Preparation Of Fluorinated Acrylate Block Copolymers By RAFT Polymerization And Their Self-Assembly Studies

Polymeric microspheres is a kind of new functional polymer materials with double-layer structure, due to its composition and nature of diversity, compare to the materials having large surface area, therefore widely used in drug loading and controlled release, catalyst loading, nano reactors and other fields. Because of the introduction of fluoride chain segment, these copolymer microspheres shows excellent biological compatibility, thermal stability, low surface energy, etc.A series of fluorinated block copolymer microspheres were synthesized via reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization in supercritical carbon dioxide (scCO2). In the process of synthesizing fluoropolymer, supercritical carbon dioxide (scCO2) has been proved as an excellent polymerization medium containing properties like nontoxicity, fast mass and heat transfer rate, chemical inertness, easy purification of products, excellent dispersibilty, good solubility, cost effectiveness and most importantly can be used as a green polymerization medium instead of conventional hazardous organic solvents. This investigation reports the preparation of a series of poly(dodecafluoroheptyl methacrylate-cumyldithiobenzoate) (PDFMA-CDB) homopolymers with various chain lengths by using RAFT polymerization, where cumyldithiobenzoate (CDB) was used as RAFT agent. This PDFMA-CDB was later used as macromolecular chain transfer agent for RAFT dispersion polymerization of methyl methacrylate (MMA) as well as N-isopropylacrylamide (NIPAM) in supercritical carbon dioxide to prepare monodisperse fluorinated diblock copolymer microspheres PDFMA-b-PMMA and PDFMA-b-PNIPAM respectively. The molecular weight and molecular weight distribution (PDI) were measured by GPC. The chemical structures and actual degrees of polymerization were investigated by FT-IR and 1HNMR. The experiment results showed that the chain transfer agent CDB was a suitable chain transfer agent of DFMA RAFT polymerization and can be use to synthesize a series of different degree of polymerization fluorinated homopolymer chain transfer agent. Highly monodisperse fluorinated block copolymer microspheres were obtained by adjusting the chain length of the second block PMMA and polymerization reaction pressure. SEM results showed that aggregation morphologies for diblock copolymer PDFMA-b-PMMA obtained in CO2 varied from irregularly conglomeration to monodisperse microspheres with the increase of MMA block length. It can be explained considering that PDFMA-CDB block chains might be better CO2-philic and would be better able to diffuse when the length of PDFMA-CDB became longer. The diblock copolymer PDFMA-b-PMMA was self-assembled in (THF)/H2O system. X-ray photoelectron spectroscopy (XPS) analysis showed the formation of the microspheres in supercritical CO2 based on PMMA and PNIMPAM as core and PDFMA as shell. A series of different degree of polymerization of PDFMA-b-PNIPAM diblock copolymers microstructure were characterized by SEM. The results showed that the dispersion polymerization of MMA with respect to the dispersion polymerization of NIPAM in supercritical carbon dioxide is much easier to self-assemble into microspheres, and by increase in the degree of polymerization of NIPAM, the size of microspheres decreased.