Elemental sulfur, a waste product of the oil refinement process, contains preformed dynamic Sulfur-Sulfur bonds promising to impart dynamicity onto polymers obtained from this monomer. Yet robust methodologies to access linear polymers with tuneable properties and functionality are rare. Addressing these problems, we here report a rare sequence selective terpolymerisation of elemental sulfur with aromatic thioanhydrides and epoxides under simple lithium alkoxide catalysis yields semi-aromatic Poly(ester-alt-Sx). This enables access to terpolymers from a greatly improved range of epoxide comonomers compared to previous methodologies, including industrially relevant, flexible, rigid, functional and natural product derived variants allowing to tune glass transition temperatures across a Tg range of >150°C. Mechanistic investigations reveal that the insertion of S8 leads to an unusual rate acceleration via coordinative participation of the polyester links sitting adjacent to the propagating chain-end. The thermal stability of the polymers allows for post polymerisation backbone modification via -S-S- bond metathesis. After crosslinking these can be applied as thermally reprocessable and acid degradable adhesives, the performance of which can be enhanced via backbone editing. Our contribution paves the way for the rational buildup of diverse and functional polymer structures from elemental sulfur waste enabled by mechanistic understanding.