Polymer Grafted Nanoparticles in Polymer Matrices: Surface Chemistry and Stability

Polystyrene (PS) grafted silica nanoparticles (PS-g-NP) were synthesized and blended with PS matrices in order to study the conditions which lead to well dispersed particles or phase separated aggregates. During the synthesis of these particles we observed that by controlling the size of the atom transfer radical polymerization (ATRP) initiator on the particle surface the graft density of the PS chains could be controlled. In order to improve the control over the graft density we synthesized an ATRP initiator and an inert analog containing an amide group. Reacting mixtures of these two components to the particle surface was shown to lead to phase separation between the two components, which was confirmed using FTIR studies. This phase separation is caused by self-assembly of the amide containing inert analog in solution.;The graft density of the PS-g-NP's was varied from 0.1 to 0.7 chains/nm 2 and these particles were placed in PS matrices such that the ratio of matrix molecular weight (P) to grafted molecular weight (N) ranged from 0.6 to 7.7. The autophobic transition was scaled with respect to the graft density and P/N and compared to predictions made by scaling theory, where a weaker dependence on P was observed compared to predicted values. Interpenetration between the grafted and matrix chains was studied with differential scanning calorimetry and we observed that the matrix must be completely expelled from the grafted chains in order for phase separation to occur. Finally the impact of particle size on the phase diagram for PS-g-NP's in polymer matrices was studied, along with the impact of graft density on the rheological properties of the composite materials.