Endex hydrocarbon resins are made from purified aromatic monomers selected to produce a resin with an unusually high glass transition temperature and softening point. Due to these unique properties Endex resins are especially suited for use as modifiers for the end-blocks of styrenic block copolymers. Since Endex resins have a higher glass transition temperature and softening point than styrene they act to reinforce compounds based on block copolymers, giving them higher cohesive strength and resistance to high temperatures. Endex hydrocarbon resins are water-white in color and extremely stable against thermal and oxidative degradation. Since Endex resins associate only with the non-elastic styrenic portions of a block copolymer they normally do not impart tack properties.