Bisphenol A is the most important chemical for producing epoxy resins, but as of today is not bio-based accessible. Furthermore, it is rated as a substance of very high concern and possesses reproductive toxic and endocrine-disrupting properties. Phlorotannins, a class of polyphenols, are structurally highly suited for serving as sustainable bisphenol A alternatives. They are largely found in brown algae, which are already being harvested for alginate production. Phlorotannins thus represent a promising marine raw material for the chemical industry which otherwise has received little attention in research to date, at least in the field of epoxy resin formulation. For this study, an epoxy-resin model compound based on phloroglucin, the simplest phlorotannin, was chosen to gain insight into reactivity and thermo-mechanical characteristics. As curing agents, well-established systems for ambient-temperature cure, e.g. isophorone diamine, as well as anhydrides for heat cure were applied. In all cases, thermosets with glass transition temperatures higher than 100 ℃ could be obtained under cross-linking conditions comparable to today’s procedures. In the case of a phthalic acid anhydride derivative, even a Tg of 198 ℃ has been determined, proving the high potential of the cured systems for industrial usage, e.g. as impregnating resins for fiber-reinforced plastics.