Microwave Accelerated Polymerization of 2‐Phenyl‐5,6‐dihydro‐4H‐1,3‐oxazine: Kinetics and Influence of End‐Groups on Glass Transition Temperature

Summary: The ring‐opening polymerizations of 2‐phenyl‐5,6‐dihydro‐4H‐1,3‐oxazine (PhOZI) with methyl tosylate (MeOTs) and butyl iodide (BuI) as initiators were performed in refluxing butyronitrile. Reaction kinetics under microwave irradiation was compared with conventional oil bath heating. The polymerization rates, under microwave irradiation, showed an acceleration by a factor of 1.8 (independently from the used initiator). The investigation of the thermal properties of the obtained poly(N‐benzoyl‐trimethyleneimine) showed the influence of molecular weight and end‐groups on the glass transition temperature.

The ring‐opening polymerizations of 2‐phenyl‐5,6‐dihydro‐4H‐1,3‐oxazine performed in refluxing butyronitrile.     

Influence of Cyclodextrin and Temperature on the Kinetics of Free Radical Polymerization of N‐Adamantylacrylamide in Water

N‐Adamantylacrylamide ( 3 ) was complexed with randomly methylated β‐cyclodextrin (RAMEB) forming the water‐soluble host–guest monomer‐complex 3a . A 1:1 complex stoichiometry was proven by NMR titration (Job's method). We investigated the free radical polymerization of the complex 3a using the water‐soluble azoinitiator 2,2′‐azobis[2‐(2‐imidazolin‐2‐yl)‐propane]dihydrochloride (VA044) at different temperatures. We observed that, below T_crit a solution polymerization of 3a takes place. Above T_crit, a precipitation mechanism leads to an increase in the relative polymerization rate.

     

Chemoenzymatic Synthesis of Polycaprolactone‐block‐Polystyrene via Macromolecular Chain Transfer Reagents

ε‐Caprolactone (CL) was enzymatically polymerized with 2‐mercaptoethanol as the initiator, both in an oil bath and under microwave (MW) irradiation. The polymerization performed under MW irradiation maintaining equal conditions led to higher yields and less formation of side products, i.e., a higher chemoselectivity was observed. The resulting polyester with a terminal  SH moiety had a of 3 600 g · mol⁻¹, determined by size exclusion chromatography (SEC), and was used as a chain transfer reagent. Subsequent copolymerization with styrene in different ratios led to polycaprolactone‐block‐polystyrene. SEC analysis and polarization microscopy of crystallized samples with different styrene contents proved the formation of block copolymers.

     

Microwave Accelerated Polymerization of 2‐Phenyl‐2‐oxazoline

Summary: We studied the cationic ring‐opening polymerization of 2‐phenyl‐2‐oxazoline under microwave irradiation. A comparison with thermal heating shows a great enhancement in the reaction rates while the living character of the polymerization is conserved. The polymerizations were performed at the temperature of boiling butyronitrile (123 °C). The polymerization of 2‐phenyl‐2‐oxazoline under microwave conditions, described herein for the first time, is shown to be a rapid and environmentally friendly alternative to the classical methods.

Schematic of the activation of the reactive site by microwave irradiation.     

Expanding the hydride chemistry: antiperovskites A3MO4H (A = Rb,Cs; M = Mo,W) introducing the transition oxometalate hydrides

The four compounds A₃MO₄H (A = Rb, Cs; M = Mo, W) are introduced as the first members of the new material class of the transition oxometalate hydrides. The compounds are accessible via a thermal synthesis route with carefully controlled conditions. Their crystal structures were solved by neutron diffraction of the deuterated analogues. Rb₃MoO₄D, Cs₃MoO₄D and Cs₃WO₄D crystallize in the antiperovskite-like K₃SO₄F-structure type, while Rb₃WO₄D adopts a different orthorhombic structure. ²H MAS NMR, Raman spectroscopy and elemental analysis prove the abundance of hydride ions next to oxometalate ions and experimental findings are supported by quantum chemical calculations. The tetragonal phases are direct and wide band gap semiconductors arising from hydride states, whereas Rb₃WO₄H shows a unique, peculiar valence band structure dominated by hydride states.

The synthesis, structures and electronic properties of the first four heteroanionic compounds containing both hydride and transition oxometalate ions are reported.     

Relaxation within the electronic ground state of the ferrous ion in [Fe(H2O)6]K2(SO4)2 single crystals at low temperatures

Single crystal Mössbauer spectra of [Fe(H₂O)₆]K₂(SO₄)₂ taken in external magnetic fields up to 5 T at low temperatures show large line broadenings, which are due to intermediate relaxation rates within the electronic orbital ground state. The spectra are fitted using a Blume stochastic relaxation model, the ferrous ion flipping between two electronic states. The results of the fit are discussed in a ligand field model of the hexaaquo-coordinated high-spin ferrous ion.     

Debye-temperatures and Mössbauer-shift in high-Tc superconductor: Ba2EuCu3O7±δ

The high T_C superconductor Ba₂EuCu_307±δ with measured T_c=94±2 K was investigated by Mössbauer spectroscopy. It is shown that the material at low temperatures has either a very high Debye temperature θ_D > 800 K, or it is crystallographically not single phased with one component (87%) with θ_D = 378±30 K and the other (13%) with θ_D = 136±13 K.     

Evaluation of cracking efficiency of As and P precursors

The cracking behaviour of PH₃, TBP and DitBuPH, AsH₃ and TBAs was studied by mass spectrometry in a production-type MOMBE growth chamber. The measurements were performed varying the cracking temperature of the injector cells and the total material flux. The pyrolysis of the hydrides PH₃/AsH₃ essentially leads to the production of hydrogen and the dimers P₂/As₂. The decomposition of these source materials reaches about 90% at beam pressures in the range of 10⁻⁷ Torr. Under identical conditions TBP, TBAs and DitBuPH are cracked better than 97%. However, the pyrolysis of the alkyl-compounds is accompanied by the formation of isobutene and hydrides. Consequently the decomposition of this PH₃ and AsH₃ produced during cracking is limiting the growth relevant cracking efficiency to the values obtained for the hydrides. The additional occurrence of dihydrides at beam pressures in the range of 10⁻⁵ Torr suggests an initial decomposition process of the source materials via a radical formation mechanism. With respect to the stability of the compounds a self-dissociation of TBAs in the bubbler under the production of isobutane C₄H₁₀ and AsH₃ was detected.