Producing high comonomer content propylene-based polymers

A process of producing a propylene-based polymer, the process comprising contacting, under copolymerization conditions, (A) propylene, butene and optionally ethylene, in a fluidized-bed reactor, the reactor containing (B) a fluidized bed comprising propylene-based polymer product particles and a catalyst, the propylene-based polymer having a seal initiation temperature (SIT) of 75° C. to 110° C., the process conducted under copolymerization conditions comprising a reactor temperature that is 20° C. to 40° C. less than the SIT of the propylene-based polymer;

• and wherein the catalyst comprises (1) a Ziegler-Natta pro-catalyst composition, (2) a co-catalyst, and (3) a mixed external electron donor (M-EED) system comprising (a) an activity limiting agent, and (b) a selectivity control agent, the process having a propylene partial pressure in a range of 80% to 120% of the maximum partial pressure, PPC3_max, as determined by the following equation:
• PPC3_max=625−43.7Et−20.0Bt−2.2T
• where Et, the ethylene content in the propylene-based polymer, is in a range of 0 to 2.5 wt %,
• Bt, the butene content in the propylene-based polymer, is in a range of 8 to 20 wt %, and where (2*Et+Bt) is less than or equal to 21 wt %, and T is the reactor temperature with a unit of ° C., and the partial pressure is with a unit of psi.