Random Copolymers of 1,5-Dioxepan-2-one

ABSTRACT

Copolymers of 1,5-dioxepan-2-one (DXO) and e-caprolactone (?-CL), δ-valerolactone (δ-VL) or L-lactide (LLA) have been synthesized and characterized. High molecular weight copolymers were obtained using stannous-2-ethyl hexanoate as catalyst in bulk. Reactivity ratios for the copolymerization of DXO and δ-VL were determined at 110°C as r_VL=0.5 and r_DXO=2.3. At high conversion, depolymerization of δ-VL occurred, resulting in lower molecular weight and variations in the copolymer composition.

Physical properties, such as crystallinity and melting temperature of the DXO-copolymers proved to be strongly dependent on the choice of comonomer and on the molar composition of the copolymers. DXO appears to be incorporated into the poly-?-caprolactone (PCL) crystals and to some extent into the poly-δ-valerolactone (PVL) crystals, resulting in a more gradual decrease in crystallinity with increasing amount of DXO.     

Secondary ion yields produced by keV atomic and polyatomic ion impacts on a self-assembled monolayer surface

A suite of keV polyatomic or 'cluster' projectiles was used to bombard unoxidized and oxidized self-assembled monolayer surfaces. Negative secondary ion yields, collected at the limit of single ion impacts, were measured and compared for both molecular and fragment ions. In contrast to targets that are orders of magnitude thicker than the penetration range of the primary ions, secondary ion yields from polyatomic projectile impacts on self-assembled monolayers show little to no enhancement when compared with monatomic projectiles at the same velocity. This unusual trend is most likely due to the structural arrangement and bonding characteristics of the monolayer molecules with the Au(111). Copyright 1999 John Wiley & Sons, Ltd.     

Fusion around the barrier for 7Li+12C

Fusion cross-sections for the ⁷Li + ¹²C reaction have been measured at energies above the Coulomb barrier by the direct detection of evaporation residues. The heavy evaporation residues with energies below 3 MeV could not be separated out from the α-particles in the spectrum and hence their contribution was estimated using statistical model calculations. The present work indicates that suppression of fusion cross-sections due to the breakup of ⁷Li may not be significant for ⁷Li + ¹²C reaction at energies around the barrier.     

Burial effects of organic coatings on the heterogeneous reactivity of particle-borne benzo[a]pyrene (BaP) toward ozone

With an aerosol flow tube coupled to an Aerodyne aerosol mass spectrometer (AMS), room temperature (296 ± 3 K) kinetics studies have been performed on the reaction of gas-phase ozone with benzo[a]pyrene (BaP) adsorbed in submonolayer amounts to dry ammonium sulfate (AS) particles. Three organic substances, i.e., bis(2-ethylhexyl)sebacate (BES, liquid), phenylsiloxane oil (PSO, liquid), and eicosane (EC, solid), were used to coat BaP-AS particles to investigate the effects of such organic coatings on the heterogeneous reactivity of PAHs toward ozone. All the reactions of particle-borne BaP with excess ozone exhibit pseudo-first-order kinetics in terms of BaP loss, and reactions with a liquid organic coating proceed by the Langmuir-Hinshelwood (L-H) mechanism. Liquid organic coatings did not significantly affect the kinetics, consistent with the ability of reactants to rapidly diffuse through the organic coating. In contrast, the heterogeneous reactivity of BaP was reduced substantially by a thin (4-8 nm), solid EC coating and entirely suppressed by thick (10-80 nm) coatings, presumably because of slow diffusion through the organic layer. Although the heterogeneous reactivity of surface-bound PAHs is extremely rapid in the atmosphere, this work is the first to experimentally demonstrate a mechanism by which the lifetime of PAHs may be significantly prolonged, permitting them to undergo long-range transport to remote locations.     

Real meromorphic functions and linear differential polynomials

We determine all real meromorphic functions f in the plane such that f has finitely many zeros, the poles of f have bounded multiplicities, and f and F have finitely many non-real zeros, where F is a linear differential polynomial given by F = f (k) +Σk-1j=0ajf(j) , in which k≥2 and the coefficients aj are real numbers with a0≠0.     

Studies in neutron depth profiling

This paper describes first the application of neutron depth profiling (NDP) for measuring the distribution of⁶Li in LiAlO₂ ceramics. Using a surface barrier detector for detecting³H produced in⁶Li(n, )³H,⁶Li was profiled to a depth of 14 m in the ceramics. Secondly, a new methodology is presented for NDP with enhanced capabilities based on measuring the energy of recoiling nuclei from (n, p) and (n, ) reactions by time-of-flight mass spectrometry. The scope of recoil nucleus time-of-flight mass spectrometry (RN-TOF-MS) includes profiling of¹⁰B,¹⁴N,¹⁷O,³³S,³⁵Cl,⁴⁰K. Probe depths may be of a few tens nanometers. RN-TOF-MS complements and refines NDP based on charged particle (p or ) spectrometry.     

Sorption of inorganic nanoparticles in woven cellulose fabrics

Titanium dioxide was deposited from aqueous suspension onto cellulosic surfaces.Titania was sourced from Degussa (P25TM,70:30 anatase:rutile).Dry uptake of particles was shown to be rapid and dominant with one-third of the deposition occurring in less than 30 s and over one-half in the first minute.Isotherms were recorded to compare the rate of titanium deposition on dry and pre-wetted cotton.In the dry case uptake reached a maximum in 30 min whereas in the pre-wetted case the uptake was seen to continue beyond 180 min.A broad trend of higher deposition occurring at lower pH was seen,corresponding to the region where surface charges were opposite and thus attractive.Dry pickup was less significant at high pH.The response to varying ionic strength was complex and was attributed to the combined effect of charge screening,particle aggregation and consequent particle entrapment or occlusion.Titania deposition into the interstices of woven cotton sheets resulted in the formation of inorganic,nanoparticulate skeletons which could be isolated by controlled combustion of the cellulose and thus cotton was suggested to have potential for the templated synthesis of high surface area semiconductor materials.     

Syntheses and reactions of some fluorinated dienes,cyclobutenes and furans

There are many reports¹ of the pyrolysis of fluorinated organic compounds, including the defluorination of cyclic fluorocarbons over iron to give aromatic compounds. Extending this technique we have investigated the flow pyrolysis of some readily accessible unsaturated fluorocarbons, such as I, II, and III, and found these to be synthetically

useful routes to fluorinated dienes, cyclobutenes, and furans. Pyrolyses were carried out using a nitrogen flow over platinum, iron or caesium fluoride heated at 430–700°. The various products can all be rationalized in terms of intermediate allylic radicals, and the solid substrate influences which allylic radicals are formed.We are also investigating the chemistry of those now accessible compounds, such as IV, V, and VI, and some of the preliminary results are described.

For example the fluoride ion induced dimerisation of IV gave two major products VII and VIII via a particular interesting mechanism.