Synthesis Of Triblock Terpolymers Via ATRP And Their Preparation Of Janus Micelles By Self-assembly

Janus particles are structurally asymmetric particles of different polarity withdifferent chemical composition, as a new class of materials they have broad applicationprospects in the fields of biomedical science, aerospace and functional materials.Currently, there are many preparation methods to obtain Janus particles includingselective surface modification, self-assembled template, topological surfacemodification, microfluidic control, etc., but such drawbacks as low productionefficiency, less control over the diameter and polydispersity are issues attachingimportance. This paper prepared Janus micelles using self-assembly of tri-blockterpolymer, which exerted a more facile preparation approach to obtain nanoscaledJanus micelles with controlled distribution.Firstly, two series of triblock terpolymer polystyrene-b-poly(diethylaminoethylmethacrylate)-b-poly (methyl methacrylate)(PS-b-PDMAEMA-b-PMMA) andpolystyrene-b-(diethylaminoethyl methacrylate)-b-poly (t-butyl methacrylate)(PS-b-PDMAEMA-b-PtBMA) were synthesized via continuous Atom Transfer RadicalPolymerization (ATRP) method. Using styrene (St) as the monomer, α-bromo ethylisobutyrate (EiB-Br) as the initiators, CuBr/PMDETA as the catalyst system,macroinitiator poly styrene (PS-Br) was synthesized by bulk polymerization, then usingPS-Br as the macro-initiator to conduct the bulk polymerization of second monomerdimethylaminoethyl methacrylate (DMAEMA) to obtain PS-b-PDMAEMA-Br diblockcopolymer, followed by using PS-b-PDMAEMA-Br as the macro-initiator torespectively conduct bulk polymerization of the third monomer methyl methacrylate(MMA) and tert-butyl methacrylate (tBMA) to obtain a tri-block terpolymer PS-b- PDMAEMA-b-PMMA and PS-b-PDMAEMA-b-PtBMA. The results showed thatwhen reaction time is controlled, the degree of polymerization and the molecular weightof PS-Br, PS-b-PDMAEMA-Br, PS-b-PDMAEMA-b-PMMA and PS-b-PDMAEMA-b-PtBMA increased linearly with the increasing of the molar ratio of the monomer andthe initiator, the narrow molecular weight distribution indicated that the reaction has agood controllability.Then the tri-block terpolymer was selectively hydrolyzed to form amphiphilic tri-block terpolymer polystyrene-b-poly (diethylaminoethyl methacrylate)-b-poly(methylacrylic acid) PS-b-PDMAEMA-b-PMAA by an acidic hydrolysis of the PS-b-PDMAEMA-b-PMMA and PS-b-PDMAEMA-b-PtBMA. Surface activity of thehydrolyzed amphiphilic triblock terpolymer was studied. The results showed that it hasa certain surface tension reducing ability in aqueous solution, but weaker than stearicacid small molecule surfactants.This paper also investigated the self-assembly behavior of PS-b-PDMAEMA-b-PMMA and PS-b-PB-b-PMMA in selective solvent systems. The pre-assembledmicelles of PS-b-PDMAEMA-b-PMMA sized around10nm were formed with the coreconsisting of PDMAEMA block and the corona consisting of PS and PMMA blocks ofpatchy separation in CH2Cl2, the multicompartment micelles sized around100nm to300nm were prepared after dialyzed against C6H12, the core of PDMAEMA block wasstacked with the PMMA block collapsed from the reduced solubility in the selectivesolvent. Similarly, the pre-assembled micelles of PS-b-PB-b-PMMA sized around25nm were formed in DMAc, and the multicompartment micelles sized around45nmwere prepared by dialyzed against the mixture of acetone/isopropanol. The ratio of theacetone/isopropanol exerted little effect on the shape and micro-phase segregation ofmulticompartment micelles indicating high structural stability of the micelles prepared.After the photo-crosslinking of the PB segment, and finally dialysis to the co-solventto form the Janus particle which diameter is about20nm.