Synthesis of highly end-functionalized polyethylene chains was accomplished using both coordination chemistry and radical mediated thiol-ene chemistry. A vinyl end-terminated polyethylene (M-n, = 1440 g.mol(-1), PDI = 1.8) with a functionalization rate of 100% was synthesized using a P,O-chelated catalyst [Ni{Ph2PC(COOEt)=C(C6H5)O}Ph(PPh3)]. Thiol-ene reactions; were subsequently undertaken between vinyl-terminated polyethylene and the thiol-containing molecules thioglycolic acid, 2-mercaptoethanol, 1-thioglycerol, chloropropanethiol, and methyl thioglycolate. A range of end-functionalized polyethylenes was thus prepared using simple reaction conditions and exhibiting degrees of functionalization higher than 93%.