Influence of Primary Structure on Responsiveness. Oxidative, Thermal, and Thermo-Oxidative Responses in Polysulfides

Using polymers with a double stimulus responsiveness, we show that primary structure, in addition to chemical composition, can significantly influence the response. This, however, applies to a stimulus of supramolecular nature (temperature) and not to a molecular one (oxidation). In the anionic ring-opening copolymerization of ethylene sulfide (ES) and propylene sulfide (PS), ES polymerizes faster and yields polysulfide chains with a gradient in composition; this primary structure can be varied by modifying the mode of monomer addition. Polysulfides with different primary structures (length of ES sequences) were linked to poly(ethylene glycol) (PEG) in amphiphilic block copolymers, whose (micellar) aggregates in water showed responsiveness to oxidants (solubilization) and gelation upon heating, similar to Pluronics. Both phenomena depended on composition (ES content), but only the second was affected by primary structure (the length of ES sequences), which was attributed to the influence of the latter on supramolecular aggregation.