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