Degradable Multisegmented Polymer Synthesized By Consecutive Radical Addition-Coupling Reaction Of α,ω

Multisegmented polymer has unique properties and wide application, and its synthetic method is an attractive topic in polymer synthesis. In this thesis, a consecutive radical addition-coupling (RAC) reaction involving dithioester is applied to prepare degradable multisegmented polymer using a, ω-dibromo polymer as precursor.Three dithioesters were synthesized and characterized by NMR, MS. The reaction between dithioester and a, co-dibromo polystyrene (Br-PS-Br) promoted by Cu/ligand was studied and multisegmented polymer with unimodal molecular weight distribution (MWD) can be prepared by ethyl dithiobenzoate (EDTB) and Br-PS-Br.The mechanism of reaction between EDTB and Br-PS-Br promoted by Cu/ligand was investigated. The molecular weight of product gradually increased with reaction time and the MWD finally transformed to unimodal, which indicates the multisegmented polymer was generated via step-growth mechanism. The macroradical generated by single electron transfer process promoted by Cu/ligand from Br-PS-Br can efficiently add to EDTB, which results intermediate adduct radical. The in-situ formed adduct radical immediately undergoes cross-coupling reaction with macroradical, generating segmented polymer bridged with C-S bond. Incorporation of dithioester into the multisegmented polymer chain was also confirmed by1H-NMR/13C-NMR spectra, thermal fragmentation and deprotection of S, S-ketals.The influences of temperature,[EDTB]0/[Br-PS-Br]o ratio, Br-PS-Br concentration, and the macroradical generation rate on the RAC of a, co-dibromo polystyrene and EDTB were investigated. As the temperature increased, the rate of RAC and cross-coupling efficiency (CCE) increased. It was found that when [EDTB]0/[Br-PS-Br]o ratio increased from1/1to5/1, CCE increased significantly. When a5-fold excess of EDTB compared to Br-PS-Br was employed, the CCE can reach93.2%. When the Br-PS-Br reaction concentration increased, the CCE and the molecular weight of the multisegmented polymer have no significant changes, but the molecular weight distribution was broader. In addition, the macroradical generation rate has a certain influence on the RAC.The reaction between EDTB and monobromo poly(tert-butyl acrylate)(PtBA-Br) was studied, and the efficiency of the RAC is low. For PtBA-Br/PS-Br/EDTB reaction system, a PS-PtBA diblock product could be obtained, which suggests that the low efficiency of RAC of PtBA-Br was mainly due to the low coupling tendency of its radical.