Synthesis and characterization of copolyimides containing fluorine and silicon surface-modifying agents

Abstract

Understanding the effects that monomer chemistries have on material properties allows for fine tuning of polymer synthesis for current and future applications. In order to develop polymeric-based coatings that have minimal surface adhesion characteristics when exposed to a variety of contaminants, a more thorough understanding of fundamental structure–property relationships is needed. In the aeronautics field, one concept to improve fuel efficiency of future aircraft is to modify the wing design to enable laminar flow. There is a concern that contaminants such as insect residue and other debris will adhere to airflow surfaces and have sufficient height to disrupt laminar flow thereby increasing drag with concomitant loss of fuel efficiency. One potential solution would be a polymer surface or coating that prevents or minimizes adhesion of such contaminants. As part of a structure–property relationship study involving modification of surface properties, a series of copolyimides containing both fluorine and silicon surface-modifying agents (SMAs) were prepared and characterized. Based on knowledge of structure–property relationships with polyimides containing either type of SMA, it was hypothesized that the combination of two different SMAs may lead to unique surface properties as the two SMAs competed for surface area at the polymer–air interface. Copolyimides for this study were prepared through a multistep synthesis using an aromatic dianhydride with equimolar amounts of diamino functionalities comprised of an aromatic diamine along with two SMAs. Films were cast from copoly(amide acid) solutions that were subsequently thermally imidized under a nitrogen atmosphere. Polyimide films and coatings were characterized using differential scanning calorimetry, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, contact angle goniometry, scanning electron microscopy, and energy-dispersive X-ray spectroscopy to determine chemical, thermal, and surface properties. Select samples were subject to high velocity insect impacts in a small-scale wind tunnel and the resulting residues were characterized for height and surface area and compared to those of a control surface.