Tunable photonic materials via monitoring step-growth polymerization kinetics by structural colors

The functional and responsive properties of elastomeric materials highly depend on crosslink density and molecular weight between crosslinks. However, tedious analytical steps are needed to obtain polymer network structure–property relationships. In this article, an in situ structure–property characterization method is reported by monitoring the structural color change in a photonic elastomeric material. The photonic materials are prepared in a two-step polymerization process. First, linear chain extension occurs via Michael addition. Second, photopolymerization ensures crosslinking, resulting in the formation of an elastomeric photonic network. During the first step, the step-growth polymer process can be monitored by following the photonic reflection band redshift, allowing to program the molecular weight between the crosslinks. During network formation, the crosslink density, chain length between crosslinks, and the colors are “frozen in.” These processes can be locally controlled creating both single-layered multicolor patterned and broadband reflective coatings at room temperature. The scalability of the coating process is further demonstrated by using a gravure printing technique. Additionally, the final coatings are made responsive toward specific solvents and temperature. Here the modulus, response, and color of the coating are controlled by tuning the crosslink density and molecular weight between crosslinks of the elastomeric material.