Elastomeric Gels Research Articles

Monodomain liquid crystal elastomers and elastomeric gels: Improved thermomechanical responses and phase behaviour by addition of low molecular weight LCs

Large monodomain-liquid crystal elastomer films have been prepared using mechanical alignment, either as pure materials or as gels doped with low molecular weight chiral liquid crystals. The thermomechanical strain behaviour of the resulting materials has been studied over a range of temperatures. The largest thermal strains have been achieved when the mechanical alignment was carried out in the smectic A phase, just below the transition to the apparent isotropic liquid phase. The pure elastomers exhibit thermomechanical responses over broad temperature ranges (ca. 60 °C), however the elastomer gels doped with a low molecular weight LC exhibit significantly sharper thermomechanical responses over a narrower temperature range (ca. 15 °C).

Calibration of cyclohexane solid–solid phase transition thermoporosimetry and application to the study of crosslinking of elastomers upon aging

Photo-aging of elastomers results in two competitive processes: chain- scissions and crosslinking. The solid-to-solid cyclohexane phase transition was used to investigate the crosslinking extent in photo-oxidised ethylene propylene diene monomer (EPDM) samples by thermoporosimetry technique. Before apply this technique to EPDM, texturally well-known silica gel samples were used to calibrate the method. By contrast to the case of liquid-to-solid heptane transition, no linear relationship was obtained between the solid-to-solid point depression (Δ T) and the pore radius ( R p). The following correlation was obtained: R p ( A ̊ )=16.93+125.43 exp − 1/ ΔT+0.0756 0.0205 with 0> ΔT>−55 ° C. Pore size distributions (PSD), calculated by thermoporosimetry using the solid-to-solid transition, were in a good agreement with those obtained by gas sorption method (BJH). Elastomeric gels were assumed to be similar to a porous medium where the pore notion is replaced by the mesh notion. Using the same relations which were used to calculate the PSD, the mesh size distributions (MSD) were calculated for various EPDM samples crosslinked under irradiation. The width and the maximum of these MSD are related to the extent of crosslinking.

Elastomeric polyacrylamide gels for high‐resolution electrophoresis of proteins

Elastomeric polyacrylamide gels for high‐resolution electrophoresis of proteins

Elastomeric polyacrylamide gels for high-resolution electrophoresis of proteins

Elastomeric polyacrylamide gels for high-resolution electrophoresis of proteins

Synthesis and characterisation of Ti(IV) and Zr(IV)-containing elastomeric polysiloxane networks: a possible route to interesting heterogeneous catalysts

Polysiloxane gels have been prepared in bulk and in non-aqueous suspension using an oligomeric dimethyl silanol, S5 or S10, and tetraethoxysilane (TEOS) as the main reactants, with a tin-based catalyst. Controlled levels of Ti and Zr have been introduced into the polysiloxane networks by replacing part of the TEOS by either Ti tetraisopropoxide (TIPO) or Ti tetrakis(2-ethylhexyl oxide) (TEHO) in the case of Ti, and Zr tetraisopropoxide (ZPO) in the case of Zr. Providing TEOS is maintained as the major crosslinking component, toluene insoluble gels are formed with Ti and Zr covalently incorporated into the network. The Ti- and Zr-containing elastomeric polysiloxane gels have been used as heterogeneous catalysts in the epoxidation of cyclohexene using tBHP or 30% aqueous H2O2. With the former oxidant the gels are indeed active and selective catalysts; however, essentially no activity was observed when aqueous H2O2 was employed. The structure of the gels and their role in catalysis is discussed in the context of Ti and Zr-containing zeolite and other mixed oxide catalysts.

Triblock copolymer based thermoplastic elastomeric gels of a large service temperature range: preparation and characterization

AbstractPoly(methyl methacrylate)‐block‐polybutadiene‐block‐poly(methyl methacrylate) (MBM) triblock copolymers and their hydrogenated counterparts with poly(ethylene‐co‐1,2‐butylene) midblock (MEBM) were swollen by an aliphatic oil of high boiling point which is a selective solvent for the central block. Thermoreversible gels are accordingly formed by both MBM and MEBM copolymers above a critical polymer content (Cr), which depends on the nature of the midblock and not on the copolymer molecular weight, at least in the investigated range. Cr has been found to be 5 wt.‐% for an MBM block copolymer and 2 wt.‐% for MEBM copolymers of various molecular weights. Gels of MEBM triblock copolymers exhibit interesting mechanical properties, such as high elongation at break (up to 870%) and high tensile strength (32 kPa). The most interesting feature of the MEBM gels is an upper service temperature as high as 170°C, thus more than 100°C higher than the value (47°C) reported for gels of an SEBS copolymer (S = polystyrene) of comparable molecular weight (100000) and composition (ca. 30 wt.‐% hard block). The morphology of MEBM gels was studied by scanning electron microscopy (SEM) and found to be cocontinuous in case of a gel containing 20 wt.‐% copolymer.

Preparation of Propylene Carbonate Acrylate and Poly(propylene carbonate acrylate) Electrolyte Elastomer Gels. 13C NMR Evidence for Li+-Cyclic Carbonate Interaction

The phosgene-free synthesis of fast curing (2-oxo-1,3-dioxolan-4-yl)methyl acrylate (propylene carbonate acrylate, PCA) is presented. Polymerization of PCA in the presence of plasticizing propylene carbonate (PC) results in the formation of reversibly swellable elastomeric gels. The ionic conductivity of poly(PCA) plasticized with 50 wt % PCA and containing 1 M lithium triflate is 1.7×10 -5 S/cm. Evidence for Li + -cyclic carbonate interaction was found in 13 C CP-MAS NMR spectroscopic analysis of the model compound poly(vinylene carbonate) containing 1 M lithium triflate

A bifunctional anionic initiator soluble in non‐polar solvents

AbstractAddition of two molecules of sec‐butyllithium to one molecule of m‐diisopropenylbenzene produces a bifunctional initiator which is soluble in non‐polar solvents. This initiator is quite efficient for the polymerization of isoprene and butadiene and allows the preparation of samples of particular interest: bifunctional polydienes with high 1,4‐cis and 1,4 contents, respectively, and by using a cross‐linking agent elastomeric gels even after removal of the solvent.