No abstract

Are hyperbranched polymers capable of forming entanglements? This is the central issue of this contribution. Hyperbranched polyglycerol (hbPG) samples with different molecular weights (600-106 000 g · mol(-1) ), narrow polydispersities (1.2-1.8) and high degrees of branching (≈0.6) were prepared by anionic ring-opening polymerization. The viscoelastic properties of these polymers with respect to molecular architecture and molar mass were investigated. At low molecular weights "classical" scaling behavior between zero shear viscosity and molecular weight can be observed, whereas between 3 000 and 10 000 g · mol(-1) a plateau-like area is found. The results indicate entanglement dynamics when exceeding a critical molar mass ($\overline {M} _{{\rm c}}^{*} $ ≈ 20 000 g · mol(-1) ) due to entangled hyperbranched polyglycerols.

Every year 23 % of the world energy consumption is caused by friction and wear. Especially now and in future bearings and gear boxes will be exposed to electrical currents so lubricants have to prevent the components from new damage mechanism. The usage of Ionic Liquids as conductible lubricant additives is in discussion for a longer period of time, but right now it was not investigated how these liquids could be affect by electrical currents itself. Generally, lubricants in industry are compounded by base oils, additives, and thickeners. All these ingredients are isolators and not able to discharge electrical currents. In these joint research project, different Ionic Liquids with different conductivities have been exposed to defined electrical currents. For that experiments a new current feed setup has been developed, where the liquids and model lubricants were exposed to electrical currents under temperature control. The influence on the liquids by the current feed was chemically quantified by using IR-Spectroscopy, rheology and conductivity measurements. The Ionic Liquids react, depending on their chemical structure, very different on the current feeds, some of them has been destroyed totally.