Compositions comprising an organic polymer as the matrix and inorganic particles as the filler and exhibiting in mixture a) 20 to 99.9% by wt. of an organic polymer and b) 0.1 to 80% by wt. of inorganic particles, where the sum of the constituents a) and b) amounts to 100% by wt.; and optionally c) 0 to 100 parts by weight of b) of various additives, in which case the content of the additives c) relates to the sum of a) and b), calculated as 100 parts by weight. characterized in that the composition can be obtained by incorporating particles and optionally other additives into the polymer matrix, in which case the particles to be incorporated i) are aggregates of globular primary particles; ii) the size of the primary particles is in a range of 0.5 nm to less than 100 nm; iii) the volume-weighted median value d50 of the particles is in a range of greater than 0.50 μm to 0.5 μm, determined by means of static light scattering; and iv) the inorganic particles are modified with functional groups, the inorganic particles exhibiting at least three types of functional groups of varying reactivity. The compositions can be prepared in a number of way, for example, by reprecipitation from the dissolved state or by mixing in an extruder and are used for preparing fibers, films and shaped articles with improved mechanical properties.