Studies Of Reverse Atom Transfer Radical Polymerization And It's Used In Synthesizing Functional Polymers

The preparation of well-defined polymers and functional polymers by controlled radical polymerization has been an area of intense interest in recent years. In particular, atom transfer radical polymerization (ATRP), especially reverse atom transfer radical polymerization (R-ATRP) has been one of the most successful and versatile techniques by radical means.The goal of the thesis was to study the theory of R-ATRP and use this method in synthesizing functional polymers. This thesis include two big parts: (1) study of the influence of different ligands, solvents and monomers on polymerization, the goal was to consummate the R-ATRP theory; (2) using R-ATRP in synthesizing functional polymers. The main studies are as follows:1. Studies of the theory of R-ATRP, this part include three aspects:(1) Using MMA as monomer, xylene as solvent, CuBr₂ as catalyst, from measuring polymerization kinetic, polymer molecular weight (M_n) and molecular weight distribution (D), studying the controllability of MMA polymerization using different ligands, such as N,N,N',N'-teramethylethylendiamine (TMEDA), N,N,N',N',N" -penta methyldiethylentriamin (PMDETA), 2-2'-bipyridine (bpy) and 4,4'-Di(5-nonyl)-2,2'-bipyridine (dNbpy). The results shows that the polymerization using bpy as ligand represents uncontrolled. The solubility of CuBr₂/bpy complex in xylene is too low to make the polymerization be controlled. The same was to be the polymerization using PMDETA as ligand. The controllabilities of polymerization using TMEDA as ligand and using dNbpy as ligand were better. Because that the complex can be dissolved completely in solvent. But the controllability of polymerization using dNbpy as ligand was better than using TMEDA as ligand, the results can't be explained by the different solubility of complex. Our studies show that the electronic effect of ligand molecular would play the crucial role on the control of polymerization. The electrons of a big conjugated molecular will spread themselves as a group over a large section of the molecular. When it complexes with CuBr₂, the electron donating effect reduce the oxidation state (the oxidation state is not the valence state) of Cu atom and make the complex (Cu⁺¹ or Cu⁺²) more stable. So the equilibrium between the growing radical and the dormant species can be rapid established and the control of polymerization is easily to be realized. The TMEDA molecule was not a conjugated system of bonds and had not this effect, so the controllability was worse. The obtained polymer was measured by ¹H-NMR, the results show the polymerization following the R-ATRP mechanism.(2) Using MMA as monomer, bpy as ligand, CuBr₂ as catalyst, from measuring polymerization kinetic, polymer molecular weight (M_n) and molecular weight distribution (D), studying the controllability of MMA polymerization using different solvent, such as xylene, DMF and pyridine. The results show that the polymerization using xylene as solvent represents uncontrolled. The solubility of CuBr₂/bpy complex in xylene is too low to make the polymerization be controlled. The polymerizations using DMF as solvent and using pyridine as solvent were homogeneous, and the controllabilities were better than the xylene system. But the pyridine may complexes with CuBr₂ as well as bpy. The CuBr₂/pyridine complex cannot be the catalyst of controlled polymerization, much more CuBr₂ complex with pyridine would decrease the efficiency of catalyst. So the results show a not better controlled polymerization. The -N(CH₃)₂ group in DMF also complexes easily with CuBr₂. The same to pyridine, it will decrease the efficiency of catalyst. The CuBr₂/pyridine complex and CuBr₂/DMF complex could be measured by UV-vis Spectrometer. The obtained polymer was also measured by ¹H-NMR, the results show the polymerization following the R-ATRP mechanism.(3) Choosing St, BA and BMA as the monomer, xylene as solvent, from measuring polymerization kinetic, polymer molecular weight (M_n) and molecular weight distribution (D), studying the controllability of different monomers' polymerization. TMEDA, PMDETA and dNbpy were used in each monomer's polymerization. The results show that the controllabilities of BMA polymerizations using different ligands were best among the monomers, and the controllabilities of BA polymerizations were better than St. the different results came from the monomer itself. The activity of BMA radical is suitably, and the activity of BA radical is too high. During the polymerization, the BA radical is difficult to be captured by complex to form a dormant species. So the polymerizations represent uncontrolled. The St radical is a conjugated structure and very stably. It is also difficult to form a dormant species. Besides, the different monomer systems have different solubility to catalyst, it will also influence the controllabilities of polymerization. The obtained polymer was also measured by ¹H-NMR, the results show the polymerization following the R-ATRP mechanism.2. Studies of using R-ATRP method to synthesis functional polymers, this part include four aspects:(1) Using the obtained R-ATRP polymer PMMA-Br as the macro-initiator to initiate other monomers, such as St, BA and MBA by ATRP and synthesis two block polymers. The results by measuring polymerization kinetic, polymer molecular weight (M_n) and molecular weight distribution (D) show that the macro-initiator could initiate the monomers and the polymerizations are controlled. The obtained polymers were two block polymers and the structures of obtained polymers were well-defined which could be measured by ¹H-NMR spectroscopy and DSC measurement.(2) Based on the advantage of the halide end group prepared by R-ATRP, using the obtained polymer PMMA to react with the low molecular weight UV-absorber UV-0, and introduce the UV-absorber group to polymer, to endue the polymer UV-ageing resistance. Characterizations of the obtained polymer were done by UV-vis spectrometer and ¹H-NMR. The results show that UV-0 was successfully grafted to the macromolecular chain and the grafting efficiency was 25.4%. The blank PMMA and the grafted PMMA were dissolved and make films respectively, then used directly to the UV irradiation degradation. The GPC results show that the retention of M_n and D of grafted PMMA was obvious better than the blank PMMA. This method is a new idea for polymer UV-ageing resistance.(3) Using polymerizable UV-absorber, such as BPMA and MHB, to co-polymerized with MMA or St, and studying the controllabilities of co-polymerization and the structure, UV-absorbency of obtained polymers. The results of polymerization kinetic, polymer molecular weight (M_n) and molecular weight distribution (D) show that the co-polymerizations of MMA with BPMA or MHB were controlled and the co-polymerizations of St with BPMA or MHB were un-controlled. The obtained polymers were measured by ¹H-NMR, the results show that BPMA or MHB was introduced to the obtained polymers. Comparing the feeding ratio, more BPMA or MHB was introduced to the obtained polymers by calculating the ²H-NMR peak area integral, this maybe relate to the Characterizations of BPMA and MHB. Furthermore, the Tg of obtained polymers were measured by DSC, The results show that the Tg of MMA co-polymers with BPMA or MHB have obvious increasing, because the rigidity benzene ring was introduced to PMMA. On the contrary, the Tg of St co-polymers with BPMA or MHB have obvious decreasing, the reason was the BPMA or MHB group in the main chain act as the softener which made the Tg to decrease. All the obtained co-polymers have obvious UV-absorbency measured by UV-vis spectrometer.(4) Primary study of R-ATRP in emulsion. The results of measuring polymerization kinetic, polymer molecular weight (M_n) and molecular weight distribution (D) show that the increasing of monomer conversion of R-ATRP in emulsion was obvious different to general emulsion, the increasing of polymer molecular weight was also slowly than general emulsion. In primary stage, the polymerization was not controlled, and then the polymerization was controlled gradually. The ¹H-NMR spectrums revealed the presence of a bromine atom end group of obtained polymer, the polymerization following the R-ATRP mechanism. The controlled polymerization mechanism of R-ATRP in emulsion is more complicated than that in solution because the emulsion system is multiphase compared with solution system. The ratio of CuBr₂ in oil phase was measured using UV-vis spectrometer by our designed experiment, the results show that CuBr₂ enter into the micelle with the polymerization and reach a constant value gradually. This results answer for the experiment results. Scanning Probe Microscope image shows the shapes of the final polymer particles are global and the diameters of the particles are in the range of 60-100nm. This study established a experimental foundation for the application of R-ATRP in emulsion.