The copolymerization of 1-hexene with t-Bu2P(CH2)3CH=CH2 (1) or t-Bu2P(CH2)9CH=CH2 (2) has been achieved using CpMe2Ti(NPt-Bu3) as the precatalyst and B(C6F5)3, [Ph3C][B(C6F5)4], or [PhNMe2H][B(C6F5)4] as the activator. The resulting polymers are shown to incorporate up to 9% of the phosphine comonomer, albeit with reduced catalyst activity and polymer molecular mass. The cause of the catalyst inhibition is also considered in the light of phosphine–activator interactions.