Positron lifetime spectra were measured for a set of mixed alkanes with the same average carbon chain length but varying width of distribution (up to nine components). The range of rotator phase is broadening with the number of components; also the range of coexistence rotator - rigid crystal increases substantially when the distribution exceeds five components. With broadening of the component distribution the positronium formation on trapped excess electrons at low temperatures becomes less effective, and at nine components it disappears. (C) 2012 Elsevier B.V. All rights reserved.