No abstract

A series of controlled microstructure polybutadiene rubbers (PBs) was synthesized via anionic polymerization. Their structure and properties are analyzed by means of GPC, 13 C NMR, DSC, and DMA, and compared to the behavior of some commercial high cis rubbers. Thermal analyses results indicate the presence of crystalline domains of different nature in PBs with high cis-1,4 and high trans-1,4 isomers content, while rubbers with high content of vinyl-1,2 units do not show evidence of crystals. A shift in T g to higher temperatures as vinyl content increases is observed; an expression was found for predicting T g of rubber from microstructure data.

No abstract

The ruthenium complex with (N,N,N-tris(benzimidazol-2yl-methyl)amine, L(1)) was prepared, and characterized. Fukui data were used to localize the reactive sites on the ligand. The structural and electronic properties of the complex were analyzed by DFT in different oxidation states in order to evaluate its oxidant properties for phenol oxidation. The results show that the hard Ru(IV) cation bonds preferentially with a hard base (Namine = amine nitrogen, or axial chloride ion), and soft Ru(II) with a soft base (Nbzim = benzimidazole nitrogen or axial triphenyl phosphine). Furthermore, the Jahn-Teller effect causes an elongation of the axial bond in the octahedral structure. The bonding nature and the orbital contribution to the electronic transitions of the complex were studied. The experimental UV-visible bands were interpreted by using TD-DFT studies. The complex oxidizes phenol to benzoquinone in the presence of H2O2 and the intermediate was detected by HPLC and (13)C NMR. A possible mechanism and rate law are proposed for the oxidation. The adduct formation of phenol with [Ru(O)L(1)](2+) or [Ru(OH)L(1)](+) is theoretically analyzed to show that [Ru(OH)L(1)-OPh](+) could produce the phenol radical.

Asphalt‐modification was studied using two different types of triblock copolymers both with star‐like molecular architecture: poly(styrene‐b‐butadiene‐b‐styrene), SBS, and poly(styrene‐b[(butadiene)1−x‐(ethylene‐co‐butylene)x]‐b‐styrene), SBEBS, to elucidate the effect of the molecular characteristics of the polymer and the polymer‐content on the morphology and rheological behavior of polymer‐modified asphalt, P‐MA. The P‐MAs were prepared using a hot mixing process and characterized using fluorescence microscopy and oscillatory shear flow measurements under linear viscoelastic conditions. Results revealed that the morphology of the polymer‐rich phase and rheological behavior of the P‐MA are dependent on the type and concentration of polymer: (i) P‐MAs prepared with SBEBS exhibited higher dispersion in the asphalt matrix and were more elastic and less responsive toward frequency changes; (ii) P‐MAs prepared with the polymer (SBS or SBEBS) of the larger molecular weight displayed higher elasticity; and (iii) the increase in the polymer concentration from 3 to 10 wt% resulted in the creation of P‐MAs with higher elastic response. These results substantiate the importance of the molecular characteristics of the polymer in determining the properties of P‐MAs, in particular composition of the elastomeric‐b and molecular weight of these polymers, and the results are explained considering the molecular characteristics of these polymers and the polymer/asphalt interaction. POLYM. ENG. SCI., 53:2454–2464, 2013. © 2013 Society of Plastics Engineers

Polymersomes are synthetic vesicles that imitate biological membrane functions. The purpose of this work is to develop an artificial copolymer (acrylic acid=butyl acrylate) PAA-PBA membrane by random synthesis. A factorial design 2 k was applied to determine the conditions for this reaction. The Fourier transform infrared spectrometer indicated that the polymerization reaction was complete without a -C¼C-absorption peak. The Gordon-Taylor equation showed that the hydrophilic part of the PAA-PBA composition is 20-40% and the hydrophobic part 60-80%. The authors selected the copolymers with low molecular weight, within the range of 3134.49 AE 994.21 g=mol and a polydispersity of 1.40.

Using a single flow-type parameter, we obtain analytic expressions for the unsteady and steady stress distribution for upper-convected Maxwell fluids in mixed shear and planar extensional flows, experimentally achieved in a four-roll mill. We propose two expressions to quantify the shear and extensional contributions to the strain rate magnitude. Finally, we conduct an analysis on the appearing rheological functions by defining apparent shear viscosity as a function of the flow-type parameter and the Weissenberg number.

The current work reports the effect of particle size on the rheological behavior of polymer modified asphalt PMA. The modified asphalt was generated with AC-20 asphalt precursor provided by Pemex Salamanca and Solprene® 416 provided by Dynasol Mexico. Solprene® 416 is a SBS star-type copolymer with 4 poly(b-styrene-b-butadiene) arms and Mw = 2.36X105 g/gmole. Modified asphalt samples were prepared with 3 wt % of SBS via hot mix process. Mixing time and temperature were kept constant at 4h and 180 °C. This study also varied the agitation in the mixing process: 500, 1000 and 1500 rpm. All PMAs shown sphere-shaped polymer particles as observed via fluorescent microscopy using a Carl Zeiss KS-300 system. Base asphalt and PMAs were also characterized through rheological measurements using a TA Instruments AR-G2 rheometer. Shear viscosity (η) and tan δ data shown that the flow resistance of the PMA increases as the size its polymer particles decreases. Since the size of the polymer particles decreases with the increase of the stirring speed, it is concluded that the stirring speed of the process determines the size of the polymer particles and so the mechanical resistance of the PMA.