The co catalyst is initially contacted with {TAIL ~ either} of the transition metal catalyst or the electron donor for {HEAD ~ a first contact time} of 5 120 seconds 
The co catalyst is initially contacted with { TAIL ~ either } of the transition metal catalyst or the electron donor for { HEAD ~ a first contact time } of 5 120 seconds
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH