Two-photon-induced thiol-ene polymerization as a fabrication tool for flexible optical waveguides

Abstract

In this contribution, we present two flexible thiol-ene-based hybrid materials based on epoxy and acetoxy polysiloxane matrix materials. The latter cross-linking mechanisms allow for orthogonal curing of the matrix in the presence of thiol-ene monomers enabling fast one-step access to two-photon-polymerization (2PP) curable substrates for waveguide fabrication. Another time-saving feature of our concept is the straightforward UV-flood-curing after 2PP, which is also a progress compared to previous works with elaborate postprocessing. Optimization of the ratio of thiol/ene moieties with respect to reactivity and analyses of the thermal stability of the materials, which is required for the industrial process, were carried out. Besides investigations regarding the refractive index of the materials, the proof of principle for successful waveguiding will be given. Flexible optical waveguides were successfully fabricated inside a low refractive polysiloxane matrix material.

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“…Thus, these vinyl-bearing species would be incorporated into the photopolymers to form a single polymer mesh. To avoid this unwanted interaction, we restricted the secondary network to condensation silicones, which do not participate in photochemistry, as previously demonstrated 20 . The Mold Max (MM) Series (Reynolds Advanced Materials) are commercially available silicones with industrially relevant strength, elongation, and toughness over a range of elastic moduli (250 kPa < E < 2 MPa).…”

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“…[133,134] Importantly, thiol-ene free-radical addition polymerization has several advantages over traditional radical reactions, including increased material homogeneity and low shrinkage, which makes it an attractive chemistry to be used in vat polymerization [135,136] and 2PP lithography applications. [137][138][139][140] Furthermore due to the nature of interaction between thiol groups and oxygen, whereby oxygen tends to abstract the hydrogen from a thiol group to regenerate the thiyl radical and thus allows continued polymerization renders this reaction not as susceptible to oxygen inhibition compared to traditional free radical chain growth mechanisms. [123,141] This is a positive attribute when considering crosslinking mechanism to be employed using top-down vat polymerization.…”