Synthesis Of Silicon Containing Diblock Copolymer Via Reversible Addition-Fragmentation Transfer Polymerization And The Investigation Of Its Self-Assembly Behavior

Thanks to the establishment of "living"/controlled radical polymerization technology, a much larger variety of monomers than ever before can be employed to synthesize block copolymer with particular properties, now. In this thesis, a new kind of diblock copolymer, one block of which is derived from alkoxysilane monomer, was designed and synthesized. Nano-structures materials could be achieved by self-assembling the synthesized block copolymer. Organic/inorganic hybrid materials with various nano-structures could be accessible by a template sol-gel process of alkoxysilane.γ-methacryloxypropyltrimethoxysilane (MPMS) andγ-methacryloxypropyltriethoxysilane (MPES) were selected as alkoxysilane monomers to copolymerize with methyl methacrylate (MMA) to form diblock copolymers via reversible addition-fragmentation transfer (RAFT) polymerization. The homopolymerization of MMA, MPMS and MPES was effectively controlled by the 2-cyanoprop-2-yl dithiobenzoate (CPDB), used as the RAFT agent. During the polymerization, the number averaged molecular weight increased linearly with the conversion and the polydispersivity index (PDI) remained at a low level (except for some cases caused by hydrolysis and condensation), indicating a well-living/ controlled polymerization. In the case of MPMS, the methoxysilane groups incorporated in the polymer chains as side groups easier take reactions of hydrolysis and condensation during the polymerization than ethyloxysilane in MPES. As a result, a small fraction of the branching polymer was formed, increasing the PDI values. However, MPES did not have such a problem. The problem with MPES is that the polymerization proceeds slower. Using the initiators with longer half-life, high concentration of monomers, and high reaction temperature were employed to improve the polymerization rate.Both results from differential scanning calorimeter (DSC) and transmission electronmicroscope (TEM) showed that the microphase separation occurred in the diblock copolymer of methyl methacrylate and γ-methacryloxypropyltrimethoxysilane (PMMA-b-PMPMS), but the separation was not complete, because the reactions hydrolysis and condensation also took place during the microphase separation, which hindered phase separation. However, typical microphase separation structures were observed in the bulk of diblock copolymer of methyl methacrylate and γ-methacryloxypropyltriethoxysilane (PMMA-b-PMPES), of which the dispersed phase was PMMA with the shape of cylinder having the diameter around 20 nm and continuous phase was PMEMS with the characteristic dimension around 10 nm. we also explored the self-assembly structures formed by PMMA-b-PMPMS using mini-droplets as template under different pH values. From the TEM images, different self-assembly structures were observed in different pH values. In the acid system, large particles with the diameters of hundreds of nanometers were formed, in which finer nano-structures were clearly seen. In the neutral system, only uniform particles with the diameters of tens of nanometers were formed. In the basic system, large particles with the diameters of hundreds of nanometers were formed, which contain radial fibers.