A Study On Synthesis Of Fluorine-containing Monomers

Fluorine-containing materials have excellent thermal and chemical stability, surface and optical properties due to the special characteristics of fluorine such as the greatest electronegativity among all elements, very small atom radius, short and strong C-F bond and so on. Based on these characteristics of fluorine, a series of monomers such as fluorine-containing styrenes and tris(3,5-difluorophenyl)methyl methacrylate (3,5-F₆TrMA ) were prepared in this paper.In the attempt to avoid the shortage of brittleness of perfluorinated polymers and improve their process ability and resolvability while maitaining their good performances, we therefore synthesized a series of partial fluorinated styrenes: m-trifluoromethylstyrene, 3,5-bis(trifluoromethyl)styrene and pentafluorostyrene. These fluorine-containing styrenes were obtained through bromination, Grignard reaction, reduction and dehydrolyzation in overall yields of 52.5%⁶2.5% from the corresponding basic materials trifluoromethylbenzene, 1,3-bis(trifluoromethyl)benzene and pentafluorobenzene (decarboxylated from pentafluorobenzoic acid in advance). This method hasn't been reported. The bromination of corresponding deactivated aromatics was also studied in this paper.In the end of 1970s Japanese scientists synthesized an optically active polymer—poly(triphenylmethyl methacrylate) (PTrMA), which was used in the chiral stationary phase for high-performance liquid chromatography (HPLC) for resolving various enantiomers. But PTrMA easily loses its optical activity by solvolysis when methanol is used as an eluent. It is found that methanolysis is accelerated by the electro-donating substituents and slowed down by the electro-withdrawing subsituents on the phenyl rings. In order to improve the durability of PTrMA to methanolysis, we make the use of the greatest eletronegativity of fluorine synthesizing tris(3,5-difluorophenyl)methyl methacrylate on which has 3-, 5- fluorine substituents. 3,5-F₆TrMA was prepared from 1-bromo-3,5-difluorobenzene with two methods. In method one, the product was synthesized through Grignard reaction, reacation with CO₂, esterification, additive reaction, chloridization, esterification respectively in an overall yield of 45.2%; in method two, the product was obtained through Grignard reaction, additive reaction, esterification in yield of 74%, all the processes were carried out in one"pot"without treatment until the last reaction, and this method hasn't been reported. Tris(3,5-difluorophenyl)methyl Chloride and tris(3,5-difluorophenyl)methyl methacrylate are new chemicals haven't been reported either. Their structures are confirmed by IR, ¹HNMR, ¹³CNMR and MS. The 3,5-F₆TrMA was found to be extraordinarily durable to methanolysis after the test. It hasn't started decomposition yet by methanol during a long time of 6 months, while the most durable monomer previously reported was tris(3,4-difluorophenyl)methyl methacrylate, its half-life time was 1920 minutes. Asymmetric polymerization of 3,5-F₆TrMA was also studied, but due to the rigid conditions, only the oligomers having specific rotation of 4.5°were obtained. The mechanism of methanolysis of TrMA was also studied based on the stability of triaryl carbocations.