RAFT Dispersion Polymerization Using Bifunctional Macro-RAFT Agents

Block copolymer nanomaterials have attracted increasing attention due to their broad applications in the fields of drug delivery,Pickering emulsion,nanoreactor and hydrogels etc.Polymerization-induced self-assembly(PISA)via reversible additional-fragmentation chain transfer(RAFT)dispersion polymerization has become a versatile method for the preparation of block copolymer nanomaterials at high solids.Currently,much effort has been devoted to control the morphologies and polymer architecture during the research of PISA.In order to expand the scope of RAFT dispersion polymerization,in this thesis,we will synthesize a series of bifunctional macro-RAFT agents and employ into RAFT dispersion polymerization for the preparation of well-defined block copolymer nanomaterial.The main content of this paper is as follows.1.RAFT dispersion polymerization of DAAM in water at 70 ^oC mediated by polymerization of N,N-dimethylacrylamide(DMA)as bifunctional macro RAFT-agents was performed via either thermal initiation and photoinitiation.A variety of block copolymer nano-objects including spheres,fibers,and vesicles were prepared.The effect of initiation type(thermal initiation and photoinitiation)on the morphology of block copolymer nano-objects was studied in detail.UV-vis spectroscopy indicated that high RAFT end-group retainment was achieved regardless of initiation used.Finally,the morphological evolution and the change in particle diameter were also monitored by characterizing samples withdrawn during the kinetic study.It was found that the difference in polymerization kinetics was the main reason for the morphological difference.Finally,a novel strategy was developed by combining thermal initiation and photoinitiation in one system was developed.The polymerization kinetics was controlled by changing the period of light exposure,allowing the precise control over morphologies.2.3-(benzylthiocarbonothioylthio)propanoic acid BTPA and BTSMA were synthesized.These two RAFT agents were then linked with ethylene glycol(EG)through esterification,respectively.Difunctional RAFT agents including BTPA-EG-BTPA and BTSMA-EG-BTSMA were then synthesized and employed to mediate RAFT solution polymerization of N,N-dimethylacetamide(DMA).The obtained[PDMA₆₀-BTPA]₂and[PDMA₆₀-BTSMA]₂were then used as bifunctional macro-RAFT agents in aqueous RAFT dispersion polymerization of DAAM at 70 ^oC.ABA and BAB triblock copolymer nanomaterials were then prepared by changing reaction conditions.TEM,GPC,and DLS were used to study the effect of structure(including ABA and BAB)on polymerization kinetics and morphologies of block copolymer nanomaterials.The effect of molecular weight of macro-RAFT agents on the morphology of block copolymer nanomaterials was also investigated in detail,providing important melanistic insights.3.Seal the BDMAT side with benzyl alcohol and denoted as BDMAT-Bn.A bifunctional macro-RAFT agent was then prepared by esterification between m PEG₄₅and BDMAT-Bn,denoted as m PEG₄₅-BDMAT-Bn.This macro-RAFT agent was then employed to mediate RAFT dispersion polymerization of St in methanol/water at 70 ^oC.A series of block copolymer nano-objects with various morphologies were prepared.The morphological evolution process was monitored by characterizing morphologies of samples withdrawn during the kinetic study.m PEG₄₅-PSt_n-BDMAT-PSt_n-Bn diblock copolymer vesicles were used as seeds for seeded RAFT dispersion polymerization of isobronyl acrylate(IBOA)or N-isopropyl acrylamide(NIPAM)to prepare ABCB type block copolymer nanomaterials.TEM,DLS,and GPC were utilized to characterize the obtained ABCB type block copolymer nanomaterials.