A polyHIPE is a cross-linked, porous polymer synthesized through polymerization in the external phase of a high internal phase emulsion (HIPE). Crystalline polyHIPE polymers were synthesized through copolymerization of stearyl acrylate and divinylbenzene (DVB). Polymerizations initiated at the water/organic interface were compared to equivalent bulk polymers, to equivalent polymerizations initiated in the organic phase, and to model copolymers containing an equivalent non-cross-linking comonomer (styrene). The higher of the two main melting endotherms was related to a more ordered crystalline structure formed by stearyl acrylate-rich molecular segments that are preferentially synthesized by initiation at the interface. Cross-linking restricts molecular mobility, tying the polymer backbones together and reducing the peak temperatures and crystallinities. The decrease in modulus with increasing DVB content for the more crystalline polyHIPE reflects the dominant effect of crystallinity. The increase in modulus with increasing DVB content for the less crystalline polyHIPE reflects the dominant effects of cross-linking and polymer backbone stiffness.