TMP-based hyperbranched polyurethane elastomer (HBPUE) packaging material applied to anodic bonding

In this work, hyperbranched polyurethane elastomer (HBPUE) electrolyte and aluminum foil (Al) were joined together by anodic bonding. It provides a possibility for packaging of flexible devices to use anodic bonding. The HBPUEs were designed and prepared via prepolymerization method cured at room temperature using polypropylene glycol (PPG), toluene-2,4-diisocyanate(TDI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and the varying ratios of trimethylolpropane (TMP)/1,4-butanediol (BDO). All HBPUEs prepared exhibited low glass transition temperature (Tg) and good thermal stability. The highly branched structures increase the proportion of amorphous phase of HBPUEs, resulting in a high ionic conductivity with a highest value of 2.38 × 10−4 S cm−1 at 70 °C when adding TMP and BDO at the ratio of 0.45:0.45 (HBPUE3). There are no obvious diffraction peaks of the LiTFSI in the XRD patterns, indicating that LiTFSI was dissolved in polyurethane matrix completely. XRD results show that the structures of PEO-PUEs are amorphous. The HBPUEs prepared have good mechanical properties that can be used as packaging material. After bonded, the microstructures of the bonded interface between HBPUE and Al with a clear intermediate bonding layer could be observed by the cross-sectional scanning electron microscopy (SEM) images, and the elements diffused were also detected by the energy-dispersive spectrometer (EDS), indicating that the HBPUEs and Al were bonded together successfully. The maximum tensile strength for HBPUE3/Al was up to 1.15 MPa. All results demonstrated that the HBPUEs prepared would be a promising packaging material for flexible devices applied to anodic bonding.