Reactive surfactants in heterophase polymerization. XVII. Influence of the surfactant on the mechanical properties and hydration of the films

In the context of a European union‐supported network on “Reactive Surfactants for Heterophase Polymerization,” different polymerizable surfactants (surfmers) have been synthesized and engaged in the emulsion polymerization of styrene, butyl acrylate, and acrylic acid. The thermomechanical properties of films cast from these different latices are reported in this article. The evolution of the mechanical properties with temperature and the effect of water molecules on these properties are studied. We observed that the studied surfactants do not influence the properties of the dry films. However, some differences due to grafting of reactive surfactants appeared when the films were wet. The amount of water uptake is drastically decreased when only reactive surfactants are present in the film. Concerning the mechanical behavior of the wet films, a decrease of the plastic flow stress is observed for all the samples whatever the nature of the surfactant (reactive or conventional). Hence, calorimetric measurements and dynamic mechanical analysis are used to identify the possible mechanisms that induce the change in the mechanical behavior of the latex films. In the case of reactive surfactant grafted to the polymer, the very low value of water uptake is accompanied by a plasticization of the polymer. In contrast, no plasticizing effect is observed in the case of nonreactive surfactant, even if the amount of water is very large. Finally, the tensile behavior of the styrene–butyl acrylate copolymer versus temperature is analyzed in the frame of the quasi point defects (qpd) model. Both rubber elasticity and chain orientation effects are taken into account to describe the behavior laws at large extensions (i.e., ? ≈ 1.2). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1686–1700, 2002; DOI 10.1002/app.10548     

Modeling the evolution of the dynamic mechanical properties of a commercial epoxy during cure after gelation

The cure kinetics for a commercial epoxy have been established and the influence of the degree of cure on the glass transition determined. Time‐temperature and time‐conversion superposition principles have been built into a model that successfully predicts the development of the viscoelastic properties of the epoxy during isothermal cure from gelation to after vitrification. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 495–508, 2000     

Reactive surfactants in heterophase polymerization. XVI. Emulsion copolymerization of styrene–butyl acrylate–acrylic acid in the presence of simple maleate reactive surfactants

This study deals with the influence of a copolymerizable surfactant on the stability of lattices. Two main reactive surfactants, one anionic and one nonionic, both containing a reactive part issued from maleic anhydride, were engaged in seeded emulsion polymerizations of styrene‐co‐butyl acrylate‐co‐acrylic acid. The importance of the polymerization conditions clearly appears through the incorporation yield of the surfmers: When good conditions are used, this yield can be as high as 80%. Once stable lattices are synthesized, with a great incorporation of the surfactant, the stability of the colloid (against freeze–thawing cycles or in the presence of concentrated divalent electrolyte solutions) is then largely improved. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2768–2776, 2000     

Effect of sequential implanting with Synovex on steer and heifer performance

Studies were conducted using 72 (Exp. 1) and 248 (Exp. 2) steer and heifer calves from 1 to 2 mo of age through slaughter to determine whether preweaning implants affect postweaning feed conversion of cattle that are rapidly grown and(or) finished in the feedlot. In Exp. 1, treatments were three Synovex (S) implants administered 0, 70, and 140 d postweaning (NSSS) or Synovex-C (C) administered preweaning and three implants administered postweaning (CSSS). In Exp. 2, treatments were no implants (NNNN), implants administered 0, 74, and 148 d postweaning to calves that had either received no preweaning implant (NSSS), or C (CSSS), and CSSS plus trenbolone acetate (TBA) administered with the last S implant (CSSS-TBA). Synovex-S or -H implants were administered postweaning to steers and heifers, respectively. Steer and heifer calves implanted with C in the preweaning phase were 9.0 and 13.0 kg (Exp. 1) and 7.5 and 15.0 kg (Exp. 2) heavier (P < .10), respectively, at weaning than nonimplanted steer and heifer calves. In Exp. 1, preweaning implant had no affect on postweaning performance or quality grade. In Exp. 2, preweaning implants (NSSS vs CSSS) decreased (P < .10) steer postweaning gains, whereas postweaning implants (NSSS vs NNNN) increased (P < .10) DM intake; however, feed:gain ratio was not affected by implant strategy. Heifers in Exp. 2 that received implants had greater postweaning (P < .10) DM intakes and daily gains than heifers not receiving implants (NNNN); however, feed:gain ratios among treatment groups were unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)