Impact of ocean acidification on a key Arctic pelagic mollusc (Limacina helicina)

Thecosome pteropods (shelled pelagic molluscs) can play an important role in the food web of various ecosystems and play a key role in the cycling of carbon and carbonate. Since they harbor an aragonitic shell, they could be very sensitive to ocean acidification driven by the increase of anthropogenic CO2 emissions. The impact of changes in the carbonate chemistry was investigated on Limacina helicina, a key species of Arctic ecosystems. Pteropods were kept in culture under controlled pH conditions corresponding to pCO2 levels of 350 and 760 μatm. Calcification was estimated using a fluorochrome and the radioisotope 45Ca. It exhibits a 28% decrease at the pH value expected for 2100 compared to the present pH value. This result supports the concern for the future of pteropods in a high-CO2 world, as well as of those species dependent upon them as a food resource. A decline of their populations would likely cause dramatic changes to the structure, function and services of polar ecosystems

Anionic Synthesis of Thermally and Hydrolytically Stable Telechelic Polysiloxanes

peer reviewedaudience: researcher[No abstract available

Block Copolymerization of 3, 3-Dimethyl-2-oxetanone. 1. About the Mechanism of a, a-Disubstituted β-Propiolactones Block Copolymerization

peer reviewedaudience: researcherBlock copolymerization of 3, 3-dimethyl-2-oxetanone (or pivalolactone, PVL) has been reported by different authors by applying an anionic process initiated by carboxylate salt end groups. A living (co)polymerization of PVL is observed, and the mechanism could be assume as being of wide application. However, in every successful block PVL copolymerization described, a polarizable group is present in the vicinity of the initiating carboxylate salt. From our observations, it is concluded that the absence of such a structural feature is responsible for PVL homopolymerization. Accordingly, the initiating carboxylate end group cannot be free but must be interacting with a neighboring polarizable group to avoid this unexpectedly drastic limitation. The extension of this requirement to the PVL grafting processes has not been ascertained. © 1979, American Chemical Society. All rights reserved

Graft copolymers as stabilizers of san dispersions in polyether-polyols and and ultimately in polyurethane foams

audience: researcherSeveral patents claim that thermoplastic particles, and particularly poly(styrene-coacrylonitrile) (SAN) particles, can be dispersed in liquid polyether-polyols, using a graft copolymer as a steric stabilizer. This paper reports another technique able to stabilize SAN (80 wt% styrene and 20 wt% acrylonitrile) dispersions in such a way that the in-situ generated stabilizer is very effective and as well defined as possible. Variations in the molecular characteristics of a double comb graft copolymer used as a steric stabilizer in dispersions of SAN particles in a liquid polyol allow dispersion properties, such as stability, particle size and viscosity to be controlled and optimized. Load bearing property of PU foams is best improved when they are modified by a stable dispersion of rather small SAN particles. These solid polymer/polymer dispersions are actually controlled by the double comb graft copolymer that stabilized the original solid/liquid system. When the mutual anchoring of the solid polymer phases is properly controlled, tear resistance and tensile strength of foams are improved, whereas elongation is kept at an acceptable level

Catalysis of the reaction between isocyanates and protonic substrates. II. Kinetic study of the polyurea foaming process catalyzed by a series of amino compounds

peer reviewedaudience: researcherThe catalytic activity of secondary and tertiary amines were determined in the reaction of phenyl isocyanate with water and aniline, respectively, in dioxane at 25°C. The polyurea formation is largely controlled by a base‐type catalysis. However, this general behavior can be perturbed by steric factors, and still more obvious deviations appear with protic catalysts reacting rapidly with the isocyanate. The resulting urea or urethane groups can display a significant activity in relation to the nature and the composition of the reaction medium. Very good quality foams can be obtained with these protic catalysts. Copyright © 1982 John Wiley & Sons, Inc

Synthesis and Characterization of Polymethylphenylsilane-polystyrene Block-copolymers

Block copolymers of polymethylphenylsilane (PMPS) and polystyrene (PS) have been successfully prepared by the condensation of alpha,omega-dichloro-polymethylphenylsilane with polystyryl-lithium. These new materials have been characterized by UV spectroscopy, Si-29-NMR, and size exclusion chromatography. These block copolymers show a good emulsifying activity to compatibilize blends of the two homopolymers (PMPS and PS)

Examination of the preparation of a block copolymer from macroradicals produced in viscous media

Extensive experiments on copolymer syntheses as a type of dispersion polymerization in viscous poor solvents (e.g., silicone oil) have been reported (Seymour, R. B.; Kincaid, P. D.; Owen, D. R. Adv. Chem. Ser. 1973, 129, 230) which, based on a trapped-macroradical model, were taken to suggest that such conditions promoted the formation of block copolymers. Here we report the results of a series of tests devised to elucidate the mechanisms in these systems. One such test used initiation by γ radiolysis of water, which allows virtually instantaneous cessation of the production of primary radicals after removal from the γ source. This resulted in a very rapid drop in the polymerization rate. This observation constitutes what seems to be irrefutable evidence against the trapped macroradical model, which would predict that the polymerization should continue at a moderate rate after removal from the source. Furthermore, it is shown that in these viscous-solvent dispersion polymerizations, there is a significant rate of production of free radicals under conditions where the original interpretation implied that this would not be the case. Moreover, it is shown that the formation of graft copolymers can result from the transfer reaction of primary free radical with the preformed homopolystyrene backbone. The original erroneous interpretation (in terms of formation of block copolymers from trapped macroradicals) can thus have arisen because the distinction between block and graft copolymer was beyond the resolving power of the analytical technique used to characterize the products. The results of the present experiments and those of Seymour can be readily explained in terms of rapid termination between two long macroradicals encountering each other through reaction/diffusion and/or between an entangled macroradical and a mobile oligomeric free radical formed by transfer