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