The present invention relates to a process for the production of propylene-based polymers from waste plastics feedstocks comprising the steps in this order of: (a) providing a hydrocarbon stream A obtained by hydrotreatment of a pyrolysis oil produced from a waste plastics feedstock; (b) optionally providing a hydrocarbon stream B; (c) supplying a feed C comprising a fraction of the hydrocarbon stream A and optionally a fraction of the hydrocarbon stream B to a thermal cracker furnace comprising cracking coil(s); (d) performing a thermal cracking operation in the presence of steam to obtain a cracked hydrocarbon stream D; (e) supplying the cracked hydrocarbon stream D to a separation unit; (f) performing a separation operation in the separation unit to obtain a product stream E comprising propylene; (g) supplying the product stream E to a polymerisation reactor; and (h) performing a polymerisation reaction in the polymerisation reactor to obtain an propylene-based polymer; wherein in step (d): • the coil outlet temperature is ≥800 and ≤850° C., preferably ≥805 and ≤835° C.; and • the weight ratio of steam to feed C is >0.3 and