PEI chains.A terminal aziridine ring can be attacked by a secondary amino group in the same PEI chain,forming a terminal piperazine or larger ring,and terminating chain growth.Two side products,ethanolamine and piperazine,can be incorporated into the final PEI chains as terminal hydroxyethyl groups,ether linkages,or in-chain piperazine rings.All these chain impurities,together with the terminal piperazine rings,account for as few as 4%of the total carbons in the final polymers.This study provides an insight into the mechanisms of aziridine polymerization in basic conditions,leading to the design of safer and more economical synthesis of PEIs polymers.Also,the application of this method to synthesize poly（propyleneimine）s（PPIs）is successful,indicating that this synthesis has some general applicability.（3）Based on the in-depth understanding of the reaction mechanism of the above one-pot synthesis of PEIs,2-chloroethylamine hydrochloride was designed to be used as raw material,the total nitrogen content in it was taken as the benchmark,and a certain proportion of small molecular organic amines（butylamine,hexamine,octylamine）were added,so as to one pot synthesize alkyl-grafted PEIs(yC_{x N}-PEIs,where y is the grafting ratio and x is the carbon chain length).The blowing agent yC_{x N}-PEI-CO₂s can be obtained by making yC_{x N}-PEI absorb CO₂ to saturation,which can be used for foaming of bio-based polyol polyurethane.The test results show that the blowing agent obtained by this method has good foaming effect.According to the previous study,the incorporation of small molecular amines did not favor the formation of high molecular weight PEIs,but tests showed that this did not affect the foaming performance.Due to the weak polarity of these small molecular organic amine,their solubility in polar solvent water is not large,resulting in small molecular amines cannot be completely grafted to PEI backbones（the actual grafting rate is generally lower than the theoretical values）,this will cause a waste of raw materials.However,the unreacted raw materials can be recycled during a real industrial manufacture process.（4）To address the problems of high production cost of PEI-CO₂ blowing agents and poor compatibility with polyols（polyurethane raw materials）,an economical synthesis of PEI-like polymers（PEIPs）was explored via condensation between pentaethylenehexamine（PEHA）and terephthalaldehyde（TPA）,followed by chemical reduction of the as-formed Schiff base linkages.Four PEIP with different molecular weights（1.8k,3.6k,9.1k,17.8k）were prepared by the design of raw material feeding ratio,and all of them were grafted with 10%ethylhexyl glycidyl ether（C₈）and then absorbed CO₂ to make blowing agents for the foaming of polyurethanes from Castor oil derived polyols Polycin^?M365.The analyses of data such as viscosity,compatibility,SEM,and foam density showed that the best foaming performance was achieved at a PEIP molecular weight of 3.6k（3.6k PEIP）.Subsequently,by exploring the effects of side chain length and grafting rate on the foaming performance of the blowing agents based on 3.6k PEIP,it was found that 10%C₈-3.6k PEIP-CO₂ had the optimal foaming performance.A comparison experiment was conducted between this blowing agent and 10%C₈-PEI-CO₂,and it was found that 10%C₈-3.6k PEIP-CO₂could be completely dissolved when the solid content of the blowing agent in the polyol Polycin M365 was 2%,while 10%C₈-PEI-CO₂ contained insoluble small particles,indicating that the 10%C₈-3.6k PEIP-CO₂ was more compatible with the polyol.Furthermore,comparing the CO₂ releasing rates of the two blowing agents,it was found that the release rate of 10%C₈-3.6k PEIP-CO₂ was faster.As a result,PEIP-CO₂ based blowing agents exhibited higher foaming efficiency than the PEI-CO₂analogue.To reduce the foam density,the solid content of blowing agent was increased to about 20 wt.%of the white components,resulting in foams with density and mechanical properties that meet practical applications.In addition,to broaden the application of PEIP-CO₂ blowing agents,the as-prepared blowing agents were used in polyester systems,but different results were found.In other words,the blowing agents with lower grafting rates or shorter side chains had superior foaming performance in cases of the presence of ethylene glycol and glycerol in the formulations.Overall,10%C₄-PEIP-CO₂ exhibited the best performance in polyester systems.Although bio-based polyols are more sustainable,polyether polyols are still the most popular polyols in polyurethane foams because of their reliable source and variable molecular structures.Therefore,polyether 4110 polyol system was used to study the blowing performance.The 3.6k PEIP was grafted with methyl dipropylene glycol glycidyl ether（PPG）which is structurally similar to polyether 4110,with the PPG grafting rates of 5%,10%,and 15%.The resultant CO₂ adducts were compared to 3.6k PEIP-CO₂（i.e.,a grafting rate of 0）and 10%PPG-PEI-CO₂ in foaming performance.The microscopic images and dynamic light scattering tests showed that the higher the alkyl grafting rate of PEIP-CO₂ blowing agents,the better their compatibility in polyether 4110.When PEI-CO₂ blowing agents and PEIP-CO₂blowing agents have the same grafting rate,the latter have better compatibility and foaming performance.Overall,10%PPG-3.6k PEIP-CO₂ in polyether 4110 gave the best foaming performance.Our investigation proved that without diluents used in the formulations,a good foaming performance could be achieved as well.更多还原