ScCO ₂ In RAFT Prepared Fluoroalkyl Acrylate Polymers

The structural characteristics of the fluorinated polymers (FPs) endow them excellent properties and extensive application prospects. Among FPs the fluorinated amphiphilic block copolymers are of great importance in surface modification, protective coating, lubrication and emulsion preparation due to their distinctly low surface energy. Recently, supercritical carbon dioxide (scCO2) is increasingly accepted as a green medium and expected to be the most promising alternative of the organic solvents. The research and application of scCO2will attribute great to lower contaminants to environment and the consumption of energy, lower cost, develop new reaction system, and thus promote the sustainable development of FPs. Reversible addition fragmentation chain transfer (RAFT) polymerization is a kind of typical living/controlled free radical polymerization method, and is also an effective strategy for polymer design due to its good compatibility of monomers and moderate reaction conditions.By feat of the advantages of the fluorinated amphiphilic block copolymers, as well as the RAFT method, two dithioester RAFT agents were designed and synthesized in this dissertation. The performance of the RAFT agents were evaluated based on the reactivity to the objective/model monomer (s), so as to choose the proper RAFT agent for the target monomer of fluorine alkyl acrylate(s). The selected RAFT reagent was used in the synthesis of the homopolymer and diblock copolymer of the target monomer(s) in scCO2. The self-assembly/aggregation behaviors of the prepared amphiphilic block copolymers were preliminary invesitaged. This research work is expected to promote the controlled polymerization of the fluorinated alkyl acrylate monomers in scCO2, and also promote the further application of the prepared FPs in many fields.The main work is summarized in3parts as follows:(1) Preparation, characterization and reactive performance verification of the RAFT agents.Two RAFT agents of benzyl dithiobenzoate (BDB) and cumyl dithiobenzoate (CDB), which were expected to fit for polymerization the target monomer(s), were designed and prepared. The prepared BDB and CDB were employed in the free radical polymerization of AA and TFEMA. In this way the expected polymers were prepared with a RAFT fragment in their chain end. The chemical structure of the prepared polymers were characterized by FT-IR and1H-NMR, and the molecular weights and the molecular weight distribution were characterized by GPC. The results show that CDB and BDB can control the free radical polymerization of the above monomers to some extent, but there are different regulation performance for the monomers. For the objective monomer, especially the fluorinated alkyl acrylate, CDB shows better control performance to BDB, and it is expected to be the proper RAFT agent for the polymerization of the fluorinated alkyl acrylate in scCO2. Such hypothesis is further verified as PTFEMA-b-PAA were successfully synthesized.(2) Preparation and characterization of PHFBMA in scCO2.Poly(hexafluorobutyl methacrylate)(PHFBMA) was synthesized via RAFT method in scCO2, The variation of monomer conversion with reaction time was investigated by’H-NMR and high pressure in situ infrared spectroscopy (FT-NIR) technology, and the molecular weights as well as the molecular weight distribution were characterized by GPC. The impact of RAFT dosage on monomer conversion as well as the molecular weight was also studied. It is found that the monomer conversion decreased with the increase of CDB concentration, while there is still an approximately linear relationship between the molecular weight and the conversion, indicating that CDB is an effective chain transfer agent in the free radical polymerization of HFBMA.(3) Fluorinated amphiphilic block copolymers preparation and their self-assembly behaviors investigation.Different amphiphilic diblock copolymers of PHFBMA-b-PAA with various PHFBMA/PAA molar ratios were synthesized by two-step-one-pot reaction in scCO2using PHFBMA-CDB as a macro-RAFT agent. The polymer were characterized by FT-IR,1H-NMR and TGA/DSC. The self-assembly behaviors were preliminary studied via the surface tension meter, dynamic light scattering (DLS), and transmission electron microscopy (TEM). The CMC of the micelle formed in self-assembly process, the micelle size and the morphologies were studied. The amphiphilic diblock copolymer have low CMC, indicates its high surface activity. Different oil/water ratio and differerent PHFBMA/PAA molar ratios all can affect the morphology and the size of the aggregates/micelle.