Form-stable benzoxazine-urethane alloys for thermally reversible light scattering materials

Abstract

Thermally reversible light scattering (TRLS) materials based solely on benzoxazine-urethane (BA-a/PU) alloys were successfully fabricated and demonstrated in this work. The alloys displayed the opaque state below 40°C. The alloys were transformed to the transparent state upon exposing to the transition temperature of 60-130 °C, depending on the molecular weights and mass concentrations of urethane prepolymers in the BA-a/PU alloys. The optical state transitions were reversible with small hystereses. BA-a/PU alloys exhibited a good optical contrast with 0%T at the light scattering state and almost 100%T at the transparent state. The alloys were glassy and form-stable up to 250 °C, due to the synergistic behavior in the glass transition temperatures. The reaction-induced phase separation effectuated by the incorporation of urethane prepolymer into thermosetting polybenzoxazine, the sizes and local concentrations of the phase-separated urethane microdomains in the supporting polybenzoxazine matrix, and the reversible dissolution and demixing of urethane microdomains and polybenzoxazine phase played crucial roles on TRLS properties of the developed benzoxazine-urethane alloys.

Impact Response of Aramid Fabric-Reinforced Polybenzoxazine/Urethane Composites Containing Multiwalled Carbon Nanotubes Used as Support Panel in Hard Armor

“…The BA-a oxazine may undergo ring-opening at a suitable temperature, and the phenolic hydroxyl groups of the resulting product may then react with the isocyanate group of urethane prepolymer to form urethane carbonyl linkages in the copolymer networks. These results are also in good agreement with the previous reports by our group [ 38 , 39 ] and Takeichi et al [ 26 ] using different types of resins.…”

“…In addition, new absorption peaks at 878 cm −1 and 1477 cm −1 , consistent with a tetra-substituted arene, were observed, consistent with the ring-opening reaction as shown in Figure 3b [26,33]. A further indication of the ring-opening reaction was evident by the appearance of a broad signal at about 3380 cm −1 which was assigned to a phenol, a functional group that can react with the isocyanate group (NCO) of the urethane prepolymer [38,39]. The formation of networks between the BA-a monomer and the urethane prepolymer, both in virgin (unfilled) and filled (0.1 wt% MWCNT) forms, after thermal curing was also investigated by FT-IR spectroscopy; key results are shown in Figure 3c.…”

“…In addition, new absorption peaks at 878 cm −1 and 1477 cm −1 , consistent with a tetra-substituted arene, were observed, consistent with the ring-opening reaction as shown in Figure 3 b [ 26 , 33 ]. A further indication of the ring-opening reaction was evident by the appearance of a broad signal at about 3380 cm −1 which was assigned to a phenol, a functional group that can react with the isocyanate group (NCO) of the urethane prepolymer [ 38 , 39 ].…”

Fabrication of imprinted photonic films via predesigned multiple UV‐polymerizations and their ability to detect solvents and metal ions in aqueous solution

“…Among these materials, the CLC, which has a helical pitch, shows exceptional performance in optical physics. Because the unique helical structure has periodic characteristics, it can selectively reflect circularly polarized light according to Bragg's law 29–33 . The light reflection from a cholesteric helical structure is more complex than that from a crystal lattice, resulting in a more pronounced and obvious color change.…”

High Temperature Sensing and Detection for Cementitious Materials Using Manganese Violet Pigment

“…The materials, which were recently recognized to exhibit a distinct color change in response to change in temperature, are found in different forms, such as metal oxides, polymers, pigments, and leuco dyes. Reversible thermochromic materials are used in the applications of smart windows, ultra-thin films, temperature sensors, cool colored, and protective coatings [18][19][20][21][22][23][24][25][26]. The irreversible thermochromic materials experience a permanent color change at certain temperatures and are widely used in applications, such as aeronautical components, furnaces, damage warnings, and thermal flow sensors [27][28][29].…”