Thermal and photo-degradation of unstabilized ABS

Thermal- and photo-stabilities of unstabilized acrylonitrile-butadiene-styrene terpolymer, ABS, have been investigated by i.r. spectroscopy. Degradation of ABS samples is initiated by attack on the polybutadiene (PB) component; oxidation products containing hydroxyl and carbonyl groups are produced. The effect of prior thermal processing is to introduce into the polymer hydroperoxides arising from oxidative destruction of PB-unsaturation; these hydroperoxides act as catalysts during subsequent u.v. irradiation. The insolubility of degraded samples of ABS is associated with the formation of cross-linked structures and occurs mainly in the PB segment. It is concluded that the degradation characteristics of ABS are essentially those of the polybutadiene component.     

Quinoline Functionalized Schiff Base Silver (I) Complexes: Interactions with Biomolecules and In Vitro Cytotoxicity,Antioxidant and Antimicrobial Activities

A series of fifteen silver (I) quinoline complexes Q1–Q15 have been synthesized and studied for their biological activities. Q1–Q15 were synthesized from the reactions of quinolinyl Schiff base derivatives L1–L5 (obtained by condensing 2-quinolinecarboxaldehyde with various aniline derivatives) with AgNO₃, AgClO₄ and AgCF₃SO₃. Q1–Q15 were characterized by various spectroscopic techniques and the structures of [Ag(L1)₂]NO₃ Q1, [Ag(L1)₂]ClO₄ Q6, [Ag(L2)₂]ClO₄ Q7, [Ag(L2)₂]CF₃SO₃ Q12 and [Ag(L4)₂]CF₃SO₃ Q14 were unequivocally determined by single crystal X-ray diffraction analysis. In vitro antimicrobial tests against Gram-positive and Gram-negative bacteria revealed the influence of structure and anion on the complexes′ moderate to excellent antibacterial activity. In vitro antioxidant activities of the complexes showed their good radical scavenging activity in ferric reducing antioxidant power (FRAP). Complexes with the fluorine substituent or the thiophene or benzothiazole moieties are more potent with IC₅₀ between 0.95 and 2.22 mg/mL than the standard used, ascorbic acid (2.68 mg/mL). The compounds showed a strong binding affinity with calf thymus-DNA via an intercalation mode and protein through a static quenching mechanism. Cytotoxicity activity was examined against three carcinoma cell lines (HELA, MDA-MB231, and SHSY5Y). [Ag(L2)₂]ClO₄ Q7 with a benzothiazole moiety and [Ag(L4)₂]ClO₄ Q9 with a methyl substituent had excellent cytotoxicity against HELA cells.     

Natural weathering,photo- and thermal oxidation of the two-phase system polyisobutylene and poly(methyl methacrylate)

Blends of polyisobutylene (PIB) and poly(methyl methacrylate) (PMMA) covering the entire composition range have been examined by subjecting them to natural weathering, thermal oxidation and photoxidation. By i.r. analysis, viscometry and Instron testing, interaction between the two polymers was discovered. The blend of 20:80 PIB-PMMA gave the best mechanical performance. I.R. analysis indicated that the degradation of the blends led to enhancement of the interaction between the two polymers giving the blends improved resistance against oxidation. The blend of 20:80 PIB-PMMA proved to be the most stable against heat and light. PIB and PMMA degrade by a chain scission mechanism as indicated by changes in molecular weight.     

Centimeter and millimeter wave attenuation by atmospheric gases and rainfall at a tropical station

The radiowave attenuation due to oxygen and water vapour has been computed over the frequency range 3–350 GHz making use of the mean surface air pressure, temperature and water vapour at Ile-Ife (geog. lat 7.5°N, long 4.5°E) in Southern Nigeria. It is observed that the attenuation at this tropical location is generally higher than at temperate climates. A similar analysis was performed for rainfall attenuation using rainfall intensity measurements. The results obtained with three different expressions for the rain height showed that a rain height of 3 km is a reasonable assumption for estimating earth-space rainfall attenuation at this location. It is found that for frequencies above 200 GHz, the polarization dependence of the specific attenuation due to rainfal becomes negligible. The computed attenuation is lower that that predicted using the corresponding CCIR rain climate data. The results show that whilst the contribution of oxygen and water vapour to the total atmospheric attenuation could be neglected when compared with rainfall attenuation up to about 150 GHz, the contribution becomes significant for frequencies above 190 GHz.     

trans‐Bis­[2,3‐di­amino‐(R,S)‐propion­ato‐N,N′]­di­aqua­copper(II) dihydrate

The title copper complex, [Cu(dl ‐DAP)₂(H₂O)₂]·2H₂O or [Cu(C₃H₇N₂O₂)₂(H₂O)₂]·2H₂O, prepared from the non‐protein amino acid dl ‐2,3‐di­amino­propionic acid (dl ‐HDAP), has a center of symmetry and a distorted octahedral coordination, with four N atoms in equatorial positions and two water mol­ecules in apical sites. The water mol­ecule of crystallization is hydrogen bonded to the deprotonated carboxyl­ate group of the ligand.     

A single-source route to CdS nanorods

We report the preparation of CdS nanorods using a thiosemicarbazide complex of cadmium [Cd(NH2CSNHNH2)2Cl2]. The precursor was decomposed in tri-n-octylphosphine oxide (TOPO) at 280 degrees C to give TOPO capped CdS nanoparticles; nano-dimensional rods of the material are clearly visible in transmission electron microscopy (TEM); the particles have been further characterised by X-ray diffraction (XRD) and selected area electron diffraction (SAED) and optical measurements.     

Interaction of divalent ions of copper,magnesium and zinc with isotactic polymethacrylic acid

The interaction of divalent metal ions (Cu²⁺, Mg²⁺ and Zn²⁺) with isotactic poly(methacrylic acid) (PMAA) has been studied using potentiometric, equilibrium dialysis and viscometric techniques. Partially neutralized isotactic PMAA was titrated with solutions of metal ion so as to enable the polymer/metal ion ratio to be varied over a wide range. The results show the existence of two types of complexes, one at low and the other at high metal ion concentrations. Results from dialysis studies confirm the observations from potentiometric results, indicating the existence of two types of complexes in the solution. Viscometric titrations reveal that the presence of the bound metal ions on the polyelectrolyte imposes structural restrictions on the chain.     

Binding of Cu(II) to poly(methacrylic acid)

The binding of Cu(II) ions to partly neutralized poly(methacrylic acid) (PMA) has been investigated by potentiometric titration and dialysis to determine the stoichiometry the Cu–PMA complexes formed. Partly ionized PMA was titrated with solutions of the metal ion to enable a large range of metal ion/polymer ratios to be studied. Combination of the results from these two techniques at ionic strength 0.1 indicates that at very low Cu(II)/polymer ratios, a 4:1 complex exists, but at higher ratios the complex breaks down to give a mainly 2:1 coordination with some 1:1 binding. Conductance titrations support these results. Viscometric titrations show strong interactions between the metal and polymer, preventing the full extension of the polyion at high degrees of ionization, and spectrophotometric titrations support the existence of at least two types of complexes in the solution.     

The effect of 3,5-ditert.butyl-4-hydroxybenzylthioglycollate and tinuvin P on the thermal,photo and natural degradation of ABS

A newly synthesized antioxidant 3,5-ditert.butyl-4-hydroxybenzyl thioglycollate (DBHBT) and Tinuvin P have been used as additives for normal ABS. The thermal and photo-oxidative stabilities of the polymer containing these additives have been compared with those for unstabilized ABS. It is concluded that the new additive gives very good thermal stability to ABS and acts as a peroxide decomposer. It was found that it could be grafted on to the polymer backbone during processing. Synergism was obtained with a combination of Tinuvin P and DBHBT. It was found that considerable protection was offered to the base polymer when ABS containing these additives was exposed to weathering.     

Process splitting of the boundary conditions for the advection–dispersion equation

Rational strategies are considered for the specification of the intermediate boundary condition at an inflow boundary where process splitting (fractional steps) is adopted in solving the advection–dispersion equation. Three lowest-order methods are initially considered and evaluation is based on comparisons with an analytical solution. For flow and dispersion parameter ranges typical of rivers and estuaries, the given boundary condition for the complete advection–dispersion equation at the end of the complete time step provides a satisfactory estimate of the intermediate boundary value. This was further confirmed by the development and evaluation of two higher-order methods. These required non-centred discrete approximations for spatial derivatives, which offset any special advantages from the higher truncation error order.