Using the LC-xPBE/6-311++G(d,p)//LC-omega PBE/6-311G(d,p) approach, we have computed the structures, the longitudinal electronic polarizabilities and second hyperpolarizabilities of polydiacetylene and polybutatriene oligomers of increasing size (up to 48 carbon atoms). It turns out that infinitely long polybutatriene chains are about 2.6 (3.3) more polarisable than the corresponding polyacetylene (polydiacetylene). The second hyperpolarizability of polybutatriene is 10 (25) times larger than for polyacetylene (polydiacetylene). Comparisons with previous Hartree-Fock and MP2 results are also carried out. (C) 2008 Elsevier B.V. All rights reserved.