Role of thiol‐disulfide exchange in episulfide polymerization

Abstract

Episulfide polymerization offers a number of features that are uncommon in other ring‐opening anionic mechanisms. Besides the negligible sensitivity to water, the most distinctive and novel one is likely to be the role of disulfides, which may act both at the levels of chain transfer and end‐capping, producing polymers that feature both terminal and internal disulfides. In this article, we have qualitatively studied the kinetics of chain transfer and measured the thiolate–disulfide exchange equilibrium constants. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2233–2249, 2008

Polymers and Sulfur: what are Organic Polysulfides Good For? Preparative Strategies and Biological Applications

“…The advantage of sulfur‐based initiators, such as thiols or dithiocarboxylates, either used as salts or deprotonated in situ, are a) to provide an initiation rate similar to the propagation one, b) to show a reasonably selective reactivity towards episulfides, and, c) to require only a mildly basic environment (p K a at most 9–10; i.e., total deprotonation achieved by a pH 11), therefore tolerating a large number of chemical functions. On the other hand, they have a significant drawback from the generally uncontrolled presence of disulfides, which can act as chain transfer agents,121 an effect originally pointed out by Marvel122 (Scheme ). As a result, thioacyl structures (thioacetates, thiocarbonates, thiocarbamates, etc.)…”

“… Summary of some important features of the anionic ring‐opening polymerisation of episulfides. Thiolates of large organic cations – “naked” thiolates – are the most effective species in terms of the propagation rate; in order to minimise the problems arising from the possible presence of disulfides (which exchange their organic residues with those of thiolates121), the initiators can be produced in situ from protected/masked thiols. …”

Oxidant‐Dependent REDOX Responsiveness of Polysulfides

“…Polysulfide preparative chemistry is overwhelmingly based on the living anionic polymerization of episulfides,17 which allows the preparation of narrow dispersity macromolecules with an excellent control over terminal groups,18 possibly featuring a blocky structure 19–21. Episulfide polymerization can be carried out under mild conditions, and can be performed in protic media,22 provided that disulfide impurities are removed 23, 24. This versatility has allowed to produce a variety of oxidation‐sensitive colloidal carriers based on poly(propylene sulfide) (PPS): vesicles13 and micelles,25 which are based on the self‐assembly in water of amphiphilic block copolymer structures, and nanoparticles,14, 26 which are produced through in situ emulsion polymerization techniques.…”

Synthesis of well‐defined and end‐polymerizable star‐shaped polysulfides and their application to negative photoresist

“…Size exclusion chromatography analysis (SEC) of polymers were performed using THF at a flow rate of 1.0 mL/min at 40 C using a system consisting of a Viscotek triple detector [refractive index, right angle laser light scattering (RALLS), and differential pressure] model 302 and an Asahi Techneion pump unit AT-2002 equipped with polystyrene gel tandem columns (Tosoh, TSKgel G1000H HR , G2500H HR , and G4000H HR ) after calibration with standard polystyrene samples (Tosoh). 1 H NMR (620 or 400 MHz) and 13 C NMR (154 MHz) spectra of the polymers were measured in CDCl 3 containing 0.03 vol % tetramethylsilane (Acros organics, 99.8%D) on JEOL model JNM-A620 or JNM-ECX400 spectrometer. Infrared spectra of polymers were measured by attenuated total reflectance (ATR) method on a Perkin Elmer SYSTEM2000 FTIR spectrometer equipped with a SensIR Technologies DuraSampl/IR 2 TM ATR unit (scans ¼ 10, resolution ¼ 4 cm À1 , and interval ¼ 1.0 cm À1 ).…”

“…For example, thiols, which can be useful monomers or initiators, are sensitive to oxidation by air, radicals, nucleophiles, and electrophiles. [12][13][14] Multifunctional thiols are especially susceptible to be oxidized to disulfides by oxidation under air, and keeping their purity is very difficult. 15,16 Controlled polymerization of episulfides is one of the most investigated methods for the synthesis of sulfur-containing polymers with well-defined structures and desired molecular weights.…”