The synthesis of precipitated silica having improved chemical and physical properties of use as a reinforcing filler in polymeric matrices is described. Improvements in the properties result from the synthesis of the silica al a reduced ionic strength. In particular, the use of silicia acid during synthesis, provides a solution of reduced ionic strength, which favors the formation of improved colloidal structure via increased aggregation and reduced agglomeration. In addition, the surface of the silica precipitate formed may be modified by the addition of surface modifying agents, during synthesis to further enhance the desired reinforcing properties of the precipitated silica. The invention also embodies polymeric compositions of improved tensile and elongation strengths, with the compositions including precipitated silica, synthesized at reduced ionic strengths and having modified surfaces, in combination with a polymeric compound.