Methacrylamidoundecanoylbiphenyl monomer was synthesized from 11-aminoundecanoic acid, and X-ray diffraction showed that it exhibits only crystalline structures. Its radical polymerization, followed by n.m.r. and g.p.c., provided comb-like polymers and their macromolecular characteristics were determined. Their thermotropic behaviour was studied by X-ray diffraction and the X-ray information showed that they exhibit, as a function of temperature, an ordered, perpendicular, monolayer, smectic S-B1 phase and a disordered, perpendicular, monolayer, smectic S-A1 phase. Comparison with polyacrylamide polymers with the same side chains showed that, if the two types of polymers exhibit two smectic phases (an ordered and a disordered one), as a function of temperature, the nature of the main chains determines the types of smectic structures of the polymers. Polyacrylamide polymers exhibit two tilted bilayer smectic mesophases : S-I2 and S-C2, instead of the two perpendicular monolayer smectic phases S-B1 and S-A1 exhibited by polymethacrylamide polymers.