Synthesis Of Polymer Microspheres By RAFT Precipitation Polymerization

An acrylate monomer containing two hydroxyl groups,2,2-bis(hydroxymethyl)butylacrylate (HBA), was successfully synthesized by the reaction of acryloyl chloride and2,2-dimethyl-5-ethyl-5-hydroxymethyl-1,3-dioxane (DEHD) followed by acidic hydrolysis.The reversible addition-fragmentation chain transfer (RAFT) polymerization of monomerprecursor,(5-ethyl-2,2-dimethyl-1,3-dioxane-5-yl)methyl acrylate (EDMA), as well as HBAwas performed in dioxane using2,2′-azobis(isobutyronitrile)(AIBN) as initiator and2-(ethylthiocarbonothioylthio)-2-methyl propanoic acid (EMP) as the chain transfer agent.Kinetic studies demonstrated that the polymerization process of both monomers followedpseudo first-order kinetics with respect to the monomer concentrations and EDMA wasconsumed at a higher rate than the HBA over a given time. The molecular weight of theresulting polymer increased linearly with monomer conversion, while a low polydispersity wasmaintained throughout. After polymerization, the dioxane groups of poly(EDMA) weredeprotected to form1,3-diol groups, yielding poly(HBA).A facile and one-pot approach is developed here to synthesize narrow or monodisperse,highly cross-linked polymer microspheres. This approach is based on RAFT polymerizationand precipitation polymerization, which allows the direct generation of uniformly cross-linked“living” polymer microspheres. The polymerization parameters (including monomer loading,initiator and RAFT agent concentrations, molar ratio of cross-linker to vinyl monomer, andpolymerization scale and time) have been studied. The applicability of RAFT precipitationpolymerization (RAFTPP) was demonstrated by synthesizing of polymer microspheres withdifferent vinyl monomers (i.e., EDMA, and HBA) and identical cross-linker, ethylene glycoldimethacrylate (EGDMA). Moreover, the “livingness” of the resulting polymer microsphereswas confirmed by their direct grafting of hydrophilic polymer brushes via surface-mediatedRAFT polymerization.