4D printing of shape-programmable polymer-derived ceramics via two-stage folding-assisted pyrolysis strategy

Polymer-derived ceramics (PDCs) can be used in wide applications due to their high hardness and stable chemical properties. However, these characteristics lead to the challenging controllable deformation of additively manufactured PDCs. Herein, ultraviolet (UV)-curable polymer precursors were developed and a pyrolysis strategy was proposed. Through the two-stage folding-assisted pyrolysis strategy, the printed precursor can deform with programmable shape to attain 4D printing. Regardless of very low precursor ceramic yield (13.5 wt%), leading to a huge pyrolysis shrinkage (59.91%), the SiOC ceramics with dense, crack-free complex programmable shapes were successfully obtained. The working mechanism of the two-stage pyrolysis was explained by characterising and analysing the chemical bond status. The effects of unpyrolyzed, first-pyrolysed and second-pyrolysed samples on the skeleton shrinkage, weight loss, and mechanical properties were also studied and compared. The proposed strategy provides a feasible way for the preparation of PDCs with complex programmable shapes that are dense and crack-free by photopolymerization 4D printing.