The synthesis and the characterization of fluoroelastomers, based on vinylidene fluoride (VDF) and perfluoromethyl vinyl ether (PMVE), poly(VDF-co-PMVE) copolymers, by iodine transfer copolymerization are presented. These statistic poly(VDF-co-PMVE) copolymers were prepared in the presence of a perfluoromonoiodo functional chain transfer agent (CTA), C6F13I, or telechelic diiodoperfluoroalkane CTAs, IC6F12I and IC4F8I, using an emulsion process without any surfactant. Quasi-optimal conditions were found to lead to poly(VDF-co-PMVE) copolymers in satisfactory yields. The copolymer compositions, the molecular weights, and end-groups of these random-type copolymers were assessed by means of 19F NMR spectroscopy. Model molecules containing only one PMVE unit were synthesized by the radical addition of different CTAs (ICl, ICF2I, CF3I) onto PMVE to help in the assignments by 19F NMR spectroscopy of the characteristic signals of the end-group, i.e., −CF2CF(OCF3)I and −CF(OCF3)CF2I. Indeed, only −CH2CF2−I (major amount) and −CF2CH2−I end-groups of these poly(VDF-co-PMVE) copolymers were noted, showing the high reactivity of PMVE−I in the iodine transfer polymerization of VDF. The CTA concentration enabled one to control the molecular weights of the resulting telechelic diiodopoly(VDF-co-PMVE) copolymers ranging from 1000 to 18 000 g mol−1 (assessed by 19F NMR), produced for the first time. It was also noted that the higher the molar masses, the higher the amount of −CF2CH2−I end-group. The controlled behavior of that polymerization was also evidenced by the absence of the reversed −CH2CF2−CF2CH2− VDF dyads, narrow polydispersity indices (<1.75), and the linear “molar mass versus monomer conversions” relationship. Finally, the thermal properties, i.e., the glass transition temperatures (T g) and degradation temperatures, of these copolymers were assessed and were found to depend on the molecular weights and on the monomer composition of the copolymers. These fluoroelastomers had T gs ranging from −63 to −35 °C according to their molecular weights and the contents of both comonomers, with decomposition temperatures greater than 250 °C under air.

A new perfluorocarbon, PTBD (perfluoro-2,2,2',2'-tetramethyl-4,4'-bis(1,3-dioxolane)), is described for use in 19F MR imaging and spectroscopy. Two-thirds of the molecular fluorine in PTBD resonates at a single frequency and can be imaged without the use of frequency-selective spin-echo (SE) MRI pulse sequences to suppress chemical shift artifacts. The absence of strong homonuclear spin-spin coupling to the imagable -CF3 groups in PTBD minimizes signal attenuation in 19F SE MRI due to J-modulation effects. For equimolar concentrations of perfluorocarbon, PTBD gives an approximately 17% increase in sensitivity, relative to literature results for perfluorinated amines, at short values of TE (approximately 10 ms) in 19F SE MRI. These attributes allow 19F MRI of PTBD to be performed on standard clinical imaging instrumentation (without special hardware and/or software modification) and an in vivo example in a mouse is shown. This investigation involved characterizing the MR T1 and T2 relaxation times of PTBD as well as the MR spin-lattice relaxation rate, R1 (1/T1), of PTBD as a function of dissolved oxygen concentration. The T1 and T2 relaxation times and R1 relaxation rates of perfluorooctyl bromide (PFOB) were also obtained, under similar experimental conditions, to compare and contrast PTBD with a representative perfluorocarbon that has been widely employed for 19F MRI/MRS applications.

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Guanine reacts with several benzenediazonium ions rapidly in aqueous solution at pH 10.5 to form 8-(arylazo)guanines in good yield. The reaction of guanine with 4-bromobenzenediazonium ion forms 8-[(4-bromophenyl)azo]guanine about 50-fold more rapidly than the reaction of adenine with this ion to yield 6-[3-(4bromophenyl)-2-triazen-l-yl]purine under these experimental conditions. Guanosine reacts much more slowly than guanine with the benzenediazonium ions in aqueous solution at pH 8.5 or 10.5 to give 8-arylguanosines. The structures of these products were established by their spectroscopic properties and by their quantitative conversion to 8-arylguanines. 5'-Guanylic acid also reacts quite slowly with the benzenediazonium ions in aquous solution at pH 10.5. Only the compounds with strong electron-withdrawing groups yield N-2 triazenes at ambient temperature. No 8-aryl or 8-ary lazo compounds are formed with 5'-guanylic acid at this temperature. However, 4-bromoand 4-sulfobenzenediazonium ions react with 5'-guanylic acid at higher temperatures to yield the 8-aryl-5'-guanylic acids in low yield. The structures of these products were proven by hydrolysis to 8-arylguanines. The 8-arylguanosines and the 8-aryl-5'-guanylic acids are formed via free-radical phenylation reactions. The factors governing the reactivity of the adenines and the guanines are discussed.

Teflon® AF, a family of copolymers of perfluoro‐2,2‐dimethyldioxole with tetrafluoroethylene, and Cytop®, a ring‐cyclized homopolymer of CF2=CFO(CF2)2CF=CF2 are the first commercial amorphous perfluoroplastics which combine high optical clarity and solubility with outstanding chemical, thermal and electrical properties. The processes for making these materials are described and recent structure‐property studies that reveal dramatic substituent effects on polymer Tg and related properties are reviewed. The results of some initial fundamental kinetic studies on fluorinated free‐radical cyclizations that relate to efficient cyclopolymerization of fluorinated dienes and the design of new ring‐containing fluoroplastics are discussed.

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