Facile method for fabricating atomic oxygen resistant polyimide films with excellent optical homogeneity containing hyperbranched polysiloxane

Abstract

Mechanically robust optical homogeneous polyimide (PI) films with desirable atomic oxygen (AO) erosion duration were fabricated by initially synthesizing amine-functionalized hyperbranched polysiloxane (NH2-HBPSi), then reinforcing the pristine polyimide skeleton with it via copolycondensation reactions. NH2-HBPSi macromolecule imparts desirable AO survivability to the resulting hybrids. The mass loss per unit area of hybrid films had a downward trend with rising NH2-HBPSi content and AO dose before the complete silica protective layer was formed. It has been proven by the experiments in an underground simulated AO environment. It decreased to 1% of that of pristine polyimide when NH2-HBPSi accounted for 30% of the solid content after 24 h AO attack. The stable thickness uniformity that can meet the Rayleigh criterion was achieved in a 30 wt% HBPSi PI film, mainly due to the selection of the best process parameters. Meanwhile, 30 wt% HBPSi PI demonstrates satisfactory mechanical properties, with a tensile strength of 228.9 MPa and elongation at break of 7.3%. The characterization of scanning electron microscopy confirmed that pristine polyimide was substantially eroded after AO exposure while the surface morphology of 30 wt% HBPSi polyimide showed no evident change. The low AO erosion yield and prominent film thickness uniformity may find extensive usage in ultra-lightweight space diffractive optical elements (DOE) working in low earth orbit (LEO).