Biodegradable “Core–Shell” Rubber Nanoparticles and Their Toughening of Poly(lactides)

Poly­(lactide) (PLA) nanocomposites were fabricated by solution blending of commercial poly­(l-lactide) (PLLA) and biodegradable core–shell particles, in which the core–shell particles were synthesized via octa polyhedral oligomeric silsesquioxane (octaPOSS)-initiated ring-opening copolymerization of a mixture of ε-caprolactone and l-lactide to form poly­(ε-caprolactone-co-lactide) (PCLLA) as rubbery core, followed by polymerization of d-lactide to form poly­(d-lactide) (PDLA) as outer shell. The outer PDLA layer could facilitate strong interactions between core–shell rubber particles and PLLA matrix via formation of stereocomplex. The randomness of PCLLA and the subsequent grafting of PDLA were monitored using nuclear magnetic resonance (NMR). The rubbery characteristic of PCLLA was confirmed by differential scanning calorimetry (DSC) which showed a T_g of ∼−7 °C. Stereocomplexation between PLLA and POSS-rubber-D was confirmed using Fourier transform infrared spectroscopy (FT-IR), DSC, and X-ray diffraction (XRD). The resulting biodegradable nanocomposites exhibit a 10-fold increase in elongation at break while maintaining other mechanical properties such as Young’s modulus and tensile strength. XRD, light scattering, scanning electron microscope (SEM), and thermogravimetric analysis (TGA) studies suggested that strong stereocomplex matrix/rubber interactions, good particle dispersion, rubber-initiated crazing, and low rubber content are the possible mechanisms behind such significant enhancements.