The invention provides intimate physical mixtures of macrocyclic polyester oligomer (MPO) and filler, as well as methods for their preparation and use. Improved dispersion of filler in a polymer matrix is achieved upon polymerization, and larger amounts of filler with high aspect ratio can be used. In one aspect, the invention provides mixtures of MPO with magnesium silicate. In another aspect, the invention provides a mixture of MPO, filler, and polymerization catalyst as a one-part, ready-to-polymerize material with a long shelf life. The one-part material can be used, for example, in the manufacture of parts without modification of existing processing equipment.