Mechanistic aspects of palladium-catalyzed insertion copolymerizations of ethylene and R-olefins with methyl acrylate to give high molar mass polymers are described. Complexes [(N∧N)Pd(CH2)3C(O)OMe]BAr′4 (2) or [(N∧N)Pd(CH3)(L)]BAr′4 (1: L ) OEt2; 3: L t NCMe; 4: L t NCAr′) (N∧N ≡ ArNdC(R)-C(R)dNAr, e.g., Ar t 2,6-C6H3(i-Pr)2, R t H (a), Me (b); Ar′ t 3,5-C6H3(CF3)2) with bulky substituted R-di...