Hyperbranched glycopolymers were grafted from a silicon wafer with a covalently attached initiator layer of α-bromoester fragments using self-condensing vinyl copolymerization (SCVCP) of the methacrylic AB* inimer, 2-(2-bromoisobutyryloxy)ethyl methacrylate (BIEM), and a sugar-carrying methacrylate, 3-O-methacryloyl-1,2:5,6-di-O-isopropylidene-α-d-glucofuranose (MAIGlc), via atom transfer radical polymerization (ATRP). The film thickness and characteristic surface morphology were determined using ellipsometry and scanning force microscopy, respectively. The thickness and roughness of the resulting surfaces depend on the catalyst amount and the comonomer ratio, γ = [MAIGlc]0/[BIEM]0. A polymer brush of linear polyMAIGlc was also obtained in the presence of a sacrificial initiator via ATRP. Deprotection of the isopropylidene groups of the branched and linear polymer brushes resulted in hydrophilic surfaces as demonstrated by contact angle measurements. The quantitative deprotection was also confirmed by diffuse-reflectance infrared spectroscopy. X-ray photoelectron spectroscopy was further used to determine the surface chemical composition before and after deprotection.

The aim of this work was to establish and better understand the structure‐property relationship of fluorinated aromatic poly(ether imide)s (PEI) with respect to their electret performance. Therefore two series of PEIs with increasing fluorine content were synthesized. All PEIs are amorphous materials with glass transition temperatures above 220 °C. Thin films with thicknesses around 100 µm were compression molded and corona charged, and isothermal surface potential decay was investigated at 90 °C as an accelerated test for the electret performance. In comparison to the corresponding non‐fluorinated PEI, an improvement of up to thirty‐fold was achieved by the incorporation of trifluoromethyl moieties. Out of the investigated fluorinated PEIs, the polymer with the best charge storage performance maintained 87% of the initial surface potential charge after annealing at 90 °C for 24 h. It was also found that, within the investigated series, the highest fluorine content does not necessarily result in the best charge‐storage properties.magnified image

No abstract

The performance of a polymeric electret material depends on many parameters, and besides chemical structure, charging conditions, and application temperature, other factors, such as grade, manufacturer, processing history, and additive package, are critical. Commercial polyetherimide (PEI) Ultem V R 1000 films exhibited satisfying electret properties as revealed by an isothermal potential decay (ITPD) to 75% of the initial surface charge after 24 h at 90 C. It was found that after purification by reprecipitation this value drops to 34% and that the same PEI synthesized by two different methods revealed to be a very poor electret with charge retention of almost zero. Assuming that an additive in the commercial material might be responsible for this behavior, we identified an organophosphonite which is commonly used as antioxidant in high-temperature polymers. We incorporated this additive by melt compounding into purified PEI and found a dramatic increase in charge retention to 79% of the initial charge at an additive load level of 0.5 wt %. By immersing Ultem V R 1000 films in water, the electret behavior was further improved and almost 100% charge retention was achieved.