Transparent, thermoplastic, aliphatic polyesters through crystallization under molecular confinement

In semi-crystalline biodegradable polymers, uncontrolled evolution of crystallinity impacts processing and bulk properties, limiting their application. Through molecular confinement of low-molecular-weight poly(L-lactic acid) (PLLA) segments by polysiloxane blocks and processing at far-from-equilibrium conditions, PLLA crystallization into lamellae of a few nm in thickness with coherence lengths below 100 nm was achieved, thus giving access to films that are optically transparent for over 5 years, possess high Young’s modulus and elongation at break, undergo controlled degradation, and support functional endothelialization. The films possess a nanophase segregated bulk morphology with a hydrophobic siloxane-dominated surface that can be pressure bonded following cold oxygen plasma activation and low-temperature glassy PLLA domains interspersed by nanoscale crystalline physical crosslinks that enable glass transition temperature-triggered shape change. The segmented thermoplastic polyesters (STEPs) can additionally be processed using melt-extrusion printing into 3D objects, thus opening potential application opportunities in the fabrication of implantable/degradable electronics, smart textiles, and packaging.