Block Copolymer Nanoparticles
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The use of nanoscale objects is a way to enhance properties of materials in a wide range of fields because the small dimensions of the objects can be responsible for high specific surface or for quantum effects. Nanotechnology is consequently of great interest in electronic materials or biomedical applications. The challenge is to realize nanoscale systems with size and morphology control. In this context, our aim is to study the self-assembly of AB block copolymers containing two incompatible polymers to form nanoparticles in solution.
It has been known for many years that when AB block copolymers are dissolved in a solvent that is selective for one of the blocks, colloidal aggregates such as micelles can form as a result of the association of the insoluble blocks. When the insoluble A block is flexible, spherical micelles with an amorphous core are obtained, whereas if the A block is rigid, micelles with anisotropic shapes can result.
In this work, we study the formation of nanoparticles obtained in solution by cocrystallization of AB and A′B diblock copolymers, where the A and A′ blocks can cocrystallize. In a selective solvent (good for B and bad for A and A′), the mixture is expected to self-assemble in particles with a crystalline core (AA′) surrounded by a shell (B) swollen with the solvent.
This type of complex can be obtained by mixing optically active polymers with identical chemical structures but opposite optical configurations. Poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) are semicrystalline polymers that form a racemic crystal called stereocomplex. We have thus synthesized poly(l-lactide)–poly(ε-caprolactone) (PCL) and poly(d-lactide)–poly(ε-caprolactone) diblock copolymers and have studied their association in a good solvent for the poly(ε-caprolactone) block.