Synthesis And Solution Behavior Of Amphiphilic Multiblock Copolymers

Self-assembly of copolymer is one of the hottest subjects in polymer science now. Due to the potential applications of chemical and biological sensor,drug delivery and other many fields,it has been received increasing attention.In this paper,multiblock poly(tert-butylacrylate)containing various trithiocarbonate groups per chain were synthesized via reversible addition-fragmentation transfer(RAFT)polymerization with 4,7-diphenyl-[1,3]dithiolane-2-thione(DPDTT)as RAFT agent.Two amphiphilic multiblock copolymers,[poly(N-isopropylacrylamide)-b-poly(tert-butylacrylate)-bpoly (N-isopropylacrylamide)]_n(PNIPA-b-PtBA-b-PNIPA)_n and [poly(N-isopropylacrylamide)-b,poly(styrene)-b-poly(N-isopropylacrylamide)]_n (PNIPA-b-PS-b-PNIPA)_n were then prepared by using multiblock poly(tert-butylacrylate)as Macro-RAFT agent.The self-assemble behaviors of these amphiphilic multiblock copolymers in organic or aqueous solutions were then systematically investigated by using TEM,AFM and DLS techniques.It was found that the micelles of(PNIPA-b-PtBA-b-PNIPA)_n changed from short rod into huge spherical micelle as the content of water in the THF/water mixed solvent increased.Due to the thermo-sensitive character of PNIPA block,the hydrodynamic diameter of the micelle decreased with increasing temperature.This behavior was reversible.For(PNIPA-b-PS-b-PNIPA)_n,it formed spherical like micelles in THF/water mixed solvent.The size of micelle was also increased with raising the water content in the mixed solvent.Interesting,the hydrodynamic diamter of micelle was first decreased with increasing the temperature blow the LCST of PNIPA,while further increased when temperature rise above the LCST.We also investigated the micellar behavior of a series of amphiphilic multiblock copolymer(P4VP-b-PS-b-P4VP)_n,with various block length of the P4VP block in toluene/DMF mixed solvent.It was found that increasing the length of P4VP block, the micelle morphology changes from worm-liked to spherical shape.The initial concentration of the block copolymer also affected the micelle morphology.At low concentration,isolated spherical micelles were observed for S₁₀₆4VP₁₆₆,while rod-like micelles were formed at high concentration.Additionally,the different solvent will have different effects on the size and morphology of the micelles.