Controllable Synthesis Of Poly(Styrene-co-γ-methyl-α-Methylene-γ-butyrolactone)-b-poly(n-butyl Acrylate)-b-Poly(Styrene-co-γ-methyl-α-methylene-γ-butyrolactone) With Uniform Composition Profile On Hard Blocks Via RAFT Emulsion Polymerization

The reversible addition fragmentation chain transfer (RAFT) emulsion polymerization has been shown to be a new green energy-saving method to synthesize copolymers. In addition to the copolymer composition, the copolymer composition profile will also greatly influence the properties of copolymer. In the current thesis, we synthesized the thermoplastic elastomer (TPE) of well-defined poly(styrene-co-y-methyl-a-methylene-y-butyrolactone)-b-poly(n-butyl acrylate)-b-poly(styrene-co-y-methyl-a-methylene-Y-butyrolactone)(S/M-nBA-S/M) with uniform compositional profile along copolymer chains in a monomer feeding semi-batch RAFT emulsion polymerization using the PAA2o-PSt5-RAFT as both surfactant and mediator. We studied the influence of the compositional profiles of S/M blocks on mechanical properties at high temperature of the TPE. We came to the following conclusions:i). The S/M copolymer with the uniform composition profile could be synthesized by exploiting the following semi-batch monomer feeding policy:adding all the relatively inert monomer (St) and part of the relatively active monomer (MeMBL) at the beginning of the reaction, then adding the rest of the MeMBL to the reaction system with variable feeding rates. It was found that the uniform composition profile led to the gel effect in the late stage of the emulsion polymerization, causing dramatic increase in PDI. Mixing a small amount of methylbenzene with the initially charged monomers and raising the reaction temperature up to 90℃ in the late stage of the polymerization could decrease the PDI of S/M copolymer to 1.2. To avoid the formation of a large number of dead polymers resulting from the above process, we decreased the initial initiator concentration to one in twentieth of RAFT concentration. Well defined S/M copolymer with 0.33 molar fraction of MeMBL and the uniform composition profile was synthesize successfully with the following monomer feeding policy:charging all St and partial MeMBL (33wt.% of all MeMBL) into the reactor before polymerization.(2) feeding 37wt.% of all MeMBL between 15-45min at a constant rate. (3) feeding the rest MeMBL between 45-55min at another constant rate.(ii). It was found that in the synthesis of the triblock copolymer, the seed latex must be pre-swollen by monomers prior to starting the polymerization in order to synthesize well-defined triblock copolymer. A series of S/M-nBA-S/M triblock copolymer with uniform composition profiles in S/M blocks and various compositions was prepared. CoMPared with S/M-nBA-S/M triblock copolymer with spontaneous gradient composition profile on S/M blocks, the tensile elastic modulus and yield strength of the TPEs with uniform composition profiles would decrease less with increase of temperature, suggesting that the TPEs should have the higher mechanical properties at high temperature.