Functional o-phthalaldehyde copolymers achieved via thermal cationic polymerization toward versatile acid degradable material platform

초록

We demonstrate the synthesis of acid-degradable copolymers via cationic copolymerization of o-phthalaldehyde (oPHA) with various monomers using a thermally latent initiator. Systematic exploration of different comonomer types, additives, and feed compositions enables copolymerization even at temperatures above the inherent ceiling temperature of poly(oPHA). Among explored comonomers, epoxide monomers are introduced as representative comonomers to impart and tailor the chemical functionalities, stability, and physical properties of the copolymers. Lactone monomers can also be incorporated into the oPHA-based copolymers only in the presence of epoxide comonomers. Cationic copolymerization at elevated temperatures not only enables the incorporation of monomers that cannot be copolymerized under low-temperature conditions, but also minimizes the formation of consecutive acetal repeating units that compromise thermal stability. Importantly, the acid-triggered degradability of the copolymers is fully preserved, despite the introduction of the comonomers. The degradability of the acetal groups in the poly(oPHA) units, combined with the reactive functionalities (e.g., vinyl and epoxide groups) of the comonomers, enables photoinduced crosslinking under UV illumination. This provides capabilities for the formation of degradable crosslinked networks and the selective formation of either positive- or negative-tone photopatterns. These results highlight the significance of the present design strategy to obtain degradable functional materials with structural stability, tunability, and reactivity through thermal cationic polymerization. Furthermore, the applicability of this platform to next-generation photopatterning systems and its underlying design principles will inspire the development of advanced stimuli-responsive and functional polymer materials.

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