Polypropylene has been grafted with pentabromobenzyl acrylate by reactive extrusion. The degree of grafting is about 4% by weight of the polypropylene independent of the weight of brominated monomer in the feed. Ungrafted monomer remains largely unreacted. Fibers spun from the grafted polypropylene display good mechanical properties and are easily dyed with anthraquinone type disperse dyes. The dyed cloths have good color stability even after laundering.