Low friction poly(amide-imide) coatings with silicones as tethered liquids

•PDMS, the most potent lubricant cannot be used directly within PAI coatings.•Covalent binding of PDMS to a PAI matrix during polymerization is performed.•The PDMS remains in a liquid-like state, i.e. “tethered liquids”.•Lubrication performance of tethered liquid on copper wires is investigated.•Increased performance, and no leeching of lubricant. In the production of enamelled copper wires, coated with the high-performance polymer PAI (poly(amide-imide)), friction between multiple polymer surfaces as well as between the polymer and the slot substrate are significant issues. These effects drastically reduce the achievable packing density of the wires, which directly correlates to efficiency of the products. Conventional methods of lubrication involve use of leeching lubricants or addition of wax layers, which in return produces other problems. Moreover, the most potent lubricant PDMS cannot be used due to incompatibilities with the PAI matrix. A desirable solution for these issues is the covalent attachment of lubricating substances, ideally PDMS, to the PAI matrix. To achieve this, block copolymers from PAI and PDMS of different shapes and block length distributions were synthesized and cured as coatings. It was found that, depending on the specific type of block copolymer, friction can be drastically reduced by up to one order of magnitude. This effect was observed in lab scale experiments as well as in industrially produced enamelled copper wires. AFM investigations furthermore revealed a surface structure with distinct PDMS domains, which show liquid-like behavior as well as strong covalent binding to the matrix. Several parameters of the domains can be fine-tuned by variation of block copolymer parameters.