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.