Study of the material properties of periodic colored band structures in MAA-based frontal polymerization, focusing on microporosity, polycrystalline domains, and thermal responses

The study investigated the formation of colored polymer band structures via frontal polymerization (FP) in a reaction system comprising methacrylic acid (MAA), resorcinol, benzoyl peroxide (BPO), and N, N-dimethylaniline (DMA). The reaction was initiated by adding DMA, which generates free radicals and releases heat, thereby enabling the formation of solid-phase polymer fronts. The heat released during the reaction further promotes polymerization in adjacent layers, creating a feedback loop that facilitates the downward movement of the polymer fronts. Three distinct reaction zones were observed during the polymerization process, designated as non-crystalline (NC), unstable crystallization (UNS), and periodic band structures (PBs), which differed in crystallization features, textural properties, and morphologies. A model of chemical reactions has been presented to illustrate the chemistry of the FP reaction involving MAA and resorcinol monomers, and it was validated analytically using ¹ H and ¹³ C NMR spectra. The results indicated that the simultaneous production of two significant products, namely 2-hydroxy-7-methylnaphthalene-1,4-dione and Poly-3-methacrylic acid, 2-hydroxy, 1,4-naphthaquinone, during the FP reactions crystallizes periodically and forms colored polymer band structures. XRD analysis of polymerized materials indicates that they are polycrystalline, with distinct crystal properties. The d-spacing and peak positions have been measured and matched with the ICDD database. The surface area and porosity were measured using Brunauer-Emmett-Teller (BET) adsorption isotherms. The results revealed that the surface areas of the NC and PBs materials were 7.03546 m ² /g and 1.97483 m ² /g, respectively, with average pore sizes ranging from 2.08 to 3.18 nm. The differential thermal analysis (DTA) showed a high endothermic enthalpy of 4.63 kJ/g for the PBs materials, which indicates a high degree of crystallinity and strong interfacial binding.