Relationship between pore structure and H-1-NMR relaxation times in TiO2/poly(dimethylsiloxane) and CaCO3/poly(dimethylsiloxane) composite powders

Titanium(IV) oxide/polydimethylsiloxane (PDMS) and calcium carbonate/ PDMS composite powders were obtained by adsorption of the polymer from a chlorof orm solution onto the inorganic particles followed by a thermal treatment. The composites were characterized by H-1-NMR relaxation and porosimetry. Th e composites present shorter spin-lattice (T-1) and spin-spin (T-2) proton relaxation times than silica-reinforced PDMS, and the activation energies f or the motions that cause spin-lattice relaxation are 5.8, 4.9, and 0.72 kJ mol(-1) for TiO2/PDMS, CaCO3/PDMS, and neat PDMS, respectively, revealing the greater rigidity of the polymer chains within the composite. Spin-spin relaxation (T-2) measurements of the composites showed a major component wi th a shorter T-2 and a minor component with a longer T-2. The intensity rat io of these two components is very close to the ratio between the amount of polymer that remains between the particles and that penetrating the partic le pores as measured by Hg intrusion porosimetry. The shorter T-2 component was thus assigned to polymer interspersed among the particles, while the l onger T-2 component was assigned to polymer within the particle pores. (C) 1999 John Wiley & Sons, Inc.