Photopolymerizable thiol-ene composition was prepared as a mixture of PETMP and TTT with 1:1 stoichiometric ratio of thiol to ene functional groups, containing 1 wt. % of DMPA. The reason we chose cleavage photoinitiator is that it gives higher quantum yield for the production of reactive radicals as compared to the hydrogen-transfer photoinitiators [20 (link)]. Photoinitiator was dissolved in a warm PETMP at 60 °C in an amber glass jar, then the calculated amount of TTT was added avoiding the direct day or artificial light; components were thoroughly mixed with a spatula. The clear colorless viscous mixtures were applied on flexible polyethylene terephthalate (PET) substrates (APLI paper S.A., product Ref. 10580) as a 100 µm thick layer via the Meyer rod coating method. The PET substrate (thickness 0.1 mm) side was suitable for inkjet printing and was used in the deposition process. The water contact angle (CA) for this substrate side was determined to be 30 ± 1°, which is significantly lower than for polydopamine-coated (CA = 49.8°) or carboxyl-group-modified (CA = 50.6°) PET [33 (link)], but close to the O2 plasma treated PET films (CA = 34 ± 1°) [34 (link)]. In another instance, deposition was performed on the polytetrafluoroethylene (PTFE) plate. Samples were cured simultaneously at the intensity of 1.64 mW/cm2 (wavelength: 254 nm) and 0.8 mW/cm2 (wavelength: 365 nm). After that, cured network was obtained, denoted as PETMP-TTT. Free-standing PETMP-TTT films were obtained by gently peeling the film from the PTFE plate.
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