The Synthesis Of PPE Alloys In Water And The Simulation Of Their Molecular Dynamics

Poly(2,6-dimethyl-1,4-phenylene ether) (PPE) also known as poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) is a widely used engineering thermoplastic and has been applied in various fields due to its excellent electrical and mechanical properties. However, the high glass transition temperature (Tg=210℃), high melt viscosity and low oxidative stability of PPE make it difficult to process. On the other hand, the glass transition temperature of PPE is inadequate for solder resistance and PPE is soluble in organic solvents such as aromatics and chlorinated aliphatics. The problems mentioned above could be solved by blending PPE with other polymers or modifying PPE chains chemically. In addition, the preparation of PPE in organic solution in industry is harmful to environment. Thus, synthesizing modified PPE and its alloys in water is necessary for both experimental and theoretical reasons.This dissertation mainly focused on the synthesis of PPE containing double bonds on its side chains and PPE alloys in aqueous solution. Furthermore, the molecular simulation was used to study the molecular dynamics of different PPE blends on both atomistic and coarse-grained scales. The main work and results are as follows.Poly (2-allyl-6-methyl-1,4-phenylene-co-2,6-dimethyl-1,4-phenylene ether)s (allyl-PPEs) were synthesized through oxidative coupling copolymerization of 2,6-dimethylphenol and 2-allyl-6-methylphenol in water. The copper(II)/ethylene diamine tetraacetic acid (Cu(Ⅱ)/EDTA) complex catalyzed copolymerization was conducted in alkaline aqueous solution in oxygen atmosphere. And low-molecular-weight allyl-PPEs with relatively narrow molecular weight distributions were obtained. FTIR,1H and 13C NMR spectroscopies were employed to identify the structure of allyl-PPOs. Crosslinking reactions of allyl-PPEs were carried out under UV treatment with the presence of photo initiator. It is environmentally benign to synthesize allyl-PPE in aqueous solution. The residual copper ions in the product obtained in water medium were much lower than that in the product synthesized in organic solvent. The dielectric constant and dissipation factor of the product produced in this way were very low.A one-pot synthetic approach for the preparation of poly(2,6-dimethyl-1,4-phenylene ether)/polystyrene (PPE/PS) alloy in aqueous medium was developed. The method was based on the combination of the oxidative coupling polymerization of 2,6-dimethylphenol (DMP) to form PPE in the presence of reactive swelling agent, styrene (St), and in situ reverse atom transfer radical polymerization (RATRP) of St initiated by 2,2’-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (AIBI) in alkaline aqueous solution. The complex of CuCl2 and 4-dimethylaminopyridine (DMAP) was utilized as the catalyst to catalyze the two types of polymerization mentioned above. Oxygen was employed as the sole oxidant to synthesize PPE. The introduction of St during the oxidative polymerization of DMP could increase the molecular weight of PPE. Finally thermodynamically compatible PPE/PS alloy was successfully prepared.An environmentally friendly one-pot synthetic method to prepare thermodynamically partially compatible poly(2,6-dimethyl-1,4-phenylene ether)/polymethylmethacrylate (PPE/PMMA) alloy in water was developed based on green chemistry. Methylmethacrylate (MMA) was added into the mixture before the end of the polymerization of 2,6-dimethylphenol (DMP) in alkaline aqueous solution. MMA could penetrate into PPE particles and then in situ reverse atom transfer radical polymerization (RATRP) of MMA was initiated by 2,2’-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (AIBI) after the oxidative polymerization. The polymerization of DMP and MMA were both catalyzed by the complex consists of CuCl2 and 4-dimethylaminopyridine (DMAP). Finally thermodynamically partially compatible PPE/PMMA alloy was successfully prepared. The obtained product possessed a cellular structure with PPE embedded in PMMA.Detailed atomistic molecular dynamics simulations were performed to investigate the behavior of two different binary blends, a miscible system poly(2,6-dimethyl-1,4-phenylene ether)/polystyrene (PPE/PS) and a immiscible system poly(2,6-dimethyl-1,4-phenylene ether)/poly(methyl methacrylate) (PPE/PMMA). We compared these two blends to study how PPE behaves when blended with different polymers. In both cases, the structure and phase behavior of polymer melts were studied by means of radial distribution functions (RDFs). Radii of gyration illustrate the static properties. Packing features of the benzene rings were observed in PPE and PS, both PS and PPE were well dispersed over the whole time scale of simulation. Furthermore, there was a tendency for aggregation of PMMA chains in PPE/PMMA system. The mean squared displacements of monomers and whole chains describe the mobility of polymers in various systems.A coarse-grained (CG) molecular simulation model has been refined for poly (2,6-dimethyl-1,4-phenylene ether) (PPE). This was successfully validated against atomistic simulation and experimental data. Particularly, the glass transition temperature (Tg) of PPE was studied using both atomistic and CG models and compared favorably to experimental data. In addition, we used the CG model together with an existing Martini CG model of polystyrene (PS) to study the blending behavior of these two polymers. We solved the problem to mix the different potentials and molecular dynamics of high-molecular-weight blends of PPE/PS was performed in detail.