For modern applications in microoptics, the refractive index (n) of polymers can be adjusted in a certain range by the addition of electron-rich organic dopants. As an unwanted side effect, a pronounced plasticizing occurs. In this work, the addition of a crosslinker (divinylbenzene) to an unsaturated polyester matrix, doped with phenanthrene for n adjustment, allowed us to successfully suppress the plasticizing effect measured after polymerization. Even at high phenanthrene concentrations, the glass-transition temperature of the initial polymer could be almost retained. An increase of the polymer n from 1.5684 to a value of 1.6425 was achieved. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 3514-3519, 2011