8 research outputs found
Electrostatic trapping of metastable NH molecules
We report on the Stark deceleration and electrostatic trapping of NH
() radicals. In the trap, the molecules are excited on the
spin-forbidden transition and detected via
their subsequent fluorescence to the ground state. The 1/e
trapping time is 1.4 0.1 s, from which a lower limit of 2.7 s for the
radiative lifetime of the state is deduced. The spectral
profile of the molecules in the trapping field is measured to probe their
spatial distribution. Electrostatic trapping of metastable NH followed by
optical pumping of the trapped molecules to the electronic ground state is an
important step towards accumulation of these radicals in a magnetic trap.Comment: replaced with final version, added journal referenc
Acid-Labile Surfactants Based on Poly(ethylene glycol), Carbon Dioxide and Propylene Oxide: Miniemulsion Polymerization and Degradation Studies
Partially degradable, nonionic AB and ABA type di- and triblock copolymers based on poly(propylene carbonate) and poly(ethylene glycol) blocks were synthesized via immortal copolymerization of carbon dioxide and propylene oxide, using mPEG or PEG as a macroinitiator, and (R,R)-(salcy)-CoOBzF5 as a catalyst in a solvent-free one-pot procedure. The amphiphilic surfactants were prepared with molecular weights (Mn) between 2800 and 10,000 g·mol−1 with narrow molecular weight distributions (1.03–1.09). The copolymers were characterized using 1H-, 13C- and DOSY-NMR spectroscopy and size exclusion chromatography (SEC). Surface-active properties were determined by surface tension measurements (critical micelle concentration, CMC; CMC range: 1–14 mg·mL−1). Degradation of the acid-labile polycarbonate blocks was investigated in aqueous solution using online 1H-NMR spectroscopy and SEC. The amphiphilic polymers were used as surfactants in a direct miniemulsion polymerization for poly(styrene) (PS) nanoparticles with mean diameter of 270 to 940 nm. The usage of an acid-triggered precipitation of the emulsion simplified the separation of the particles from the surfactant and purification of the nanoparticles
Rigid Hyperbranched Polycarbonate Polyols from CO<sub>2</sub> and Cyclohexene-Based Epoxides
Hyperbranched,
multifunctional polycarbonate polyols based on CO<sub>2</sub>, cyclohexene
oxide (CHO), and the “inimer”
(initiator–monomer) (4-hydroxymethyl)cyclohexene oxide
(HCHO) were prepared in one-pot syntheses. The related linear poly(hydroxymethyl
cyclohexene carbonate) structures based on protected HCHO and postpolymerization
deprotection were also synthesized as model compounds. The content
of hydroxyl functionalities was adjustable for both linear and hyperbranched
terpolymer systems. All CO<sub>2</sub>/epoxide polymerizations were
catalyzed by the (<i>R</i>,<i>R</i>)-(salcy)-Co(III)Cl
complex. The polycarbonates obtained were comprehensively investigated
using various 1D and 2D NMR techniques, SEC, FT-IR, UV–vis
spectroscopy, and contact angle measurements. Rigid polyols with molecular
weights between 3600 and 9200 g mol<sup>–1</sup> and moderate
dispersity between 1.18 and 1.64 (<i>M</i><sub>w</sub>/<i>M</i><sub>n</sub>) were obtained. In addition, the materials
were examined with respect to their thermal properties, intrinsic
viscosity, and their three-dimensional structure. Glass transition
temperatures in the range of 113–141 °C (linear) and 72–105
°C (hyperbranched) were observed. The intrinsic viscosity of
the hyperbranched systems is in the range of 5.69–11.51 cm<sup>3</sup> g<sup>–1</sup> and mirrors their compact structure.
The hyperbranched polyols were also studied regarding their successful
reaction with phenyl isocyanate to convert the free hydroxyl groups
into urethanes
Multiarm Polycarbonate Star Polymers with a Hyperbranched Polyether Core from CO<sub>2</sub> and Common Epoxides
Multiarm star copolymers, consisting
of hyperbranched poly(ethylene
oxide) (<i>hb</i>PEO) or poly(butylene oxide) (<i>hb</i>PBO) polyether copolymers with glycerol branching points as a core,
and linear aliphatic polycarbonate arms generated from carbon dioxide
(CO<sub>2</sub>) and epoxide monomers, were synthesized via a “core-first”
approach in two steps. First, hyperbranched polyether polyols were
prepared by anionic copolymerization of ethylene oxide or 1,2-butylene
oxide with 8–35% glycidol with molecular weights between 800
and 389,000 g·mol<sup>–1</sup>. Second, multiple arms
were grown via immortal copolymerization of CO<sub>2</sub> with propylene
oxide or 1,2-butylene oxide using the polyether polyols as macroinitiators
and (<i>R</i>,<i>R</i>)-(salcy)-CoCl as a catalyst
in a solvent-free procedure. Molecular weights up to 812,000 g·mol<sup>–1</sup> were obtained for the resulting multiarm polycarbonates,
determined by online viscometry with universal calibration and <sup>1</sup>H NMR. Comparing the synthesis of different multiarm star
polycarbonates, a combination of a highly reactive macroinitiator
with a less reactive epoxide monomer was found to be most suitable
to obtain well-defined structures containing up to 88 mol% polycarbonate.
The multiarm star copolymers were investigated with respect to their
thermal properties, intrinsic viscosity, and potential application
as polyols for polyurethane synthesis. Glass transition temperatures
in the range from −41 to +25 °C were observed. The intrinsic
viscosity could be adjusted between 5.4 and 17.3 cm<sup>3</sup>·g<sup>–1</sup> by varying the ratio of polyether units and polycarbonate
units