【作者】 张昊；

【导师】 王利群； 傅智盛；

【作者基本信息】 浙江大学 ， 高分子化学与物理， 2020， 硕士

【摘要】 在对高端聚乙烯的开发过程中,向聚乙烯链引入功能基团和改变聚乙烯链结构来改变聚乙烯的材料性能是其高性能/高功能化的两种主要途径。(α-二亚胺)镍催化剂不仅能催化乙烯和极性单体的共聚,同时还能通过其“链行走”性能得到带有支链的聚乙烯。本文采用了一系列具有不同骨架结构的(α-二亚胺)镍催化剂(Cat.1～Cat.4),实现了乙烯/甲基丁香酚的共聚,并系统地研究了聚合条件和催化剂结构对共聚行为的影响,针对聚合体系中醚类化合物令聚乙烯支化度降低的现象进行了深入的讨论和研究,得到以下结果:(1)(α-二亚胺)镍催化剂在低温-10℃下对于甲基丁香酚有着更良好的耐受性,能在较高甲基丁香酚浓度下,催化得到较高分子量、较高极性单体插入率的乙烯/甲基丁香酚共聚物。随着聚合温度的升高,聚合活性、分子量和极性单体利用率均下降。(2)(α-二亚胺)镍催化剂的金属中心缺电子性是影响乙烯/甲基丁香酚共聚的关键因素,镍金属中心轴向空间位阻是影响1-己烯/甲基丁香酚共聚的主要因素。Cat.1镍金属中心缺电子性最低,在乙烯/甲基丁香酚共聚中表现出了最高的催化聚合活性和极性单体利用率。Cat.3同时拥有较小的镍中心空间位阻和较低的镍金属中心缺电子性,其催化1-己烯/甲基丁香酚的共聚活性最高,产物分子量也最高。(3)低温下(α-二亚胺)镍催化剂催化乙烯/甲基丁香酚的共聚体系中,存在两种活性中心。一种活性中心活动能力受限,不易发生链行走反应,不易与甲基丁香酚发生反应,生成高分子量、低支化度和低极性单体插入率的聚合物链段;另一种是共聚发生的主要活性中心,产生低分子量、高极性单体插入率的聚合物链,随聚合时间的延长逐渐被甲基丁香酚毒化失活。当体系中甲基丁香酚浓度较高时,两种活性中心均产生支化度低、结晶度高的聚合物链段。(4)向(α-二亚胺)镍催化剂催化乙烯聚合体系中加入二醚类化合物后,聚合产物支化度会降低,且支化度降低程度随二醚类化合物的添加量增大而增大,同时伴随着聚合活性的降低。(α-二亚胺)镍活性中心在链增长时会发生β-H消除反应,具有链转移和链行走两条后续路径,然而二醚的竞争反应让链行走和链增长同时停止,宏观表现就是聚合活性和支化度的同时降低。(5)二醚类化合物相对氯化二乙基铝过量的聚合体系中,利用二醚类化合物可以实现对聚乙烯支化度的调节。二醚类化合物对金属中心的络合能力越强,对支化度和聚合活性的降低幅度越大。二醚类化合物络合能力排序为DME>oDMB>p-DMB。影响络合能力的主要因素是醚的分子结构。聚合体系中,催化剂、助催化剂和二醚类化合物相互影响,要选择合适的[Al]:[Ni]:[diether]摩尔比例才能在保证聚合活性的前提下进行支化度调控。[Al]:[Ni]为200的情况下,[oDMB]:[Ni]不宜超过50,[DME]:[Ni]不宜超过30。当[p-DMB]:[Ni]=360时,[pDMB]:[Al]应当小于0.9。更多还原

【Abstract】 In the development of high performance polyethylene,introducing functional groups into the molecular chain and changing its micro structure are two main methods to change the material properties of polyethylene.α-Diimine nickel catalyst can not only catalyze the copolymerization of ethylene and polar monomers,but also has a peculiar "chain walking" ability,which can be used to prepare branched polyethylene.In this work,a series of α-diimine nickel catalysts(Cat.1～Cat.4)with different framework structures are used to achieve the copolymerization of ethylene / methyl eugenol,and the influence of polymerization conditions and catalyst structure are systematically studied.Furthermore,it is discussed that the behavior of ether compounds to regulate the degree of branching of polyethylene in the polymerization.The following results are obtained:(1)α-Diimine nickel catalyst has better tolerance to methyl eugenol(ME)at low temperature of-10℃,which can prepare polyethylene with higher molecular weight and higher ME incorporation rate at higher methyl eugenol concentration.As the polymerization temperature increases,the polymerization activity,molecular weight,and ME conversion rate all decrease.(2)The electron deficiency of the metal center of the α-diimine nickel catalyst is the key factor affecting the copolymerization of ethylene /ME,while the axial steric hindrance of the nickel metal center is the main reason affecting the copolymerization of 1-hexene/ME.The metal center of Cat.1 has the lowest electron deficiency,showing highest catalytic polymerization activity and ME conversion rate in ethylene/ME copolymerization.Cat.3 has the lower nickel steric hindrance and lower electron deficiency of nickel metal center at the same time,behaving highest catalytic activity for catalyzing the copolymerization of 1-hexene/ME.(3)There are two kinds of active centers in ethylene/ME copolymerization catalyzed by α-diimine nickel catalyst at-10℃.One kind of active center with limited ability to move,which makes it hard to chain walk and react with methyl eugenol,produces polyethylene with high molecular weight,low branching degree and low ME incorporation rate;Another kind of active center where the copolymerization mainly takes place produces polymer chain with low molecular weight and high ME incorporation rate,which is gradually poisoned and inactivated by methyl eugenol with the extension of the polymerization time.When the concentration of methyl eugenol in the system is high,both active centers produce polymer with low branching and high crystallinity.(4)The degree of branching of polyethylene and polymerization activity is decreased after adding diether compounds to polymerization system,and the degree of branching will decrease with diether concentration increasing.During the chain growth process,chain transfer and chain walking start after β-H elimination reaction,which are stopped by the competitive insertion of diether.Therefore,the polymerization activity and the degree of branching are simultaneously reduced.(5)The degree of branching of polyethylene can be regulated by diethers.The stronger the ability of diehers to complex the metal center,the greater the reduction in the degree of branching and polymerization activity.The complexing ability of diethers is DME> o-DMB> p-DMB.The main factor affecting the complexing ability is the molecular structure.In ethylene polymerization,the catalyst,cocatalyst and diethers influence each other,so the appropriate mole ratio of [Al]: [Ni]: [diether] should be selected.When [Al]: [Ni] is 200,[o-DMB]: [Ni] should not exceed 50,[DME]: [Ni]should not exceed 30.When [p-DMB]: [Ni] = 360,[p-DMB]: [Al] should be less than 0.9.更多还原