2D-NMR studies of a model for Krytox® fluoropolymers.

Multiple two-dimensional nuclear magnetic resonance (2D-NMR) techniques have been used to study the structures of Krytox(®) perfluoro(polyalkyl ether) and its mechanism of polymerization. Model compound K(4), containing four Krytox(®) fluoropolymer repeat units, was analyzed to interpret the multiplet patterns in the NMR spectra from the polymer model. (19)F {(13)C}-Heteronuclear single-quantum correlation experiments, performed with delays optimized for (1)J(CF) and (2)J(CF), provided spectra that permitted identification of resonances from individual monomer units. Selective, (19)F-(19)F COSY 2D-NMR experiments were performed with different excitation regions; these experiments were combined with selective inversion pulses to remove (19)F-(19)F J couplings in the f(1) dimension. The resulting COSY spectra were greatly simplified compared with standard (19)F-(19)F COSY spectra, which are too complicated to interpret. They give information regarding the attachments of monomer units and also provide insights into the nature of the stereoisomers that might be present in the polymer. Both infrared and NMR spectra show peaks identifying chain end structures. With the help of these studies, resonances can be assigned, and the average number of repeat units in the polymer chain can be calculated based on the assignments obtained.

Ultrafast synthesis of ultrahigh molar mass polymers by metal-catalyzed living radical polymerization of acrylates, methacrylates, and vinyl chloride mediated by SET at 25 degrees C.

Conventional metal-catalyzed organic radical reactions and living radical polymerizations (LRP) performed in nonpolar solvents, including atom-transfer radical polymerization (ATRP), proceed by an inner-sphere electron-transfer mechanism. One catalytic system frequently used in these polymerizations is based on Cu(I)X species and N-containing ligands. Here, it is reported that polar solvents such as H(2)O, alcohols, dipolar aprotic solvents, ethylene and propylene carbonate, and ionic liquids instantaneously disproportionate Cu(I)X into Cu(0) and Cu(II)X(2) species in the presence of a diversity of N-containing ligands. This disproportionation facilitates an ultrafast LRP in which the free radicals are generated by the nascent and extremely reactive Cu(0) atomic species, while their deactivation is mediated by the nascent Cu(II)X(2) species. Both steps proceed by a low activation energy outer-sphere single-electron-transfer (SET) mechanism. The resulting SET-LRP process is activated by a catalytic amount of the electron-donor Cu(0), Cu(2)Se, Cu(2)Te, Cu(2)S, or Cu(2)O species, not by Cu(I)X. This process provides, at room temperature and below, an ultrafast synthesis of ultrahigh molecular weight polymers from functional monomers containing electron-withdrawing groups such as acrylates, methacrylates, and vinyl chloride, initiated with alkyl halides, sulfonyl halides, and N-halides.

A suite of 3D NMR methods for characterizing complex hydrocarbon structure fragments.

A suite of triple resonance 3D NMR experiments is presented for the complete connectivity assignment of the hydrocarbon network in complex macromolecular and supramolecular organic structures. These new 3D NMR methods rely only on the presence of a unique set of (13)C resonances (from (13)C(X)) which are separated from the rest of the (13)C NMR spectrum. These experiments take the advantage of region selective excitation and selective inversion by composite pulses to provide correlations among H(A), (13)C(A); H(B), (13)C(B) and neighboring (13)C(X) resonances along three frequency dimensions. These methods include: gHC(A)C(X), gHC(A)C(X)-HH-TOCSY and gHC(A)C(X)-CC-TOCSY experiments. The utility of this approach is illustrated with spectra of selected structure fragments in poly(ethylene-co-n-butyl acrylate-co-carbon monoxide) (polyEBC) prepared from 1,2,3-(13)C(3)-n-butyl acrylate.