a method for preparing a surface - modified calcium carbonate useful in the synthesis of polyesters such as polyethylene terephthalate , polybutylene terephthalate , etc . to improve the polymer &# 39 ; s friction coefficient , which method comprises the step of forming a dispersion comprising calcium carbonate particles and a bi - functional reagent having two functional linking substituents consisting of a first substituent linking to the calcium carbonate particles and a second substituent which can link to the polyester , thereby bonding the calcium carbonate to the polyester through the bifunctional linking reagent ; and surface - modified calcium carbonate and polyesters containing same .