Synthesis of poly(L-lactide)-functionalized multiwalled carbon nanotubes by ring-opening polymerization

MWNTs are modified to possess hydroxy groups and are used as coinitiators to polymerize L-lactide by the surface-initiated ring-opening polymerization. FT-IR and TEM observations reveal that the PLLA is covalently attached to the MWNTs (MWNT-g-PLLA), and the weight gain as a result of the functionalization is determined by TGA analysis. Two kinds of solvents, namely DMF and toluene, are used to carry out the two series of polymerizations at 140 and 70 degrees C, respectively, for 2-20 h. The amount of grafted PLLA increases with the reaction time either in DMF or in toluene, but it increases more significantly in DMF at 140 than in toluene at 70 degrees C, with the reaction time being the same. The grafted PLLA layer on the MWNT is more uniform when the reaction is performed in DMF than in toluene, and some bare surfaces are observed in the TEM image of the MWNT-g-PLLA prepared in toluene. The MWNT-g-PLLAs are well dispersed in the organic solvents as well as in the PLLA matrix. Incorporation of MWNT-g-PLLA greatly improves the tensile modulus and strength without a significant loss of the elongation at break. The specific interaction between the MWNT-g-PLLA and the polymer matrix is quantified by way of the Flory-Huggins interaction parameter, B, which is determined by combining the melting point depression and the binary interaction model.