Crosslinking of poly(vinyl acetate) nanolatices by gamma and UV radiation

Poly(vinyl acetate) PVAc, in nanolatices with 10% polymer content, prepared by microemulsion polymerization was crosslinked by gamma and UV radiation. PVAc colloidal nanoparticles (average diameter, Dp = 58 nm) had M_w = 562,000 g/mol and about 95% conversions. PVAc nanolatices irradiated by gamma rays (1–13 kGy) at room temperature without crosslinking agent and by UV light (30–300 s exposure times) in the presence of divinylbenzene and allyl methacrylate showed crosslinking of up to 96% (high gel content), Dp < 100 nm and did not degrade as shown by FTIR spectroscopy. DSC and TGA characterization of irradiated PVAc samples indicated that T_g temperatures increased from 28°C for PVAc to 42°C and 39°C for UV and gamma rays crosslinked PVAc, respectively, whereas 10% weight losses occurred at 261°C for uncrosslinked PVAc and at 320 and 313°C for UV and gamma rays crosslinked PVAc. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Removal of toxic uranium from synthetic nuclear power reactor effluents using uranyl ion imprinted polymer particles

Major quantities of uranium find use as nuclear fuel in nuclear power reactors. In view of the extreme toxicity of uranium and consequent stringent limits fixed by WHO and various national governments, it is essential to remove uranium from nuclear power reactor effluents before discharge into environment. Ion imprinted polymer (IIP) materials have traditionally been used for the recovery of uranium from dilute aqueous solutions prior to detection or from seawater. We now describe the use of IIP materials for selective removal of uranium from a typical synthetic nuclear power reactor effluent. The IIP materials were prepared for uranyl ion (imprint ion) by forming binary salicylaldoxime (SALO) or 4-vinylpyridine (VP) or ternary SALO-VP complexes in 2-methoxyethanol (porogen) and copolymerizing in the presence of styrene (monomer), divinylbenzene (cross-linking monomer), and 2,2'-azobisisobutyronitrile (initiator). The resulting materials were then ground and sieved to obtain unleached polymer particles. Leached IIP particles were obtained by leaching the imprint ions with 6.0 M HCl. Control polymer particles were also prepared analogously without the imprint ion. The IIP particles obtained with ternary complex alone gave quantitative removal of uranyl ion in the pH range 3.5-5.0 with as low as 0.08 g. The retention capacity of uranyl IIP particles was found to be 98.50 mg/g of polymer. The present study successfully demonstrates the feasibility of removing uranyl ions selectively in the range 5 microg - 300 mg present in 500 mL of synthetic nuclear power reactor effluent containing a host of other inorganic species.     

Mathematical model for the bulk polymerization of styrene using the symmetrical cyclic trifunctional initiator diethyl ketone triperoxide. I. Chemical initiation by sequential decomposition

In this study, we experimentally and theoretically investigated the use of the symmetrical cyclic trifunctional initiator diethyl ketone triperoxide (DEKTP) in the bulk polymerization of styrene. The experimental study consisted of a series of isothermal batch polymerizations at different temperatures (120 and 130°C) with different initiator concentrations (0.005, 0.01, and 0.02 mol/L). A mathematical model was developed to predict the evolution of the reacting chemical species and the produced molecular weight distributions. The kinetic model included chemical and thermal initiation, propagation, transfer to the monomer, termination by combination, and reinitiation reactions. The simulation results predict the concentration of diradicals, monoradicals, and polymeric chains, characterized by the number of undecomposed peroxide groups. The experimental results showed that at reaction temperatures of 120–130°C, initiation by DEKTP produced an increase in the polymerization rates (R_p's) and average molecular weights, depending on the initiator concentration, due to sequential decomposition. The mathematical model was adjusted and validated with the experimental data. The theoretical predictions were in very good agreement with the experimental results. Also, an optimum initiator concentration was observed that achieved high R_p's and high molecular weights simultaneously. For polymerization temperatures of 120–130°C, the optimum concentration was 0.01 mol/L. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

A Lamarckian Approach for Neural Network Training

In Nature, living beings improve their adaptation to surrounding environments by means of two main orthogonal processes: evolution and lifetime learning. Within the Artificial Intelligence arena, both mechanisms inspired the development of non-orthodox problem solving tools, namely: Genetic and Evolutionary Algorithms (GEAs) and Artificial Neural Networks (ANNs). In the past, several gradient-based methods have been developed for ANN training, with considerable success. However, in some situations, these may lead to local minima in the error surface. Under this scenario, the combination of evolution and learning techniques may induce better results, desirably reaching global optima. Comparative tests that were carried out with classification and regression tasks, attest this claim. This revised version was published online in June 2006 with corrections to the Cover Date.     

Age differences in repeated learning tasks in schizophrenic subjects.

This experiment was designed to study age differences in the learning of paired associates in serial order and a card-sorting task over 9 different sessions. The Ss consisted of 2 groups, 15 younger-aged (20-29) and 15 middle-aged (40-56), male, hospitalized schizophrenics. The results indicated that the younger-aged-group's performance was superior on both tasks for the 1st session. Over the 9 learning sessions the middle-aged group showed significantly greater improvement on the paired-associate task, while the differences between the age groups in card-sorting speed remained fairly constant over the 9 sessions. It was concluded that the learning deficit in middle-aged and schizophrenic Ss is something that is not a fixed and immutable one for all tasks but may be modified through practice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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