Multi-scale Simulation Study On The Organic Light-emitting Materials And The Living Polymerization In Polymer Systems

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.