Avoiding Disulfides: Improvement of Initiation and End‐Capping Reactions in the Synthesis of Polysulfide Block Copolymers

Abstract

In episulfide polymerisation, the exchange between thiols and disulfides results in a chain transfer, which may compromise the control over molecular weight and molecular weight distribution. Self‐assemblable polysulfide structures have found promising applications as bionanomaterials (responsive nanoparticles or vesicles, surface films, etc.), but the necessary precise molecular control may indeed be jeopardised by the presence of disulfides. We here discuss in depth the role of disulfides as chain transfer agents and present some robust solutions, aiming at minimising the presence of disulfides and optimising synthetic procedures.

Controlled ring‐expansion polymerization of thiiranes based on cyclic aromatic thiourethane initiator

“…S2), and GPC measurement revealed a large M n of 160,000 and a broad M w / M n of 2.36. These results indicate that a typical ring‐opening polymerization of thiirane occurs, initiated by thiolate anion, which was presumably produced by the nucleophilic attack of chloride anion of TBAC on PPS. On the other hand, the large polymeric product obtained in the above control experiment was not observed in the REP in the presence of BT, indicating that the thiourethane structure based on the BT initiator effectively regulated the polymerization by trapping the thiolate anion intermediate (Intermediate I in Scheme ) to lead to an acyl‐transfer mechanism instead of the intrinsic ring‐opening polymerization of thiiranes.…”

Oxidation‐Responsive Materials: Biological Rationale, State of the Art, Multiple Responsiveness, and Open Issues

“…Other routes include the Michael‐type addition of thiol(ates) on acrylates, and the original polysulfide main synthetic method, the nucleophilic substitution on good leaving groups such as dihalides . B) In the anionic episulfide ROP, disulfides are efficient chain transfer agents through thiolate/disulfide exchange; since it is difficult to ensure the absence of disulfides during the polymerization, it is often advisable to conduct the latter in the presence of a reducing agent such as an aliphatic phosphine . Through a variety of end‐capping and polymer analogous reactions, it is possible to introduce the means for additional polymerizations: for example, ATRP or RAFT, producing linear block copolymers, or further episulfide ROP in the side chains; the latter, end‐capped with the thiol‐reactive poly(ethylene glycol) vinyl sulfone (PEG‐VS), yields combs with block copolymeric arms .…”

The synthesis of polymeric sulfides by reaction of dihaloalkanes with sodium sulfide

“…The solid was filtered and washed with diethyl ether (30 ml). The filtrates were combined and the solvent was removed under reduced pressure to give tetrahydrothiophene (11) in 75-78% yield. 1 …”

“…Other problems may also arise. For example, in the episulfide polymerization, the presence of disulfide impurities results in the poor control over molecular weight distribution; therefore, work carried out by Wang et al (11) was aimed at minimizing the presence of disulfides and optimizing synthesis procedures.…”