The substrate was then immersed in water for 10 min to hydrate the GMO/HEA film and measured again under water for 60 sec and 3 frames (reported as fully hydrated condition). A GISAXS sample chamber with Kapton windows at the beam entry and exit and a thickness (transmission length) of 3 mm was used to measure the thin film underwater. The wafer was fixed to the bottom of the cell and covered with water. Finally, the milli-Q water was replaced by a solution containing 0.1 wt% of LAP initiator in milli-Q water and exposed to UV light. The 2D GISAXS patterns were acquired during HEA polymerization for 30 min (30 sec measurement with 30 sec delay between the frames). The GISAXS detector was a Pilatus3 1M (Dectris, Baden, Switzerland) with an active area of 169 × 179 mm 2 and a pixel size of 172 μm. The 2D GISAXS patterns were radially integrated into one-dimensional scattering curves I(q). GIXSGUI (Matlab-based software) simulated the space group and alignment of hydrated and polymerized films. For cubic space groups, unit cells with dimensions a = b = c and angles α = β = γ = 90° were used. The distortedwave Born approximation was applied as the incident angles exceeded the critical angle to the extent that effects from refraction from the water/film interface and diffraction from the reflected beam were negligible 2.5. Polymer Analysis. Gel permeation chromatography (GPC) was performed on an Agilent 1260 Infinity II HPLC system equipped with one Agilent PolarGel M guard column (particle size = 8 μm) and two Agilent PolarGel M columns (ID = 7.5 mm, L = 300 mm, particle size = 8 μm).