【作者】 刘玉华；

【导师】 吕中元；

【作者基本信息】 吉林大学 ， 物理化学， 2010， 博士

【摘要】 有机电致发光材料应用于通讯、信息、显示等许多领域,是当前国际上的一个研究热点。有机电致发光器件具有低压直流驱动、高亮度、高效率、制作工艺简单及易实现全色大面积显示等优点,从而引起了人们对该类器件开发与设计的极大兴趣。理论研究为理解发光材料的微观发光机制提供了理论分析和支持,对实验合成新的发光材料和开发发光材料的潜在应用价值具有重要的指导意义。自由基聚合(free radical polymerization, FRP)是指含有碳碳双键的单体通过自由基链式加成反应形成聚合物的反应。FRP已经成为合成功能性高分子很重要的一个途径。链长和化学组分分布对于共聚物的性质来讲是非常重要的,例如它们可以决定材料的物理和力学性质。因此运用理论模拟方法计算聚合反应速率常数并研究聚合速率、单体浓度、自由基分布、以及扩散速率等因素对自由基聚合过程和聚合产物的影响,引起人们越来越多的关注。表面引发聚合反应作为一种新兴的合成工艺,在材料表面的修饰与改性中发挥着越来越重要的作用。研究聚合反应速率和转化几率等因素对高密度下聚合物刷性质的影响非常有实际意义。可逆的活化反应中的原子转移自由基聚合反应(atom transfer radcial polymerization, ATRP),由于它的特殊优势,已经成为一种非常有力的合成技术。在理想的ATRP反应中,聚合反应速率应保持一个合理的值以确保反应效率,同时活化速率和去活化速率常数也应很大,这样才能更好地控制反应。体系中可控活性自由基的浓度取决于活化/去活化进程的平衡,因此,设计具有更多活性的新的催化体系是很有挑战性的工作。然而由于缺乏有效的技术,人们很少研究去活化过程的影响,而在可控自由基聚合反应中控制分子量的分布在很大程度上取决于去活化过程。上述体系涉及包括电子的不同空间、时间尺度上的行为,因此单一尺度模拟方法无法对这类材料的电子及结构信息进行整体的合理描述。多尺度计算机模拟方法可以更明确地给出这些物理现象的微观本质,从而帮助从本质上对这些规律进行理解和认识。本论文结合量子力学(quantum mechanics QM)、分子动力学(molecular dynamics, MD)和粗粒化分子动力学(coarse-grained molecular dynamics, CGMD)模拟方法,从不同尺度上对以上课题进行了细致研究。这些方法不但能直观地给出体系的静态图像,而且可以详尽地描述体系的动态行为,现在已经被广泛应用到材料学、化学、物理学、生物学等领域中。本论文结合QM、MD、CGMD方法并提出多尺度模拟模型,对以上课题进行了细致研究。主要内容包括:(1)利用密度泛函方法(density funetional methods, DFT)研究1,1’,2,3,4,5-六苯基硅杂环戊二烯(HPS)晶体的电子结构和电荷传输性质。利用MD结合DFT研究温度和压力的变化对HPS晶体的力学性能的影响。MD模拟结果表明,适当增加压力和温度有利于增加HPS晶体的电荷传输。通过能带机理和跳跃机理的分析,我们发现HPS晶体的空穴传输性质优于电子传输性质。因而得出以下结论:①空穴传输优于电子传输;②适当增加压力和温度都有利于获得更好的电荷传输性质。(2)结合量子化学和传统过渡态理论(transition state theory, TST)计算了乙烯和丙烯自由基聚合反应的速率常数。所有的电子结构在B3PW91/3-21G水平上进行了优化计算,稳定的单点能和最小能量路径(minimum energy path, MEP)上的附加点和传统过渡态理论的反应速率常数都是在MPW1PW91/6-311G(d,p)水平进行单点能校正。利用速率常数定义了聚合反应几率(Pijl),构造了乙烯丙烯共聚反应的粗粒化动力学模拟模型,并利用该模型研究了不同引发剂组成比例的乙烯丙烯共聚反应。聚合反应的数均分子量和链长分布都显示此模型能够反映真实的实验结果。我们发现反应速率常数和链端自由基周围的单体浓度都影响链上组分的序列分布。(3)利用粗粒化分子动力学方法研究了高密度表面引发聚合反应过程中,不同聚合速率和不同转化几率对产物聚合物刷性质的影响。鉴于活化/去活化过程非常重要,因此我们提出了一个表面引发聚合反应(surface initiated polymerization, SIP)模型,其中明确包含活化/去活化可逆过程。我们发现在SIP反应中生成的聚合物刷主要取决于聚合反应几率与活化/去活化动态过程。为了在相对短的时间内得到高密度引发下的低多分散性指数(polydispersity index, PDI)聚合物刷,可调节聚合反应几率和活化/去活化过程发生的比率。相对快或者相对慢的链增长过程都可以得到有较低PDI值和较高接枝密度的聚合物刷,但要采取不同的活化程度:对于较慢的链增长可以选择较快的活化反应;对于较快的链增长,活化反应需控制得足够慢才能得到理想的聚合物刷。更多还原

【Abstract】 In the past decades, organic electroluminescent materials have become a fascinating field for their diverse potential applications in communication, information, and flat-panel displays. There has been great interest in investigating organic electroluminescent materials and devices. Theorical studies can help us to understand the microscpic electroluminescent mechanism and to design novel light-emitting materials by exploring their structure-property relations.Free-radical polymerization (FRP) is a typical technology by which a polymer chain is formed from the successive addition of free radical blocks. Now FRP is a key synthesis route for obtaining a wide variety of different polymers and material composites. People are more and more interested in theoretical calculating the rate constants of polymerization reaction and studing the free radical polymerization processes and the polymer properties which are influenced by polymerization rate, monomer concentration, free radical distribution, and diffusion, and so on.As a kind of newly developed technology, surface-initiated polymerization plays a critical role in the field of surface grafting for the materials. In living radical polymerizations, the atom transfer radcial polymerization (ATRP) has emerged typically as one of the most powerful synthetic techniques in polymer sciences for its unique advantages. In the ideal ATRP, the polymerization rate is kept at a reasonable value, meanwhile both the activation and deactivation rate constants should be kept large to provide good control of polymerization. The radical concentration is predominantly determined by the equilibrium of the activation/deactivation processes. Thus, the exploitation of novel catalytic systems that are very active and efficient should be an encouraging work. However, for lack of effcient techniques, deactivation processes had been much less studied. As control over molecular weight distribution in ATRP is limited by the rate of deactivation, fully taking into account of deactivation process becomes especially important.The above systems include different space and time scales of electrons, so the simulation technique at a single scale can not describe the structural and electronic information of these materials. Multi-scale simulations can finely deliver the details of the physical processes. They can help us to understand and explore the laws in these natural phenomena clearly. According to different research objects, we combine quantum mechanics (QM), molecular dynamics (MD) and coarse-grained molecular dynamics (CGMD) simulations to study the topics mentioned above in detail. The main results are as follows:(1) The structural, electronic, and charge transport properties of 1,1’,2,3,4,5-hexaphenysilole (HPS) crystal are investigated using density functional theory (DFT). The influences of the temperature and pressure variations on the mechanical as well as the charge transport properties of HPS crystal are studied by MD simulations combining with DFT calculations. By the analysis of the hopping mechanism and the band-like mechanism, we find that the hole may move slightly easier than the electron for the HPS crystal. Thus we can conclude that (i) the mobility of the hole is larger than that of the electron; and (ii) moderately higher pressure and temperature are in favor of better charge transport properties.(2) A combined quantum chemistry and transition state theory (TST) rate constant calculation scheme is performed on different radical reactions involving ethylene and propylene to estimate the rate constants. The electronic structure information is obtained at the B3PW91/3-21G level, and the single-point energies of the stationary points, extra points along the minimum energy path (MEP) and the theoretical rate constants are calculated at the MPW1PW91/6-311G(d,p) level. We can define normalized polymerization probabilities (Pijl) by theoretical rate constants, and we propose a CGMD simulation model to study the copolymerization between ethylene and propylene. The copolymerization with different percentage of initiator has been investigated using our model. The results of the variation of number-averaged molecular weight during polymerization and the chain length distribution after polymerization show that our model can closely simulate the polymerization process of real experiment. We find that the rate constants and the number of monomers around the chain radical ends strongly influence the chain length distribution and the segment distribution along the chain backbone.(3) The surface initiated polymerizations (SIP) with different polymerization rate and different ratio of the transformation (activation/deactivation) probability under high grafting density are investigated using CGMD simulations. Regarding the significance of the activation/deactivation process, we present a model of SIP by taking into consideration of the activation/deactivation process explicity. We find that polymerization rate and the ratio of activation/deactivation process greatly determine the properties of polymer brushes in SIP reactions. By modifying the polymerization rate and tuning activation/deactivation process, we can obtain the polymer brushes with low polydispersity index (PDI) in relatively short time. For obtaining the surface initiated film in relatively short time and simultaneously with low PDI and high graft density, we can choose relatively fast or slow chain propagation process. For slow chain propagation, it is better to choose fast activation process, and for fast chain propagation, the activation should be controlled slower so that the properties of the brushes are acceptable.更多还原