Microphase\nSeparation Transformation in Bio-Based\nBenzoxazine/Phenolic/PEO‑<i>b</i>‑PCL Diblock\nCopolymer Mixtures Induced by Transesterification Reaction

Herein, we synthesized a difunctionalized bio-based vanillin\nazine\nmonomer (4,4′-((1<i>E</i>,1′<i>E</i>)-hydrazine-1,2-diylidenebis(methaneylylidene))bis(2-methoxyphenol),\nVBAZ-2OH) via a Schiff base reaction between vanillin and hydrazine\nmonohydride. Subsequently, we successfully prepared 2,2′-(((1<i>E</i>,1′<i>E</i>)-hydrazine-1,2-diylidenebis(methaneylylidene))bis(8-methoxy-2<i>H</i>-benzo[<i>e</i>][1,3]oxazine-6,3(4<i>H</i>)-diyl))bis(ethan-1-ol), VBAZ-BZ-2OH), which contains oxazine units,\nthrough a Mannich condensation reaction of VBAZ-2OH with ethanolamine\nand paraformaldehyde in 1,4-dioxane as the solvent. The chemical structures\nof these two monomers (VBAZ-2OH and VBAZ-BZ-2OH) were characterized\nby using NMR and FTIR analyses. Our study aimed to investigate the\ntransesterification reactions by blending different VBAZ-BZ-2OH/phenolic\nresin (BP) compositions with a PEO<sub>112</sub>-<i>b</i>-PCL<sub>99</sub> (EC) diblock copolymer to form various BP/EC blends.\nThese blends exhibit competitive hydrogen-bonding interaction phenomena,\nwhich were analyzed using one-dimensional and two-dimensional FTIR\nanalyses. Interestingly, after thermal treatment of BP/EC blends at\n150 °C, the ordered self-assembled lamellae or hexagonal packed\ncylinder structures transform into the disordered micelle or disorder\nstructure in BP/EC blends as a result of the transesterification reaction\ndue to EC becoming miscible with a VBAZ-BZ-2OH monomer, disrupting\nthe ordered self-assembled structure, which was confirmed through\nTEM and SAXS analyses. The transesterification reaction could easily\nunderstand the order–disorder morphological transformation\nusing BP/EC blends to replace thermogravimetric analysis (TGA) coupled\nwith microcomputed gas chromatography (TGA-GC) analyses.