Cycloaliphatic epoxy-functionalized polysiloxanes for UV-mask 3D printing via cationic photopolymerization

Abstract

Cationic photocuring resins for UV-mask 3D printing exhibit lower volume shrinkage and higher printing accuracy compared to conventional free radical photocuring resins. However, their application is still hindered by low photoreactivity at 405 nm wavelength, with most improvements focusing on the development of novel photoinitiators. Herein, a synergistic strategy combining highly reactive cycloaliphatic epoxy groups with polysiloxane chains is proposed to develop novel cationic photocurable resins. Both cycloaliphatic epoxy-functionalized branched polysiloxane (CE-BSi) and linear polysiloxane (CE-LSi) are synthesized. Photocuring kinetics reveal that these resins exhibit significantly higher polymerization conversion (80 %), faster rate (25 s⁻¹), and shorter gelation time (4 s) than conventional cationic photocuring resins. They are successfully used to fabricate different geometric objects via UV-mask 3D printing technology. The 3D printed objects show a maximum tensile strength of 21 MPa, minimum volume shrinkage of 0.2 %, and outstanding thermostability (5 % weight loss temperature of above 395 °C, heat deflection temperature exceeding 100 °C). Theoretical simulations and experimental results indicate that the enhanced photoreactivity is primarily attributed to the high reactivity of cycloaliphatic epoxy groups and the superior molecular mobility of polysiloxane chains. This strategy successfully enables UV-mask 3D printing via a pure cationic photopolymerization mechanism, producing 3D objects with low curing shrinkage and excellent thermostability, thereby significantly expanding the potential applications of photocuring 3D printing technology.