Amphiphilic diblock copolymers were synthesized based on poly(2-ethyl-2-oxazoline) (PEtOz) as a hydrophilic block and aliphatic polyesters such as poly(l-lactide) (PLA) or poly(ε-caprolactone) (PCL) as a hydrophobic block. Their micellar characteristics in an aqueous phase were investigated by using dynamic light scattering and fluorescence techniques. The block copolymers formed micelles in the aqueous phase with critical micelle concentrations (cmcs) in the range of 1.0−8.1 mg/L. The cmc values become lower upon increasing the length of the hydrophobic block. The mean diameters of the micelles were in the range of 108−192 nm, with a narrow distribution. In general, the micelle size increased as the hydrophobic PLA or PCL block became larger. The partition equilibrium constants, K v, of pyrene in the micellar solutions of the block copolymers were from 1.79 × 105 to 5.88 × 105. For each block copolymer system of PEtOz−PLA or PEtOz−PCL, the K v value increased as the length of the hydrophobic block increased. The steady-state fluorescence anisotropy values (r) of 1,6-diphenyl-1,3,5-hexatriene (DPH) were 0.265−0.284 in PEtOz−PLA solution and 0.189−0.196 in PEtOz−PCL solution. The anisotropy values of PEtOz−PLAs were higher than those of PEtOz−PCLs. The anisotropy values were independent of the length of the hydrophobic block when the chemical structures of the hydrophobic blocks were identical. The micelles underwent hydrogen bonding at pH <3.5 with poly(acrylic acid), which produced polymer complex precipitates that could be reversibly dispersed as micelles at pH >3.8.

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Multiwalled carbon nanotubes (MWNT) were functionalized with poly(L-lactic acid) (PLLA) with different molecular weights using a "grafting to" technique. The oxidized MWNT (MWNT-COOH) were converted to the acyl-chloride-functionalized MWNT (MWNT-COCl) by treating them with thionyl chloride (SOCl2) and reacting them with PLLA to prepare the MWNT-g-PLLA. FTIR and Raman spectroscopy revealed that the PLLA was covalently attached to the MWNT, and the weight gain due to the functionalization was determined by thermogravimetric analyses (TGA). The Raman signals of the MWNT were greatly weakened as a result of the PLLA grafting. The morphology of the grafted PLLA was examined by using SEM and TEM. The amount of grafted PLLA depended on the molecular weight of the PLLA. The PLLA coated on the MWNT became thicker and more uniform with increasing PLLA molecular weight from 1000 to 3000. However, the amount of grafted PLLA became lower when the molecular weight of PLLA was further increased to 11,000 and 15,000, and the PLLA attached to the MWNT showed a squid leglike morphology forming blobs and leaving much of the MWNT surface bare.

Poly(L-lactide) (PLA) was melt-mixed with micrometer-sized and nanosized calcium carbonate (CaCO 3 ) particles before and after modification with calcium stearate. Adhesion between the CaCO 3 particles and the PLA matrix was assessed qualitatively by scanning electron microscopy observation of the fractured surface morphology of the composites. The effect of the incorporation of the CaCO 3 particles on the thermal stability of the PLA-based composites was quantified by the temperatures corresponding to 5 and 50% of weight loss and the activation energy determined through thermogravimetric analyses of the composites. The tensile strength and modulus values of the composite were improved greatly without a significant loss in the elongation at break when the nanosized CaCO 3 was incorporated up to 30 wt %.

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An organoclay containing epoxy groups, namely twice functionalized organoclay (TFC), was successfully synthesized by reacting (glycidoxypropyl)trimethoxysilane with Cloisite25A (C25A), which had previously been modified with an amine compound. The role of the epoxy groups on the clay surface in improving the morphology of the poly(l-lactide) (PLLA)/clay composites was investigated. The silicate layers in the PLLA/TFC composite were initially intercalated and became fully exfoliated as the epoxy content in the TFC was increased from 0 to 0.359 mmol/g, as confirmed by infrared spectra and TEM observations. However, the exfoliated morphology became an intercalated/exfoliated mixture when the clay content in the composites was in excess of 5 wt %. Not only was the tensile modulus and tensile strength enhanced by compounding with TFC but so was elongation at break of the PLLA. In contrast, the tensile properties of the PLLA/C25A were far inferior to those of the PLLA/TFC, and its elongation at break and tensile strength decreased sharply as the content of C25A increased. The higher degree of exfoliation in the silicate layers in PLLA/TFC and the improved mechanical properties compared with those of PLLA/C25A were attributed to the enhanced interfacial interaction through a chemical reaction between the epoxy groups of the TFC and the end groups of the PLLA.