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 treatment of a waste plastics feedstock; (b) providing a hydrocarbon stream B; (c) supplying a feed C comprising a fraction of the hydrocarbon stream A and 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 2:: 800 and:::; 850° C., preferably 2:: 805 and:::; 835° C.; and •⋅ the weight ratio of steam to feed C is >0.3 and