Small core of piperazine/silane aggregation initiate efficient charring flame retardant effect in polypropylene composites

•Novel N/Si-macromolecules with varied aggregated core were synthesized.•Small core skeleton initiate charring flame retardancy with APP.•The aggregated structure of charring groups achieved an aggregation-charring effect.•Aggregation-charring effect strengthened flame retardancy of IFR in PP.