Silsesquioxanes: Novel compatibilizing agents for tuning the microstructure and properties of PLA/PCL immiscible blends

• Silsesquioxane proves to be efficient compatibilizing system for immiscible blends.
• Ad hoc synthesized POSS allows to improve the PLA/PCL blend morphology.
• The synthesized POSS allows to significantly reduce the amount of added copolymer.
• The synthesized POSS enhances the mechanical properties of the blend.

In this work, a novel and efficient approach for the compatibilization of poly(lactide) (PLA) and poly(ε-caprolactone) (PCL) immiscible blends, consisting in the addition of ad hoc functionalized polyhedral oligomeric silsesquioxane (POSS) molecules, was investigated. To this purpose, different kinds of POSS were exploited: one without specific functionalities (named POSS-oib) and another one characterized by hydroxyl groups (named POSS-OH) potentially capable of making the silsesquioxane compatible with both the polymer matrices. Moreover, in order to improve the silsesquioxane adhesion to the components of the blend, an amino-functionalized POSS was subjected to the grafting of a poly(ε-caprolactone)-b-poly(l-lactide) diblock copolymer (POSS-PCL-b-PLLA) by means of ring opening polymerization. The above silsesquioxanes were loaded into PLA/PCL blends through melt blending. SEM characterization showed that the POSS molecules are capable of modifying the blend morphology to different degrees. In particular, the synthesized POSS-PCL-b-PLLA nanohybrid proved very effective at ameliorating the compatibility of PLA/PCL blends by preventing the dispersed domains from coalescence, despite the small amount of silsesquioxane (2 wt.%), and consequently of diblock copolymer, added to PLA/PCL blend. The peculiar co-continous phase morphology, promoted at the interface by the presence of the above POSS, was found to enhance the mechanical properties of the blend, improving the elongation at break without reducing its Young’s modulus. Our study demonstrated that not only the microstructure but also the thermal properties of the blends were significantly affected by the presence of silsesquioxane molecules dispersed in the blend.

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