Head-to-head regioregular poly(p-phenylene)s (PPPs) were synthesized via Ni(O)-catalyzed polymerization of 2,2’-disubstituted 4,4’-bis[(methylsulfonyl)oxy]biphenyls (9). The corresponding regioirregular PPPs were prepared by the Ni(O)-catalyzed homopolymerization of 2-substituted 1,4-bis[(methylsulfonyl)oxy]benzenes (6) and by copolymerization of 6 with 9. The precursors of 6 and 9, i.e., 2-substituted 1,4-dihydroxybenzene (5) and 2,2’-disubstituted 4,4’-dihydroxybiphenyl (8), were synthesized by a synthetic method elaborated previously in our laboratory [J. Org. Chem. 1995, 60, 1066]. Head-to-head regioregular PPPs are crystalline and insoluble (except when the substituent is 4-tert-butylbenzoyl) while the corresponding regioirregular polymers are noncrystalline and soluble. The highest molecular weight regioirregular PPP was obtained by copolymerization of a 1:1 ratio of 6 with the corresponding 9. The influence of the size and the electronic properties of the substituent on the reactivity of monomers 6 and 9 and on the molecular weight of the regioirregular PPP is discussed. The highest molecular weight (M(n) = 34 790, corresponding to 176 phenylene groups relative to polystyrene standards) regioirregular PPP was obtained with a 4-fluorobenzoyl substituent. Fluorine both influences the reactivity of the leaving group and acts as more than one substituent since the hydrogen(s) ortho to it is (are) acidic.