Copolymerization of ethylene and divinyl formal by [{kappa(2)-P,O-(2-MeOC6H4)(2)PC6H4SO3}PdMe(dmso)] (1) by a coordination insertion mechanism affords highly linear polyethylenes with a high (12.5 mol %) incorporation of divinyl formal. This significantly exceeds the thus far relatively low incorporation (6:9 mol %) and activity with vinyl ether monomer in insertion polymerization. The resulting ethylene divinyl formal copolymers exclusively (>98%) contain five-membered (trans-1,3-dioxolane) and six-membered (cis-/trans-1,3-dioxane) cyclic acetal units in the main chain, and also in the initiating ends of this functionalized polyethylene. Comprehensive NMR analysis of the microstructure of these copolymers revealed that under pressure reactor conditions consecutive 2,1-1,2-insertion of divinyl formal into a Pd-H bond is preferred, but consecutive 1,2-1,2-insertion of divinyl formal into more bulky Pd-alkyls (growing polymer chain) is favored. Moreover, homopolymerization of divinyl formal yielded a non-cross linking poly(divinyl formal) with degrees of polymerization of DPn approximate to 26.