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 elon-gation at break, undergo controlled degradation, and support func-tional 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 tempera-ture-triggered shape change. The segmented thermoplastic polyes-ters (STEPs) can additionally be processed using melt-extrusion print-ing into 3D objects, thus opening potential application opportunities in the fabrication of implantable/degradable electronics, smart tex-tiles, and packaging.