Here, we report all-polymer polysiloxane composites that overcome the long-standing processing problems of silica-reinforced silicone rubbers. Polystyrene fillers are dispersed with styrene/dimethylsiloxane symmetric diblock and triblock copolymers that control the filler morphology, filler−matrix interactions, and filler−filler interactions. Surprisingly, the composites not only rival the traditional silica-reinforced polysiloxane in mechanical properties of cured materials but also have better processability and stability than the silica-filled compound before curing. Large amplitude oscillatory shear experiments demonstrate that the triblock copolymer addition strongly affects the rheological properties. We hypothesize that the bridges and entangled loops that were formed by the triblock copolymer can connect different PS domains to provide additional reinforcement. The aging effect that originates from PDMS chain adsorption on the filler particle surface is also avoided because of the thermodynamic repulsion between PS and PDMS phases.
Here we present an approach for selectively modifying the properties of semicrystalline polymers by introducing "bioadvantaged" counits. With this approach, the unique functionality of biomass can be leveraged to tailor the properties of the amorphous phase of semicrystalline polymers with minimal impact on crystallinity and thermomechanical properties. As a model case, PA 6,6 copolyamides were produced using the bioadvantaged monomer trans-3-hexenedioic acid (t3HDA). The analogous structure of t3HDA to adipic acid, a PA 6,6 monomer, allows for seamless integration. Screening over the entire composition range identified the t3HDA loading (20 mol%) beyond which properties deviate appreciably from Nylon 6,6. Once identified, copolyamides of suitable compositions were upgraded to commercial quality and fully characterized to assess the influence of counit loading and polymer structure on thermal and mechanical properties. Samples were characterized using gel permeation chromatography (GPC), proton nuclear magnetic resonance spectroscopy ( 1 H NMR), heteronuclear single quantum coherence spectroscopy (HSQC), wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), tensile testing, flexural testing, and water absorption testing. t3HDA units were shown to hydrate during the harsh polycondensation to 3-hydroxyhexanedioic acid (3HHDA) and fully incorporate into the polymer backbone. Loading levels up to 20% were shown to have comparable thermal and mechanical properties in the dry state, yet moisture absorption-a known method for improving the toughness, yield strain, and elongation of polyamides-
Glycerol, a water-soluble polyol, is currently used in a wide variety of markets, e.g. as a sweetener in drinks, as an additive in the food and cosmetics industry, or as an antifreeze agent, to name a few. The blooming biodiesel production has created an excess supply of glycerol by-product. Researchers all around the world are actively exploring strategies to utilize this cheap and abundantly available biobased molecule. To date, glycerol-based polymers have only been examined extensively for use in biomedical applications; however, the use of biobased crude glycerol is not viable for such applications due to the presence of impurities such as methanol and residual fatty acids from the biodiesel production process. However, the increased volumes of glycerol generated from biodiesel production have stimulated the research on its use in various other industrial applications such as the production of commodity chemicals, polymers etc. In this article, we summarize some of the efforts to valorize glycerol for polymeric applications such as polyurethanes, polyhydroxyalkanoates and adhesives.
Cyanate esters (CEs) are an important class of materials among high-temperature-performance thermosets. They are used in aerospace launch vehicles, heat sinks, booms, trusses of satellites, etc., due to their high glass transition temperatures (>220 °C), excellent thermal stability, and low flammability. Current approaches to improve the thermal stability of CEs include incorporation of siloxanes or phosphorus-based flame retardants. In this work, we have explored boron-based hydroxy (PD)-and epoxy (EP)functionalized carborane additives to improve the thermal properties of CEs. Carborane fillers were solvent-blended at various mass loadings in the resin and cured to study their effect on thermal properties. PD and EP carboranes react with CEs to form iminocarbonates and oxazolidinone linkages, respectively. Cure kinetic studies at different wt % loadings explained that carboranes catalyze the curing reaction by reducing the curing activation energy by about 54 and 26% for 10 wt % loadings of PD and EP carboranes, respectively. In addition, carborane-filled CE nanocomposites demonstrate an exceptionally high thermal stability as compared to the pristine resin in air and inert environments. Our thermogravimetric analysis (TGA) experiments show that the ultimate char yield of the resin can be increased from 0% to as high as 76 and 82% with 30 wt % PD and EP carborane loadings, respectively, at 1000 °C in air. The initial degradation temperature T d,5 of the composites decreased with increasing carborane loadings in both air and argon. For instance, T d,5 values for CE were 465 and 471.6 °C in argon and air, while those for P20 were 437.4 and 452.1 °C, respectively. Modulated TGA studies gave evidence of the effect of carboranes on degradation mechanism and kinetics in air and inert environments. The effect of bonding between carboranes and CEs at various loadings on the thermal expansion of the matrix was also studied using a thermomechanical analyzer. PD carborane reduced the T g for P20 to about 225 °C, while CE had T g > 350 °C.
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