Cyclic‐poly(phthalaldehyde) (cPPHA) exhibits photo‐triggerable depolymerization on‐demand for applications like the photolithography of microfabricated electronics. However, cPPHA is inherently brittle and thermally sensitive; both of these properties limit its usefulness as an engineering plastic. Prior to this report, small molecule plasticizers are added to cPPHA‐based films to make the polymer more flexible. But plasticizers can eventually leach out of cPPHA, then leaving it increasingly more brittle throughout product lifetime. In this research, a new approach to fabricating flexible cPPHA blends for use as spun fibers is achieved through the incorporation of poly (ε‐caprolactone) (PCL) by a modified wet spinning method. Among blend compositions, the 50/50 cPPHA/PCL fiber shows fast transience (<50 s) in response to daylight while retaining the flexibility of PCL and mechanical properties of an elastomer (i.e., tensile strength of ≈8 MPa, Young's modulus of ≈118 MPa, and elongation at break of ≈190%). Embedding 2 wt% gold nanoparticles to cPPHA can further improve the transience rate of fibers comprising less than 50% cPPHA. These flexible, daylight‐triggerable cPPHA/PCL fibers can be applied to an extensive range of applications, such as wearable electronics, intelligent textiles, and zero waste packaging for which modest mechanical performance and fast transience are desired.

Fabrication of geometric structures through self-assembly of block copolymers normally requires complicated synthesis steps. Herein, we introduce a simple approach to prepare polymeric supramolecular microstructures through non-covalent self-assembly induced by host−guest co-crystallization assisted with ultrasound oscillation. Inclusion compounds formed between poly(ε-caprolactone)s (PCLs) and urea molecules in the ultrasound field were confirmed by FTIR, DSC, and X-ray diffraction. Homogeneous microscale particles and platelets with significant geometric structures were observed by SEM. Interestingly, instead of sophisticated techniques, the morphologies of inclusion compounds can be converted from particles to platelets by simply changing the guest polymer molecular weights due to their distinct crystal growth habits. Other parameters including guest polymer concentrations, ultrasound temperatures, powers, and mixing methods, which affect the size, shape, and uniformity of inclusion compound particles, were also studied. Considering the abundance of possible inclusion compounds formed between polymer guests and small molecule hosts, we believe that the understanding gleaned in this work will open a novel avenue for the design and the construction of polymeric supramolecular complexes.