【作者】 王艳洁；

【导师】 闫卫东；

【作者基本信息】 河北工业大学 ， 材料学， 2007， 硕士

【摘要】 本论文主要分为两部分:乙烯原位聚合线性低密度聚乙烯(LLDPE)的结构表征和结晶性能研究,并关联了两部分之间的关系。同时,简单考察了支化聚乙烯支链长度对聚合物流变性能的影响。乙烯原位聚合是以乙烯为唯一单体并于同一反应器中,在催化乙烯齐聚形成α-烯烃的同时,“多米诺”催化乙烯与生成的α-烯烃共聚合成线性低密度聚乙烯的方法。目前人们在这方面的研究集中于催化剂及其催化体系的制备以及相应共聚合反应规律的探索。相关聚合方法研究已经取得了可喜突破。由于乙烯齐聚生成的α-烯烃的碳数分布呈Flory分布,与市场上已有的乙烯和单一链长α-烯烃共聚所得支化聚乙烯不同,乙烯原位共聚所得支化聚乙烯在结构上有多种不同长度的支链,且这些支链在主链上的分布情况也不相同。这样的复杂结构必然使其性能有所不同。因此研究乙烯原位聚合产物的结构及性能的关联成为指导催化体系的关键问题。本文通过DSC用SSA方法研究乙烯原位共聚制备的支化聚乙烯链结构的支化非均一性;并同乙烯与特定链长的α-烯烃共聚所得支化聚乙烯的性能相比较。探索简化相对复杂的乙烯原位共聚所得的支化聚乙烯的研究方法,即利用乙烯与特定链长α-烯烃共聚来考察支链长度对聚合物性能的影响规律;利用乙烯与不同含量α-烯烃共聚来考察支链密度对聚合物性能的影响规律。以便为这种新方法在进一步调控所得支化聚乙烯链结构并提高其性能方面提供一定基础。研究发现:1乙烯原位聚合产物与乙烯/长链α-烯烃共聚物的分子链的支化均匀性是十分类似的。经SSA处理,均是以形成晶片厚度较大的为主,晶片厚度较薄的含量很少,但乙烯原位聚合产物各部分含量不均匀,这意味着分子链的支化均匀性较差;而共聚物各部分含量较原位聚合产物均匀。2 XRD结果表明,高聚物的结晶部分呈微晶状态,晶粒尺寸一般在几十纳米左右。乙烯原位聚合产物与共聚物的微晶尺寸十分接近,从而认为有可能利用乙烯分别与不同链长α-烯烃共聚模拟原位聚合产物,以达到简化研究原位聚合产物复杂结构的目的。这对研究乙烯原位聚合产物的结构,从而为进一步研究调控原位共聚制备支化聚乙烯的方法提供研究依据。3等温动力学研究结果表明:乙烯原位聚合产物与共聚产物在结晶方式上趋于一致,其结晶速率常数与成核指数一致。4乙烯/长链α-烯烃共聚物的熔点随加入共单体量的增加呈下降趋势。5根据聚合物结晶度的变化趋势得到支链长度为C-16时,支链参与主链结晶的初步结论。6乙烯/长链α-烯烃共聚物流变研究表明:不同支链长度的几种聚合物粘度随剪切速率的增加变化规律基本一致,近似呈线性规律。在相同的角频率下,支链长度越大,则聚合物的动态粘度越低,其流动性能更加良好。聚合物支链长度大于C-14时,尽管没有达到文献报道的对聚合物流变性能引起变化的长度(C-180),依然会对其流变性能产生影响。更多还原

【Abstract】 This thesis is composed of two parts: (1) structure characteristics of LLDPE via ethylene in-situ copolymerization; (2) investigation on the crystaliizaiton characteristics of LLDPE via ethylene in-situ copolymerization and brief study on the rheology characteristic of ethylene andα-olefin copolymers. Recently, much attention has been paid to LLDPE production via tandem catalysis, involving the use of ethylene as single monomer and two catalysts with different funcions. In this process, one catalyst oligomerizes the ethylene toα-olefin, and the second one is responsible for polymerizing the ethylene and incorporating theα-olefin prepaed in-situ into the growing polymer chain. Many contributions such as the binary catalysts matched and the supported catalysts have been made.α-Olefin from ethylene oligomerization displays Schulz-Flory distribution, i.e. the short chain length is not uniform. As a result, LLDPE via ethylene in-situ copolymerization has various short chain lengths that differ from the ethylene andα-olefin copolymers. Furthermore, the properties may show difference as well. It is worthy of investigating how to forecast even control the chain structure.In this thesis, the macromolecular chain heterogeneity of LLDPE via ethylene in-situ copolymerization was characterized by SSA technique with DSC, which compared to the conventional ethylene copolymers, i.e. ethylnene withα-olefin bearing uniform chain length. It aims to explore how to simplify the complexity of the structure of the ethylene in-situ copolymer to further investigate the relationship between the structure and its properties. We employ the ethylene/α-olefin copolymers to simulate the copolymer via ethylene in-situ copolymerization i.e. use ethylene and the given length 1-alkene copolymers to investigate the effect of short chain length to the polymer properties, simultaneity we utilize ethylene and various comonomer contents copolymers to study the influence of the comonomer content to the polymer performances. As a result, it can lay a foundation for controlling the SCB length and density to obtain a better properties polymer.The main conclusions are as follows:1 The ethylene/α-olefin copolymers and the copolymer via in-situ copolymerization are similar to each other on molecular heterogeneity by SSA which displays multiple melting peaks. The SSA results reveal that the thickest lamellar is in the majority in both the two polymers. But the content of each component doesn’t accord with the uniform distribution in LLDPE via in-situ copolymerization which different from that of conventional ethylene copolymers. It suggests that the heterogeneity of the former is lower than that of the latter.2 Results obtained from XRD show that the crystallites dimensions of various reflections were about decades of nanometers. The ethylene/α-olefin copolymers and the copolymer via in-situ copolymerization were similar to each other on molecular heterogeneity and XRD characters. It reveals that it is possible to use the ethylene/α-olefin copolymers to simulate the copolymer via in-situ copolymerization of ethylene to simplify the complexity of the structure of the ethylene in-situ copolymer.3 Results obtained from isothermal crystallization kinetics show that the crystallization kinetics parameters of the different types LLDPE are similar with each other.4 Melting points of ethylene/α-olefin copolymers decrease with the increasing comonomer content.5 We can conclude that when the length of branch is C-16, the branch can crystalline with the main chain together.6 When the branch length grows up to 14 carbons, the branch has some effect on the rehology characteristics of the polymer.更多还原