【作者】 王睿；

【导师】 朱世平； 罗英武；

【作者基本信息】 浙江大学 ， 化学工程， 2008， 硕士

【摘要】 梯度共聚物是指共聚单体组成沿大分子链长呈一定梯度分布的聚合物,从广义上讲,嵌段共聚物和无规共聚物是梯度共聚物的特例。由于链段组成的梯度变化,梯度共聚物具有独特的温度、力学响应以及界面性能,在阻尼材料和共混物相相容剂上有很大的应用潜力。本文的工作主要是回答两个问题:(1)梯度共聚物如何制备,如何精确控制其组成分布;(2)梯度共聚物有怎样的性能,不同的组成分布对其性能有怎样的影响。本文第一部分工作是针对一些活性自由基聚合动力学方面的基本问题进行研究,这是合成梯度共聚物的基础。首先建立了可逆加成-断裂链转移(RAFT)均聚合过程在分隔体系——细乳液聚合体系中的动力学模型。通过理论推导和实验结果的比较,分析了RAFT细乳液聚合出现缓聚现象的原因。并通过分隔体系的构筑,对RAFT聚合机理进行辨识,同时给出了准确测量RAFT平衡常数的方法。然后,对RAFT共聚合过程做了理论描述,给出了表观平衡常数的表达式,并讨论其对共聚合速率的影响。接着,将上述共聚合模型推广到RAFT交联过程中,给出了凝胶点的判据和凝胶转化率的解析表达,考察了分子内交联反应对凝胶转化率的影响,并研究了支化分子支链数的分布。在充分理解活性自由基聚合动力学的基础上,本文第二部分工作是将化学工程中的反应器技术引入到活性自由基聚合过程中,来实现梯度共聚物的合成。通过分别对ATRP和RAFT共聚合过程的模拟,讨论了利用程序化单体滴加的半连续操作来控制共聚物组成分布的可行性。设定的共聚物结构包括组成均一的、线性的、双曲线形的梯度共聚物以及含梯度部分的多嵌段聚合物等多种形式。本部分还对半连续反应过程中的一些动力学问题进行了考察和解析分析。本文第三部分工作应用高分子统计力学的知识对梯度共聚物/均聚物三元共混体系的相行为进行了研究。首先利用de Gennes提出的无规相近似(Random PhaseApproxiamtion)研究了共混体系的临界现象,确定了Lifshitz点的位置及其物理属性与链梯度结构间的关系;其次利用自恰场理论(Self-consistent FieldTheory)计算了不同梯度共聚物共混体系的相图,讨论了共聚物层状结构溶涨均聚物链的能力以及共聚物在均聚物中的溶解度等指标随梯度共聚物组成分布的变化;最后对共混体系出现的微相结构进行了考察,计算了均聚物和共聚物在微相中的密度分布,研究了梯度共聚物的界面特性。通过对梯度共聚物链结构的设计,共聚物的界面结构、微相形态以及其它性能都将得到优化。更多还原

【Abstract】 The gradient copolymer is a special kind of copolymer that the composition chain gradually along the chain backbone. Owing to its gradient compositon profile, this kind of copolymer has distinct response to the thermal and mechnical stimulation as well as special interfacial properties. As the result, gradient copolymer has great potential to be damping material and compatibilizer in immicible polymer blends. This thesis focus on questions in two aspects: one is how could the gradient copolymer with various composition profiles be prepared, the other is how these different composition gredients affect properties of the polymer.The first part of the thesis discussed some fundamental aspects in living radical polymerization, based on which the gradient copolymer is synthesized. At first, a mathematical model is developed to describe the kinetics of reversible addition-fragmentaion chain transfer (RAFT) in miniemulsion polymerization. Through comparing the theoretical results with experimental data, we discussed the reason for the retardation in RAFT miniemulsion polymerization. By making the advantage of the spatial compartmentalized system, we discriminated the mechanism of RAFT polymerization and provided a method to accurately measure the RAFT equilibrium constant. In addition, the apparent RAFT equilibrium constant in copolymerization process is expressed, and related to the copolymerization rate. Then, the copolymerization model is applied to describe the RAFT crosslinking process. Both the criteria of the gel point and analytical expression for gel conversion were provided. The effect of intramolecular crosslinking on gelation process was investigated and the branching distribution in hyperbranched polymers was also calculated.Based on the comprehension of living radical polymerization kinetics, we combined the methodology of chemical engineering, that is the reactor policy, with living radical polymerization techniques to synthesize the gradient copolymer in the second part of this thesis. Through modeling both RAFT and ATRP process, the feasibility of using semi-batch operation with programmed monomer feeding to control the composition profile in gradient copolymer was theoretically proved. The targeted products involved uniform, linear gradient, hyperbolic gradient Copolymers and block Copolymers with gradient segments. We also discussed some kinetic problems appearing in semi-batch process and try explaining them in analytical way.In the last part of the thesis, some theories in polymer physics were employed to investigate the phase behaviors in ternary gradient copolymer/homopolymer blends. First, the random phase approximation suggested by de Gennes was used to study the critical phenomenon. The effect of chain gradient on the position and physical nature of Lifshitz Point was dicussed. Sequentially, self-consistent field theory was employed to calculate the phase diagrams of the blends. The poisiton of different phase region were located. In addition, the relation between chain gradients and swelling ability of copolymer layer as well as the dissolvability of copolymer chains in homopolymer phase were also investigated. Finally, we analyze the mesophase structure of the blends. The density profiles of both copolymer and homopolymer were calculated, and the interfical properties of different gradient copolymer were also studied. We suggested that, by designing the composition profile of gradient Copolymers, the interfacial structure as well as the morphology and property of the whole blend will be fine-tuned.更多还原