Thermal analysis of phenylethynyl end-capped fluorinated imide oligomer afr-pepa-4

Thermal analysis of phenylethynyl end-capped imide oligomer AFR-PEPA-4 was performed to characterize cure reaction, thermal stabilities and semicrystalline behavior of AFR-PEPA-4 oligomer and its cured polyimide. Cured AFR-PEPA-4 polyimide showed high T _gs up to 418°C. Both AFR-PEPA-4 oligomer and polyimide exhibit excellent thermal stabilities comparable to PETI-5 polyimides. AFR-PEPA-4 imide oligomer has a T _m of 330°C and exhibits spherulite crystalline morphology in the film. The crystallinity in AFR-PEPA-4 films could not be regenerated under any annealing conditions after the initial melt.     

The use of bis(diphenylphosphino)amines with N-aryl functionalities in selective ethylene tri- and tetramerisation

A systematic study was conducted on the Cr catalysed tri- and tetramerisation of ethylene using bis(diphenylphosphino)amine ligands with N-aryl functionality. This study revealed that the oligomerisation reaction product selectivity is primarily dependent on the structure and size of the N-aryl groups.

Addition of sufficient steric bulk to the N-phenyl group via ortho-alkyl substitution increased the combined 1-hexene and 1-octene selectivity (overall alpha selectivity) to above 82% at an overall 1-octene selectivity of 56%. The introduction of a single carbon spacer between the N-atom and the aryl-moiety, as well as the addition of branching on this carbon, resulted in further selectivity improvements, achieving an overall 1-octene selectivity of 64% and an overall alpha selectivity of 84%. This was obtained at catalyst productivities in excess of 1,000,000 g/g Cr/h.     

Naphthalene Complexation by β-Cyclodextrin: Influence of Added Short Chain Branched and Linear Alcohols

Naphthalene forms 1 : 1 complexes with -cyclodextrin (-CD)in water. The binding constant is 377 ± 35 M^-1. Addition of linear or branched alcohols causes a reduction in the apparent strength of naphthalene binding (K_app) compared to the value in the absence of additives. For example, 1% 1-pentanol reduces K_app to 184 ± 31 M^-1. Branching does not alter K_app much for a given number of carbon atoms, e.g., it is 113 ± 9 M^-1for 2-pentanol and 116 ± 8 M^-1for 3-pentanol. The exception to this is tert-butanol for which K_app is 577 ± 40 M^-1. The variation in K_app as a function of [1-pentanol] yields values for the individual equilibrium constants contributing to K_app. This reveals that a ternary complex forms involving naphthalene, the CD and 1-pentanol. The constant for formation of the ternary complex is 99 ± 29 M^-2. NaI quenching of naphthalene fluorescence indicates that the CD cavity partially protects the naphthalene excited state fromthis water phase quencher. Interestingly, the Stern–Volmer constant is lower in the presence of 1-pentanol than in its absence, although there should be more unbound (and therefore more NaI accessible) naphthalene in the former system than in the latter. These apparently contradictory results are discussed in terms of ternary complex formation.     

On the formation of artefact peaks in linked scans of the magnet and electric sector fields in a mass spectrometer

The apperrance of peaks at non-integral masses in linked scans, where the ratio B/E is kept constant, is shown to be caused by fragmentations of metastable ions occuring in the region between the magnetic and electric sectors. A formula is given for calculating the mass of the parent metastable ion and that of its daughter ion.     

Electron-impact fragmentation of penta-fluorophenyldimethylsilyl ethers of some sterols of biological importance

The mass spectral properties under medium and high resolution of a new protecting group for sterols is described and its ability to direct fragmentation is compared with established derivatives. The mass spectra obtained are characterised by strong molecular ions which fragment to produce a more even ion distribution than the familiar TMS ethers. This results in enhanced abundance of hydrocarbon fragments, with molecular structural details given greater prominence than is found with other derivatives.