||As a synthetic method for C-C main chain polymers, polymerization of diazoacetates has attracted attention recently. We have found that Pd-based initiating systems, such as (NHC)Pd/borate and allylPdCl-based systems, are capable of giving relatively high Mn polymers with poor to moderate stereoselectivity. In addition, the allylPdCl-based system conducts the polymerization of diazoacetates with a bulky ester substituent such as cyclotriphosphazene, in a controlled manner with respect to Mn, giving polymers with a low polydispersity index (PDI) and block copolymers with a well-defined block sequence. The most important structural characteristics of the resulting poly(alkoxycarbonylmethylene)s is that the ester substituents are densely accumulated around the C-C polymer main chain because all the main chain carbon atoms have the substituents. Introduction of a variety of functional groups into the ester substituent could lead to development of a new type of functional polymeric materials, which will exhibit unique properties derived from the above-described accumulation of the functional groups.