Intercalative polymerization of cyclic esters in layered silicates: Thermal vs. catalytic activation

Poly(ε-caprolactone) layered silicate nanocomposites were synthesized by in situ intercalative ring-opening polymerization (ROP) of ε-caprolactone. The polymerization was promoted by thermal or catalytic initiation starting from either non-modified natural sodium-montmorillonite (MMT-Na) or montmorillonite modified by different ammonium cations bearing either non-functional alkyl chains or chains terminated by carboxylic acid or hydroxyl functions. The resulting compositions were analyzed by small-angle X-ray diffraction and transmission electron microscopy. The clay dispersion depended on the structure of the alkyl ammonium. Exfoliated nanocomposites were formed when hydroxyl-containing alkyl ammonium was used; otherwise, partially intercalated/partially exfoliated structures were observed. Moreover, owing to the inherent catalytic properties of the montmorillonite surface, it was also possible to prepare intercalated nanocomposites by in situ polymerization of ε-caprolactone in presence of non-modified montmorillonite-Na (MMT-Na) without any added catalyst.