Preparation Of Functional Miktoarm Star-block Copolymers Via Combination Of Lfrp And "Click Chemistry" Techniques

Compared with linear polymers, star polymers have notable differences on surface structure, solution properties and so on. Traditionally, the miktoarm star polymers were prepared by living ionic polymerization (mainly anionic polymerization); however, both of the strict reaction conditions and poor functional group resistance of the ionic polymerization limited its application. Recently, the advances in living free radical polymerization (LFRP) techniques facilitated the synthesis of miktoarm star polymers with predetermined structures, which mainly included atom transfer radical polymerization (ATRP), nitroxide-mediated radical polymerization (NMRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, and single-electron transfer mediated living radical polymerization (SET-LRP). However, it is still difficult to synthesize miktoarm star polymers via one LFRP technique due to the limited range of monomer to be polymerized in some cases. So the combination of different LFRP methods or combination of them with other techniques, such as ring opening polymerization (ROP), living anionic polymerization and"click chemistry", was employed to prepare novel miktoarm star polymers.Our work in this thesis can be summarized as follows:(1) Preparation of well-defined Miktoarm Star Block Copolymers PSn-b-PVAc4-n via Combination of ATRP and RAFT Polymerization. Three tetrafunctional bromoxanthate agents (Xanthate3-Br, Xanthate2-Br2 and Xanthate-Br3) were synthesized. Initiative atom transfer radical polymerizations (ATRP) of styrene (St) or reversible addition-fragmentation chain transfer (RAFT) polymerizations of vinyl acetate (VAc) proceeded in a controlled manner in presence of Xanthate3-Br, Xanthate2-Br2 or Xanthate-Br3, respectively. The miktoarm star block copolymers containing polystyrene (PS) and poly(vinyl acetate) (PVAc) chains, PSn-b-PVAc4-n (n = 1, 2, 3), with controlled structures were successfully prepared by successive RAFT and ATRP chain-extension experiments using VAc and St as the second monomers, respectively. The architecture of the miktoarm star block copolymers PSn-b-PVAc4-n (n = 1, 2, 3) were characterized by GPC, 1H NMR spectra. Furthermore, the results of the cleavage of PS3-b-PVAc and PVAc2-b-PS2 confirmed the structures of the obtained miktoarm star block copolymers.(2) Synthesis of (PS)m-b-[(PgMA-g-PS)_n]_(4-m) by Combination of SET-RAFT and"Click Chemistry". According to the references, we synthesized a linear initiator (PBr) and a star initiator (PPPBr) in advance, and then used PBr and PPPBr as initiators; the comb copolymers have been successfully prepared via a one-pot/one-step technique combining SET-RAFT and"click chemistry"methods.