The alternating copolymerization of 3,3-dimethylallene with carbon monoxide was achieved using [Pd(PPh3)(2)(MeCN)(2)](BF4)(2) as the catalyst, The use of bidentate phosphines resulted in drastically reduced yields. In order to gain insight into the copolymerization mechanism, the stepwise successive insertions of 3,3-dimethylallene and carbon monoxide into palladium-carbon bonds in the complexes, Pd(PPh3)(2)(Me)(Cl), [Pd(PPh3)(2)(C(O)C6H4-Me-p)(MeCN)](BF4), and [Pd[(Dppp)(Me)(MeCN)](BF4) (Dppp: 1,3-bis(diphenylphosphino)propane), were studied. These studies, in turn, led to a novel living catalytic system which was used to synthesize a terpolymer with alt-allene-carbon monoxide and alt-ethene-carbon monoxide blocks.