Abstract: A process for preparing a functionalised polyolefin is described. The process comprises the step of reacting: (i) a polyolefin, (ii) a compound containing a functional group, and (iii) a coagent compound having Formula I: Xn—Y—Zm??(I) wherein: Y is a core moiety; Z is a moiety containing a carbon-carbon double bond or a carbon-carbon triple bond; X is a moiety different than Z and the bond between X and Y may be a single bond or a double bond; n is a whole number greater than or equal to 0; m is a whole number greater than or equal to 2; and m+n equals a number up to the valence of Y; wherein: (a) when m is 2 and n is 0, the process comprises initially reacting the polyolefin and the coagent to form a product that is then reacted with the compound containing the functional group, and (b) the compound containing a functional group is substantially inert in free radical-mediated polymerization reactions and in free radical-mediated grafting reactions.