Synthesis And Characterization Of PS-b-PS/Bu-b-PS Block Copolymers Via RAFT (Mini)emulsion Polymerization

Anionic polymerization is the most used method industrially which can synthesize a variety of copolymers with different structures. However, anionic polymerization requiring removing water and oxygen is usually performed in solvent and lower temperature and the polymerization condition is very rigorous. Moreover, anionic polymerization method is only fit for some very few monomers, for example, styrene and butadiene. Reversible Addition-Fragmentation chain Transfer(RAFT) (mini)emulsion polymerization was an environmental friendly, energy saving for most monomers, considered to be one of the most prominent "living"/controlled free radical polymerization from both industrial and commercial perspectives.To prepare the toughened styrene/butadiene block copolymers, RAFT (mini)emulsion polymerization method was acquired to get PS-b-PS/Bu-b-PS block copolymers with different molecular structure and composition, butadiene seeded miniemulsion polymerization mediated by PS-PEPDTA macromolecular RAFT agent was performed and RAFT binary monomers (mini)emulsion copolymerization kinetic model was established. PS-b-PS/Bu-b-PS block copolymers were synthesized by feeding strategy of model control. Synthesis kinetics and relationship between its properties and microphase morphology was explored.The styrene and butadiene RAFT polymerization were researched firstly. Styrene RAFT bulk and miniemulsion polymerization kinetics were performed with PEPDTA. For styrene bulk RAFT polymerization, the retardation was not obvious. For styrene RAFT miniemulsion polymerization, the induction period and retardation were more prominent with PEPDTA concentration increased, and the polymerization rate was much faster than the counterpart. Meanwhile, the number of particles decreased and its distribution became broader. The molecular weight increased linearly along with the increasing of conversion, and its molecular weight distribution became much narrower when PEPDTA increased. The theoretic modeling curves formulated were approaching to the experimental data, and RAFT miniemulsion polymerization kinetic model based on the Smith-Ewart equation well predicted the experimental processes. Butadiene RAFT seeded miniemulsion polymerization was mediated by macromolecular PS-PEPDTA RAFT agent. The results indicated that retardation was prominent, and molecular weight increased linearly along with the increasing of conversion with its molecular weight distribution being much narrower when PEPDTA concentration increased., and the function between polymerization index and time was linearly, which meaning "living"/controlled polymerization. The equilibrium constant between butadiene and PEPDTA was calculated, which was 18.3L/mol·s, which was an important parameter in styrene/butadiene RAFT copolymerization kinetics.RAFT binary monomers (mini)emulsion copolymerization kinetic model was established, calculating monomers'conversion, Mn and composition of the copolymers, which could predict the copolymerization process. PS-b-PS/Bu diblock copolymers with Mn=20,300-45,200g/mol, PDI=1.28-1.45 and different macromolecular architectures and composition were synthesized via RAFT batch or semibatch (mini)emulsion polymerization. FT-IR and 1NMR results indicated that the microstructure of the polymer was mainly 1, A-trans butadiene with small amount of 1,2-units, and composition in the copolymers was obtained. GPC curves of molecular weight distribution function(dwt/dlogM) remained single modal distribution, and nearly symmetrical, showing the typical characteristics of "living"/controlled radical polymerization. Its molecular weight distribution became broader while increasing its molecular weight. In order to obtain different styrene/butadiene block composition and be well controlled during styrene/butadiene RAFT (mini)emulsion copolymerization process, it was important to explore its mechanism and kinetic modeling. The theoretical modeling curves of monomers' conversion, molecular weight and composition of the copolymers were close to the experimental data, which could well predict the copolymerization process. Furthermore, the composition in S/Bu block was uniformed or tapered in these reaction systems, when butadiene feeding was batch or semibatch process, respectively.A series of PS-b-PS/Bu-b-PS triblock copolymers with volume fraction of PS between 0.64-0.80 were synthesized via RAFT (mini)emulsion polymerization, based on feeding technology of styrene and styrene/butadiene RAFT (mini)emulsion polymerization kinetic models. Numerical molecular weight of the copolymers was from 38,300 to 82,000g/mol, and its distribution from 1.40 to 1.92. And fractions of butadiene in S/Bu block were tapered, uniformed and combined structures, respectively. It was demonstrated that kinetic models could well predict the polymerization process. Molecular weight and structure of PS-b-PS/Bu-b-PS triblock copolymers were identified. And 1, 4-trans and 1,2-butadiene in the copolymers,1, 2-units proportion was about 20% of the total butadiene content.The thermal and mechanical properties of PS-b-PS/Bu and PS-b-PS/Bu-b-PS copolymers were discussed with its composition and structure. Differential scanning calorimetry(DSC) indicated that glass transition in-80～0℃was not clear, when the fraction in S/Bu block was tapered. On the other hand, the counterpart was prominent, when the fraction in S/Bu block was uniformed or polybutadiene block. The tensile properties of PS-b-PS/Bu diblock copolymers were low, mainly because of lower molecular weight. The molecular weight of PS-b-PS/Bu-b-PS copolymers between 70,000-80,000g/mol with the nearly same PS fraction were extruded, the integration between stress and strain meaning a measure of energy absorption, sample 8 was the highest in all samples, due to its lamellar microphase morphology and the narrowest width of interface.Synthesis and characterization of serials of PS-b-PS/Bu-b-PS copolymers were performed by feeding strategy of styrene RAFT miniemulsion and RAFT binary monomers (mini)emulsion copolymerization kinetic models based on styrene, butadiene RAFT miniemulsion copolymerization kinetics. Relationship between thermal, mechanical properties and composition, microphase morphology of the PS-b-PS/Bu-b-PS copolymers were obtained.