Using POSS reagents to reduce hydrophobic character in polypropylene nanocomposites

Three POSS reagents (1,2-propanediolisobutyl POSS, glycidylisooctyl POSS, and triglycidylisobutyl POSS, all 5 wt%) are incorporated into a commercial isotactic polypropylene, PP. Infrared and Raman spectroscopy show that the blending has been successful as evidenced by the presence of Si-O-Si bands at 1098-1110 cm^-1, which are not present in the base polymer. The inclusion of 5 wt% of the various POSS reagents leads to a general increase in the loss modulus at the T_g (e.g. the greatest increase being from ca. 125 MPa to ca. 150 MPa) from DMTA data, although the T_g of the PP is slightly diminished by 4-8 K depending on the POSS used. The melting behaviour is also altered as the addition of POSS leads to a more diffuse and multimodal melting endotherm in the blends, although the melting temperature does increase slightly (7 K). TGA data confirm that the thermal and thermo-oxidative stability of PP is not adversely affected by the inclusion of the POSS reagents at this concentration. Tensile data show that the ultimate tensile strength (ca. 24.7 ± 0.1 MPa) remains the same, although the tensile modulus (ca. 1.24 ± 0.06 GPa) is reduced by up to 0.22 GPa and the maximum load does reduce by ca. 80-160 N. Contact angle measurements for the PP (99.72°± 0.73) show that the inclusion of the POSS reagents at this level does reduce its hydrophobic character as the greatest depression in contact angle is effected by the inclusion of 5 wt% triglycidylisobutyl-POSS (85.77°± 1.39). Molecular modelling and QSPR techniques are used to predict selected physical properties of the PP/POSS nanocomposites.