We investigate the aggregation behavior of oligomeric poly(1,4-phenylene)s in which each benzene ring of the backbone is 2,5-disubstituted with a hydrophobic (alkyl) and a hydrophilic (oxyethylene) side chain. This substitution scheme leads to amphiphilic polymers in which the boundary between the hydrophobic and hydrophilic segments is disposed parallel to the polymer backbone. The polymers are designated as PPP-CmE3(n(n)), where C-m = CmH2m+1 and E-3 = CH2(OC2H4)(3)OCH3 represent the side chains and n(n) is the mean degree of polymerization. Two polymers, PPP-C12E3(12) and PPP-C6E3(50), were studied. PPP-C6E3(50) forms a nematic lyotropic phase in toluene solutions. PPP-C12E3(12) forms a lamellar phase with a layer spacing of 5.7 nm in the pure state. The polymer can be solubilized in water by comicellization with low-molecular-weight nonionic surfactants such as C8E4. Cryogenic transmission electron microscopy reveals that PPP-C12E3(12) in the micellar solutions forms fiberlike aggregates of a length greater than 200 nm and a cross-sectional diameter of 5.9 nm. Monolayers of the two polymers spread at the water surface are studied by surface pressure (Pi-A) measurements and X-ray reflectometry. The Pi-A isotherms are reminiscent of those of the respective monomeric alkyl-ethoxylate amphiphiles but also reflect the influence of covalent bonding of the monomer entities in the polymer backbone.