Developing high-performance fully biobased shape memory thermosets with a green strategy is a challenging topic of great interest. Herein, two unique fully biobased benzoxazine resins with excellent shape memory properties, denoted as poly­(IE-dea) and poly­(G-dea), were developed by synthesizing two fully biobased benzoxazine monomers (IE-dea and G-dea) using a solvent-free method. The thermal, mechanical, and shape memory properties of poly­(IE-dea) and poly­(G-dea) were studied. Among the fully biobased shape memory polymers reported so far, poly­(IE-dea) and poly­(G-dea) have the highest glass transition temperatures (138 and 216 °C), initial thermal decomposition temperatures (340 and 347 °C), and tensile strengths (85.1 ± 2.5 and 65.9 ± 2.7 MPa). In addition, poly­(IE-dea) and poly­(G-dea) exhibit excellent shape memory properties. After four shape memory cycles, their shape fixity ratios are 97.7–98.0% and 96.7–97.2%, respectively, and their shape recovery ratios are 96.7–97.2% and 93.0–93.4%. In fact, they are the first two fully neat biobased shape memory benzoxazine resins up-to-date. The mechanism behind the excellent integrated performances of poly­(IE-dea) and poly­(G-dea) results from unique integrated actions of the flexible decane segment and rigid cross-linked structure from the polymerization of oxazine rings.

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Two high-performance biobased benzoxazine resins from mono-phenols are developed with a green synthesis strategy.

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Oxazinium derivatives have recently played an important role in bioanalysis attributing to the distinguished properties, thus a detailed study of the structure-property relationship is especially significant. Herein, pH-sensitive optical properties of Nile Blue (1a), N-monoalkyl-Nile Blue (1b) and Azure A (1c) have been carried out in extreme acid and base conditions. Dyes 1a and 1c showed colorimetric changes by the protonation of nitrogen atom in strong acidic condition (pH < 2.0), and dyes 1a - c exhibited colorimetric changes by equilibrium between amino and imide groups in very strong basic case (pH > 7.6). Besides, their fluorescent properties were closed to ON - OFF and OFF - ON emissions at 640-820 nm under strong acidic and basic conditions. Moreover, the absorption and emission properties were reversible, and there were no remarkable optical intensity changes of dyes 1a - c under subacidic and neutral solutions (pH = 3.0-7.0). The (TD) DFT calculations were used to optimize the most stable structures of their corresponding protonated and deprotonated forms, and their absorption and emission properties were also explained. Their fluorescent properties nearly ON-OFF and OFF - ON in strong acidic and basic conditions at near-infrared region will give the possible application in pH detection for extreme conditions. Graphical abstract ᅟ.