Superconnectivity of regular graphs with small diameter

A graph is superconnected, for short super-κ, if all minimum vertex-cuts consist of the vertices adjacent with one vertex. In this paper we prove for any r-regular graph of diameter D and odd girth g that if D≤g−2, then the graph is super-κ when g≥5 and a complete graph otherwise.     

The rôle of chain ends in the thermal degradation of anionic polystyrene

Direct evidence is given of the initiating rôle played in the thermal degradation of anionic polystyrene by chain ends, either present originally or formed during the degradation. In the early stages of degradation, the most likely bond scission in polystyrenes with benzylic type units (CH₂(C₆H₅)) at both chain ends involves the formation of toluene and an unsaturated terminal unit (CH₂C(C₆H₅)CH₂). The depolymerisation of polystyrene to a mixture of monomer and dimeric, trimeric, etc., fragments is then initiated by further scission at such unsaturated chain ends, giving α-methyl styrene and a depolymerising macroradical.After the early stage of degradation, a further overwhelming contribution to the formation of unsaturated chain ends is derived from chain transfer which occurs during depolymerisation. The concentration of unsaturated chain ends increases throughout the degradation process, thus accelerating the formation of the volatile products of depolymerisation. According to this mechanism of initiation, a constant ratio is found between rates of weight loss and of α-methyl styrene evolution throughout the degradation, independently of the original molecular weight of the polymer.     

Polvmerisation von unkonjugierten Dienen mit freien Radikalen. 16. Mitt. Temperaturabh?ngigkeit des Cyclisierungsverh?ltnisses bei der Cyclopolymerisation von Methacryls?ureanhydrid

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Thermal degradation of phosphonated polystyrenes: Part 2—The volatilisation step

On heating at volatilisation temperatures, polystyrene (PS) and telechelic chloromethoxyphosphonated polystyrene (TPPS) behave differently in the very early stage of the process. The initial rate of volatilisation of PS is zero and increases with conversion whereas TPPS polymers volatilise at an initial high rate which decreases with conversion. However, in the main stage of volatilisation (from 10–20 to 70% weight loss) both polymers liberate the same volatile products through the same basic mechanism of depolymerisation. Nevertheless, the overall rate of volatilisation of TPPS polymers in this stage is much lower than that of PS. This is attributed to the creation in degrading TPPS polymers of less reactive chain carriers of the depolymerisation process which are stabilised by the phosphoryl group.     

Enantioselective hydrogenation of alkenes and imines by a gold catalyst

A new neutral dimeric gold(I) complex bearing the 1,2-bis[(2R,5R)-2,5-dimethylphospholanebenzene] [(R,R)-Me-Duphos] ligand has been synthesized which catalyzes the asymmetric hydrogenation of alkenes and imines under mild reaction conditions.     

Study of the mechanism of intumescence in fire retardant polymers: Part I—Thermal degradation of ammonium polyphosphate-pentaerythritol mixtures

Interactions are shown to take place between ammonium polyphosphate and pentaerythritol in thermally degrading mixtures. Up to 500°C, gaseous products are evolved on programmed heating above 200°C in two steps with maximum rate temperatures differing by about 100–150°C. Swelling of the degrading mass seems, however, to be mainly due to gases evolved in the step occurring at the higher temperature. A strong dependence of the degradation process on the experimental conditions is observed.     

Ammonium polyphosphate-aluminum trihydroxide antagonism in fire retarded butadiene-styrene block copolymer

In this paper the effect of aluminum trihydroxide (Al(OH)₃—ATH) on the surface protection from fire for a styrene butadiene rubber (SBR) provided by ammonium polyphosphate ([NH₄PO₃]_n—APP) is studied.The combustion behaviour is studied by means of Cone Calorimetric tests: a maximum fire retardant effect is observed with 10-12 wt.% of APP. ATH, less effective as fire retardant, has been added at 60 wt.% to reach comparable results as measured by cone calorimetry for 12 wt.% APP.Replacement of ATH in the best performing SBR + 12 wt.% of APP shows an antagonistic effect with as little as 1 wt.% of ATH.The combustion behaviour is explained with the mechanism of interaction between SBR, APP and ATH, in which formation of aluminum phosphates negatively affects the surface protection provided by the ultraphosphate surface coating formed on heating APP in SBR.     

Thermal degradation of copolymers of methyl methacrylate and 2,6-dimethoxycarbonyl-1,6-heptadiene

The thermal degradation under vacuum of copolymers of methyl methacrylate and 2,6-dimethoxycarbonyl-1,6-heptadiene of different compositions has been investigated. It has been found that the presence in the polymer chains of small amounts of cyclic structural units from the diene monomer considerably reduces the amount of degradation which occurs in poly(methyl methacrylate) at temperatures lower than 300°C. On the basis of the results of the analysis of the degradation products, a mechanism is suggested which accounts for this effect.     

The use of POSS as synergist in intumescent recycled poly(ethylene terephthalate)

Fire retarded poly(ethylene terephthalate) (PET) has been obtained by the incorporation of octamethyl polyhedral oligomeric silsesquioxane (OMPOSS) and Exolit OP950, a phosphinate-based compound, in recycled PET. The presence of Exolit OP950 only leads to intumescence explaining the improvement of the flame retardancy. The addition of OMPOSS leads to a synergistic effect considerably increasing the fire retarding performances of the polymer in terms of cone calorimetry and limiting oxygen index even if a small thermal stabilisation as well as a very poor dispersion of OMPOSS and OP950 into the matrix has been observed.