The catalytic efficacy of trans-[(R3P)(2)Pd(O2CR')(LB)][B(C6F5)(4)] (1) (LB = Lewis base) and [(R3P)(2)Pd(K-2-O,O-O2CR')][B(C6F5)(4)] (2) for mass polymerization of 5-n-butyl-2-norbornene (Butyl-NB) was investigated. The nature of PR3 and LB in 1 and 2 are the most critical components influencing catalytic activity/latency for the mass polymerization of Butyl-NB. Further, it was shown that 1 is in general more latent than 2 in mass polymerization of Butyl-NB. 5-n-Decyl-2-norbornene (Decyl-NB) was subjected to solution polymerization in toluene at 63(+/- 3) degrees C in the presence of several of the aforementioned palladium complexes as catalysts and the polymers obtained were characterized by gel permeation chromatography. Cationic trans[(R3P)(2)PdMe(MeCN)][B(C6F5)(4)] ER = Cy (3a), and Pr-i (3b)] and trans-[(R3P)(2)PdH (MeCNA[B(C6F5)(4)] [R = Cy (4a), and Pr-i (4b)], possible products from thermolysis of trans-[(R3P)(2)Pd(O2CMe)(MeCN)][B(C6F5)(4)] ER = Cy (1a) and Pr-i (1g)], as well as trans-[(R3P)(2)Pd((eta(3)-C3H5)][B(C6F5)(4)] [R = Cy (5a), and Pr-i (5b)], were also examined as catalysts for solution polymerization of Decyl-NB. A maximum activity of 5360 kg/ (molPd h) of 2a was achieved at a Decyl-NB/Pd: 26,700 ratio which is slightly better than that achieved with 5a [activity: 5030 kg/(molPd h)] but far less compared with 4a [activity: 6110 kg/(molPd h)]. Polydispersity values indicate a single highly homogeneous character of the active catalyst species. (c) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 103-110, 2009