CF3SO3H was found to serve as a more superior initiator for the polymerization of diisopropenylbenzenes than the conventionally used acids such as H2SO4. Much faster polymerization at lower temperatures seems to be ascribed to the higher acidity of CF3SO3H. The use of microflow systems was also found to be effective in increasing the indane unit content, especially for 1,4-DPB. Fast mixing and uniformity of the temperature seem to be responsible. The thus-obtained polymers of high indane unit content serve as useful materials having high thermal resistance and low dielectric constants.