Preparation Of Well-defined PMMA/SiO₂ Composite Particles Through Atom Transfer Radical Polymerization

Nanostructured polymer/inorganic composite materials combine both the properties of the inorganic nanoparticles and those of the polymers. However, the exploitation of these properties requires a homogenous dispersion of the particles in the polymer matrix. The good way to avoid particle agglomeration is to covalently graft polymer chains onto the particles. To control the grafted polymer structure, atom transfer radical polymerization (ATRP) was introduced.The goal of this thesis work was to prepare the well-defined PMMA/SiO₂ composite particles through ATRP. Specifically, graft the ATRP initiator, 4-(chloromethyl)phenyltfimethoxysilane (CMTMS), to the silica particle surface, and then initiate the ATRP of MMA from the particle surface.Firstly, the effects of the solvent polarity and different ligands on the control of ATRP of MMA initiated by free CMTMS are discussed. This part of work helps us know well about ATRP and helps to choose proper solvents and catalyst systems for the ATRP of MMA from the particle surface. The results indicate that solvent polarity and solubility of catalyst complex in solvents affect the controllability of ATRP very much. For the ATRP of MMA initiated by CMTMS, using DMF as solvent, bpy as ligand (M_wM_n = 1.35) or xylene as solvent, PMDETA as ligand (M_w/M_n=1.30), the controllability is relatively good.Secondly, the grafting of CMTMS to the surface of SiO₂ particles is presented. The FT-IR spectrum and the element analysis demonstrate that CMTMS was successfully grafted to the surface of particle surface through covalent, and the grafting density is 0.107mmol/g (SiO₂).Thirdly, the synthesis and characterization of well-defined PMMA/SiO₂ composite particles are described. The controllability of ATRP of MMA initiated by CMTMS grafted to the SiO₂ particle surface is different from the polymerization initiated by the free CMTMS. This is because of the nature of SiO₂ particles and the immobilization of CMTMS. When use xylene as solvent, bpy as ligand, the polymerization system ([MMA] / [SiO₂-CMTMS] / [ CuCl] / [bpy] =300/1/1/2, V(MMA)/V(xylene) =3/7) is controllable (M_w/M_n=1.36). DSC, TGA, TEM and DLS were used to characterize the well-defined PMMA/SiO₂ composite particles synthesized in the above system. From thermal analysis (DSC, TGA), it is known that the thermal properties of the composite particles is much improved. The initially degradation of well-defined PMMA/SiO₂ composite particles (250℃) prepared through ATRP is nearly 50℃higher than that of the PMMA/SiO₂/CaCO₃ composite particles (200℃) synthesized through the traditional radical polymerization. The dispersion of the PMMA/SiO₂ composite particles in the organic solvents is much better than that of the SiO₂ particles, and the bigger the PMMA grafting density is, the better the dispersion is.Meanwhile, in the preparation of well-defined PMMA/SiO₂ composite particles, we found, for the first time, that MMA and BMA can be successfully polymerized in the presence of DMF without adding any other reagent. It is thought that this new type of polymerization is a radical mechanism polymerization. Ongoing efforts in our research group are seeking to expand the scope and to probe the mechanism of the polymerizations of vinyl monomers in the presence of DMF. This will opens up a new field for further investigation on polymerization of vinyl monomers.