Dispersion Polymerization Mediated By Bi-/tetra-functional Macro-RAFT Agent

Block copolymer nano-assemblies have gained great attention due to their applications in drug delivery,biochemistry,materials and so on.Of all the block copolymer,the BAB linear block copolymer and unlinear star block copolymer are synthesized relatively complexly.In this thesis,a bifunctional macro-RAFT agent of bis?trithiocarbonate?-terminated poly?4-vinylpyridine??TTC-P4VP-TTC,in which TTC represents the RAFT terminal of trithiocarbonate?and star shaped tetrafunctionalmacro-RAFTagentoftetra?trithiocarbonate?-terminated poly?N-isopropylacrylamide?[?PNIPAM-TTC?₄]were used in the dispersion polymerization of styrene?St?under PISA condition.Well-defined BAB triblock copolymernano-assembliesof polystyrene-block-poly?4-vinylpyridine?-block-polystyrene?PS-b-P4VP-b-PS?and?AB?₄four-armstarblockcopolymernano-assembliesof[poly?N-isopropylacrylamide?-block-polystyrene]₄[?PNIPAM-b-PS?₄]were prepared.This thesis can be devided into two sections as discussed below.1.In situ synthesis of BAB triblock copolymer nano-assemblies of PS-b-P4VP-b-PSIn this section,well-defined BAB triblock copolymer nano-assemblies of PS-b-P4VP-b-PS were in situ synthesized by RAFT dispersion polymerization under PISA condition.The preperation includes?1?the initial synthesis of the bifunctional macro-RAFT agent of TTC-P4VP-TTC by solution polymerization using didodecyl-1,4-phenylenebis?methylene?bistrithiocarbonate?DCTBTCD?as chain transfer agent,and?2?the subsequent TTC-P4VP-TTC mediated dispersion polymerization of styrene to prepare PS-b-P4VP-b-PS triblock copolymer nano-assemblies under PISA condition.It is investigated about the kinetics of the RAFT dispersion polymerization and the morphology evolution of PS-b-P4VP-b-PS triblock copolymer nano-assemblies with the monomer conversion.It is found that the nano-assemblies are transform from nanospheres to worms,to vesicles,to lacunal nanospheres with the extension of the PS block.The effect of polymerization degree?DP?of TTC-P4VP-TTC on the morphology of PS-b-P4VP-b-PS was also investigated.A comparatively study on the morphology of the block copolymer nano-assemblies prepared through the monofunctional macro-RAFT agent of trithiocarbonate-terminated poly-?4-vinylpyridine??P4VP-TTC?and bifunctional macro-RAFT agent TTC-P4VP-TTC mediated dispersion polymerization,respectively.To the best of our knowledge,this bifunctional macro-RAFT agent mediated dispersion polymerization was original and was not reported previously.2.In situ synthesis of thermoresponsive?AB?₄ star block copolymer nano-assemblies of?PNIPAM-b-PS?₄.In this section,well-defined?AB?₄ star block copolymer nano-assemblies of?PNIPAM-b-PS?₄ were in situ synthesized by RAFT dispersion polymerization under PISA condition.The synthesis include?1?the initial preparation of?PNIPAM-TTC?₄ macro-RAFT agent with four functional moieties by solution RAFT polymerization using 1,2,4,5-tetrakis-?butyltrithiomethyl?benzene as chain transfer agent,and?2?the subsequent in situ synthesis of?PNIPAM-b-PS?₄ four-arm star block copolymer nano-assemblies through the?PNIPAM-TTC?₄ mediated dispersion polymerization of St.The kinetics of the RAFT dispersion polymerization and the effect of PS and PNIPAM chain-length on the morphology of?PNIPAM-b-PS?₄ nano-assemblies were investigated.As PNIPAM was a typical thermoresponsive chain,a study on the thermorepsonse of?PNIPAM-b-PS?₄nano-assemblieswasmadebycomaparedwithlinear poly?N-isopropylacrylamide?-block-polystyrene?PNIPAM-b-PS?.It is found that the LCST of star PNIPAM chains tethered on the PS core is lower than that the linear PNIPAM chains under the same DP and condition.To the best of our knowledge,this may be the first example on synthesis of well-defined?AB?₄ 4-arm star block copolymer nanospheres under PISA condition,and this work may also be helpful to investigate how the topology of PNIPAM affects its thermo-responsive phase transition.