Nanocomposites composed of poly(ɛ-caprolactone) and oligocaprolactone-modified imogolite utilizing biomimetic chelating method

The imogolite modified with a catechol-terminated ε-caprolactone oligomer (CLO-imogolite) was synthesized by a biomimetic treatment of imogolite with 4-(hydroxyethylthioacetyl)catechol (HETAC) and subsequent ring-opening polymerization of ε-caprolactone (CL). The FT-IR analysis revealed that the catechol moieties certainly chelated to aluminum atoms on the surface of imogolite. The ¹H-NMR spectral analysis of the CLO-imogolite revealed that the oligomerization of CL certainly occurred. The organo-fraction of CLO-imogolite was evaluated to be 35.6 wt% from the thermogravimetric analysis. Poly(ε-caprolactone) (PCL)/CLO-imogolite nanocomposites prepared by a solution casting method were comprised of homogeneously dispersed nanotubes and some aggregated nanotubes. Crystallization temperature of PCL/CLO-imogolite slightly rose with increasing CLO-imogolite and the formed crystalline particles were slightly finer than those of pure PCL. Tensile strengths and moduli of PCL/CLO-imogolite nanocomposites increased with increasing CLO-imogolite contents. The PCL/CLO-imogolite 3 wt% exhibited the highest elongation at break and tensile toughness, which were much higher than those of pure PCL and PCL/imogolite 3 wt%.