Controlled Polymer Grafting on Single Clay Nanoplatelets

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Abstract
We report on the controlled chemical grafting of well-defined polymer chains onto individual montmorillonite-type clay nanoplatelets and the direct visualization of the formed hybrid material at the nanoscale level. Our approach is based on the use of a surfactant mixture that contains varying proportions of hydroxyl-substituted alkylammonium and unsubstituted alkylammonium cations to exchange the initial Na+ counterions of the natural montmorillonite. This allows for the exchange of Na+ by a tunable amount of hydroxyl functions at the surface of the clays. Those functions are then derivatized into aluminum alkoxides in order to initiate the ring-opening polymerization of ε-caprolactone directly from the clay surface that was swollen in an organic solvent. Atomic force microscopy measurements on the resulting polymer-grafted nanoplatelets demonstrate the strong dependence of the coating of the individual clay particles with the composition of the surfactant mixture used for the cationic exchange. This allows for the generation of a range of morphologies varying from polymer islands distributed over the clay surface to homogeneous polymer layers thoroughly coating the platelets. Finally, the control that is achievable over the synthesis of this new family of organic−inorganic nanohybrid materials has been extended to the surface grafting of semicrystalline poly(ε-caprolactone)−poly(lactic acid) diblock copolymers with defined compositions.

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