Living/Controlled Radical Polymerization Of Fluoroolefins And Preparation Of Fluorinated Functional Polymers

Since the invention of polytetrafluoroethylene (PTFE) as the world’s first perfluoropolymer by DuPont Company in1938, fluorinated polymers have attracted great attention from scientists of various areas. Due to the high electronegativity of fluorine atom and the strong dissociation energy of C-F bond, fluorinated polymers exhibit many unique and high-performance features, such as chemical interness (to acids, bases and solvents), low refractive indices,low dielectric constants, low dissipation factors,low surface energy, high thermal stability, long durability, hydrophobic and oleophobic properties.Therefore, they have been widely explored and used in many high-technology applications,includingaeronautics, textile finishing, fuel cell membranes, microelectronics, optics,protective coatings, novel elastomers and nuclear industry. As a kind of man-made polymer materials, the evolution of polymerization methods is very important. Since the mid-1990s, several methods of living/controlled radial polymerization have been invented, including nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP), and reversible addition-fragmentation chain transfer (RAFT) polymerization.These methodshave been extensively studied and developed as a useful tool for the synthesis of well-defined polymers with predetermined molecular weights, narrow molecular weight distributions, various topological architecturesand useful end-functionalities. Although these methods have been successfully used in the polymerization of some fluorinated monomers such as fluorinated styrenes, acrylates and methacrylates, living/controlled radical polymerization of fluoroolefins (such as tetrafuoroethylene (TFE), hexafluoropropylene (HFP)and chlorotrifluoroethylene (CTFE)) is still a big challenge, which could be attributed to the gaseous state and the unique chemical properties of fluoroolefins.In this thesis, we systematically investigated the living/controlled radical copolymerization of CFTE or HFP with many other non-fluorinated monomers. Based on this, we have prepared several novel fluorinated polymer materials, including fluorinated polymers containing fluoroalkyl sulfonic acid groups, fluorinated polyurethane and fluorinated film-forming material.The main results of this thesis are listed as follows:1. Considering the relationship between momomer property and chain transfer agent, we designed and synthesized two xanthates (S-benzyl O-ethyldithiocarbonateand ethyl2-(ethoxycarbonothioylthio) acetate,abbreviated to BEDTCand EECTTA, respectively) for the radical copolymerization of HFP and butyl vinyl ether (BVE) under60Co y-ray irradiation at room tempreture. We found that EECTTA has better control effect for the copolymerization with a moderate polymerization rate. The results of kinetic studies and chain extension polymerization indicate that the copolymerization process has the features of living/controlled free radical polymerization. Chemical structures of the obtained copolymers were characterized by1H,19F and13C NMR spectroscopy. The results show that the copolymerization resulted in alternating copolymers. Furthermore, a weak signal ascribed to the quaternary carbon atom of the xanthate groups at the end of the polymer chains can be observed in the13C NMR spectrum, which is another important evidence for the living/controlled character of the polymerization process.The methanol-precipated purified copolymer was further reacted with HFP under60Co y-ray irradiationin order to make the polymers end-capped with HFP units in a higher extent. Then, the resultedend-capped copolymerswere treated with m-chloroperbenzoic acid (m-CPBA) to preparefluorinated polymers containing fluoroalkyl sulfonic acid groups. This is a novel method for preparing fluorosulfuric acid.2. We investigate the radical copolymerization of CTFE and BVE with BEDTC as chain transfer agent and AIBN as initiator at70℃.Results of the kinetic studies and the chain extension polymerization indicate that the copolymerization process has the features of living/controlled free radical polymerization. Chemical structures of the obtained copolymers were characterized by1H,19F and13C NMR spectroscopy. The results show that the copolymerization resulted in alternating copolymers. Furthermore, a weak signal ascribed to the quaternary carbon atom of xanthate groups at the end of the polymer chains can be observed in the13C NMR spectrum, which is another important evidence for the living/controlled character of the polymerization process.However,poly(CTFE-alt-BVE)exhibit very low glass transition temperature (Tg, below0℃), which severely limit their use in usual applications due to the viscous state at ambient temperature.Using the obtained polymer as a macro-CTA, a block copolymer was prepared by chain extension polymerization of vinyl acetate (VAc) and a fluorinated amphiphilic polymerwas obtained via basic methanolisis. After that, we successfully synthesized a novelfluorinated polyurethane with isophorone diisocyanate (IPDI) as the cross-linking agent.This method solves the problem of fairly low Tg value of poly(CTFE-alt-BVE), and makes it suitable for using as protective coating or some other applications.3. We investigate the radical copolymerization of CTFE and N-vinylpyrrolidone(NVP)under60Co γ-ray irradiation at room tempreture with BEDTC as chain transfer agent. NVP is an electron-rich monomer like BVE, which tends to form alternating copolymer with electron-deficient fluoroolefins. However, radical copolymerization of CTFE and NVP didn’t result in perfect alternating copolymer.Molar fractions of CTFE unit in the copolymer increase with the initial molar ratios of CTFE to NVP and the polymerization conversionsaccessed by elemental analysis. Polymerization results reveal that molecular weights of thecopolymers are controlled and the molecular weight distributions are narrow.The results of kinetic studies and chain extension polymerization indicate that the copolymerization process has the features of living/controlled free radical polymerization. Chemical structures of the obtained copolymers were characterized by1H and19FNMR spectroscopy.Moreover, the obtained fluorinated copolymer showed excellent film-forming characteristic, and the physical property of it was preliminarily investigated.4. We investigated the Co(acac)2-mediated radical polymerization of CTFE and VAc. Results of the kinetic studies and the chain extension polymerization indicate that the copolymerization process has the features of living/controlled free radical polymerization. Chemical structures of the obtained copolymers were characterized by1H and19F NMR spectroscopy. Molar fractions of CTFE and NVP units in the resulted copolymer were accessed by elemental analysis. And we found that molar fractions of CTFE unit in the copolymer increase with the initial molar ratios of CTFE to VAc.