Solid-state topochemical polymerization is one way to synthesize novel macromolecular architectures with stereoregular chain structures. Topochemical reactions are attractive, ''green'' synthetic pathways in material design, since they occur in solvent-free conditions and in response to external stimuli, such as heat and light. For the first time, we have used the reversible [2p + 2p]-cycloaddition of a bioinspired bis-thymine monomer to topochemically synthesize a polymer. The polymer can be fully photodepolymerized to the monomer and then reversibly and repeatedly photo-polymerized and photodepolymerized. This is the first demonstration of complete photo-depolymerization and subsequent monomer recycling using this mechanism.
An RF-only quadruple collision cell, fitted with retardation and acceleration lenses, has been installed in a field-free region of a large-scale tandem mass spectrometer. This new arrangement has allowed decelerated, mass-selected ions (ca. 5 eV kinetic energy) to react with reagent gases and reaccelerated, mass-selected products (cu. 8 keV) to be subsequently identified by collisional activation mass spectrometry. The system was tested by looking at ion/molecule reactions of cyelobutanone molecular ions, previously studied by FTICR mass spectrometry Collisional activation (CA) mass spectrometry is a well-established technique for the characterization of fast-ion beams.' Isomeric ions are usually clearly distinguished because the technique provides not only fingerprint spectra of isomers, but also direct structural information, since simple, site-specific cleavages are frequently induced. CA mass spectrometry has more recently been implemented as the powerful neutralization-reionization (NR) technique' which, due to a higher energy deposition in the ions,3 gives rise to spectra which are even more structurally significant.In some instances, however, the interpretation of CA spectra is not straightforward and a further stage of mass spectrometric analysis, i.e. an MS/MS/MS (MS3) experiment is then r e q~i r e d .~ In these experiments, collision-induced fragments are mass-selected and subjected to a further collisional activation step. It must be recognized that such experiments may just displace the initial problem and other kinds of information are therefore required. The occurrence of post-collisional isomerization of ions may also introduce ambiguities; such processes have been reported recently for some sulfur-containing organic ions.The reactivity of ions towards neutral reagents provides another method for isomer differentiation. Such reactions are most easily performed in a chemical ionization (CI) source and, if the source is installed on a sector instrument, mass-selected products can be identified by high-energy collisional activation.6 It is, however, often difficult to identify unambiguously the reaction which leads to a specific product, since different ions and neutrals are present at the same time. This difficulty can be overcome by the use of Fourier-transform ion cyclotron resonance (FTICR) methodology which allows mass-selected ions to be collisionally stabilized, to react with appropriate reagents or to be collisionally dec~mposed.~ Note, however, that fragmentation of these precursor ions takes place at low kinetic energy.Other recent instrumentation allowing inter uliu the study of ion/molecule reactions has been recently reviewed by Cooks et aL8 Among the different approaches, results obtained by these authors using a home-built pentaquadrupole instrument appear quite Authors for correspondence promi~ing.~ Again, collision-induced dissociations of the ion/molecule products are obtained in the low kinetic energy regime.We describe in this paper the modification of a large sector mass spectrom...
Atmospheric pressure chemical ionization (negative ion) and electrospray ionization (positive and negative ion) mass spectrometry and nuclear magnetic resonance ( 1 H NMR and 13 C NMR) were used to characterize the prepolymer (i.e.
uncrosslinked) poly(xylitol sebacate) (PXS), prepared by condensation of xylitol [X] and sebacic acid [S], and this was compared with poly(glycerol sebacate) (PGS), prepared by condensation of glycerol [G] and [S]. The PXS prepolymer, prepared at 118 ∘ C/24 h, gave predominantly 1-acyl-[XS] and 1,5-diacyl-[SXS] species and smaller amounts of 2-acyl substitutions. At 130 ∘ C/24 h an increase of the amount of the 1-acyl and 1,5-diacyl substitutions in the [(SX) n ], [S(XS) n ] and [(XS) n X] series was identified, as was found for the analogous PGS prepolymer ([(SG) n ], [S(GS) n ] and [(GS) n G] series). Novel tetrahydrofuranyl species were found in the PXS prepolymer. Further polymerization of the PXS prepolymer gave a gel which when analysed using 13 C NMR was shown to mainly contain 1-acyl and 1,5-diacyl substitutions.
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