Compositions, processes, and methods are provided relating to styrenic polymers, including high impact polystyrene (HIPS), also referred to as rubber-modified polystyrene. In one aspect, a process is provided for making high impact polystyrenes, comprising the steps of combining a monovinylarene component, a monovinylarene-conjugated diene block copolymer, and a conjugated diene polymer. In another aspect, the feed components form an emulsion having a continuous phase and a dispersed phase. The continuous phase comprises at least a portion of the monovinylarene component and at least a portion of the conjugated diene polymer. The dispersed phase is suspended within the continuous phase, and comprises globules having at least a portion of the monovinylarene-conjugated diene block copolymer, a remaining portion of the monovinylarene component, and a remaining portion of the conjugated diene polymer. The monovinylarene component is polymerized in the presence of the emulsion alone or in the presence of other feedstocks.