Disulfide Polymer Research Articles

Tunable Q-switched fiber laser based on saturable edge-state absorption in few-layer molybdenum disulfide (MoS₂).

We fabricate a few-layer molybdenum disulfide (MoS₂) polymer composite saturable absorber by liquid-phase exfoliation, and use this to passively Q-switch an ytterbium-doped fiber laser, tunable from 1030 to 1070 nm. Self-starting Q-switching generates 2.88 μs pulses at 74 kHz repetition rate, with over 100 nJ pulse energy. We propose a mechanism, based on edge states within the bandgap, responsible for the wideband nonlinear optical absorption exhibited by our few-layer MoS₂ sample, despite operating at photon energies lower than the material bandgap.

Comparison of cyclic and polymeric disulfides as catalysts for the regioselective chlorination of phenols

Two cyclic and two polymeric disulfides have been synthesized and established to be useful catalysts for the chlorination of m-xylenol, o-cresol, m-cresol and phenol using freshly distilled sulfuryl chloride in the presence of aluminum or ferric chloride as a co-catalyst at room temperature. The yields of p-isomers and para/ortho ratios were higher compared to cases where no catalyst was used with most catalysts for most phenols even when a very low concentration of disulfide was used.

Main-chain sulphur containing water soluble poly(N-isopropylacrylamide-co-N,N′-dimethylacrylamide sulphide) copolymers via interfacial polycondensation

Here, we report the first synthesis of water soluble poly(N-isopropylacrylamide-co-N,N′-dimethylacrylamide sulfide) copolymers via conventional interfacial polycondensation method using phase transfer catalyst (PTC). The effect of various kinds of PTC having different aliphatic chain length and counter ion were employed to examine the kinetics of polysulfide polymer formation. The reactivity ratios, determined employing extended Kelene–Tüdös method using feed composition obtained from 1H NMR analysis, suggest that N-isopropylacrylamide (NIPAM) is more reactive than N,N′-dimethylacrylamide (DMA) in both mono- and di-sulfide polymers. Thermal transition behavior investigated by differential scanning calorimetry (DSC) demonstrated that as the sulphur rank of the sulfide main chain linkages increased, the flexibility of the polymers increased reflected by lower glass transition temperature (Tg) values. The thermal degradation behavior and the major degradation products have been characterized by thermogravimetric analysis (TGA) and electron-impact mass spectroscopy (EI-MS), respectively. Both the studies reveal that the degradation takes place due to weak-link scission of the polymeric main chain. Solubility in water and in most of the common organic solvents even after the sulphur rank increased from 1 to 2 in the main chain, is expected to render potential applications in biological field as well as in industry for these interesting new class of polymers.

PH-dependent sustained release characteristics of disulfide polymers prepared by simple thermal polymerization

Biocompatible polymers have played an integral role in the advancement of drug delivery systems. The discovery of a novel polymer with innovative properties can provide great opportunities to enhance drug efficacy as well as reduce side effects. In this study, a novel disulfide polymer was synthesized and characterized. Its monomer is alpha-lipoic acid (ALA), which is synthesized in all cells in the human body. The disulfide polymer was obtained by the simple thermal polymerization of crystalline particles at a temperature higher than its melting point, followed by precipitation purification. It had rubbery and sticky characteristics. In vitro release tests demonstrated that the disulfide polymer had both pH-dependent degradation and related sustained release profiles, with a degraded form of ALA. Therefore, this novel class of responsive polymers that can be prepared by simple thermal polymerization has pronounced potential to contribute to future drug delivery systems.

Synthesis and characterization of poly(methylene disulfide) and poly(ethylene disulfide) polymers in the presence of a phase transfer catalyst

Poly(methylene disulfide) and poly(ethylene disulfide) were synthesized from the polycondensation of methylene dichloride and ethylene dichloride monomers, respectively, in the presence of benzyltriethylammonium chloride as a phase transfer catalyst. The structures of the synthesized polysulfides were confirmed via the elemental analysis, attenuated total reflectance Fourier transform infrared spectroscopy and X-ray diffraction techniques. Moreover, the thermal behaviors of synthesized poly(methylene disulfide) and poly(ethylene disulfide) were characterized using differential scanning calorimetry and thermogravimetric analysis methods. The synthesized poly(methylene disulfide) and poly(ethylene disulfide) have molecular weights of about 2262 and 2863 g/mol, respectively. In addition, the polymers have crystalline structures absorbed in the amorphous sections. However, the d-spacing of polymers’ crystalline parts was different. Moreover, poly(methylene disulfide) and poly(ethylene disulfide) have a two- and one-step degradation behavior, respectively.

Green Polymer Chemistry: Living Dithiol Polymerization via Cyclic Intermediates

This paper reports the synthesis and characterization of disulfide polymers obtained by oxidation of 2-[2-(2-sulfanylethoxy)ethoxy]ethanethiol (DODT) using a benign, synergistic system comprised of air, dilute hydrogen peroxide and triethylamine as a catalyst that can be recycled. The dn/dc value of the polymer in THF was determined to obtain absolute molecular weight measurements. High molecular weight disulfide polymers (up to M(n) = 250000 g/mol) with polydispersity indices as low as M(w)/M(n) = 1.15 were obtained. Thermal analysis by DSC and TGA demonstrated that the rubbery polymers had a T(g) of -50 °C and began to degrade at 250 °C. Dithiothreitol reduced the polymers back to the original monomeric units in 33 h. MALDI-ToF showed the involvement of oligodisulfide rings (2-14 mers) in the polymerization that displayed the characteristics of a living/controlled polymerization; poly(DODT) was readily chain extended with 1,2-ethanedithiol. The chain extension indicates a class of living polymerization which is governed by radical recombination.

Synthesis of a Functional Metal-Chelating Polymer and Steps toward Quantitative Mass Cytometry Bioassays

We describe the synthesis and characterization of metal-chelating polymers with a degree of polymerization of 67 and 79, high diethylenetriaminepentaacetic acid (DTPA) functionality, M(w)/M(n) ≤ 1.17, and a maleimide as an orthogonal functional group for conjugation to antibodies. The polymeric disulfide form of the DP(n) = 79 DTPA polymer was analyzed by thermogravimetric analysis to determine moisture and sodium-ion content and by isothermal titration calorimetry (ITC) to determine the Gd(3+) binding capacity. These results showed each chain binds 68 ± 7 Gd(3+) per chain. Secondary goat antimouse IgG was covalently labeled with the maleimide form of the DTPA polymer (DP(n) = 79) carrying (159)Tb. Conventional ICPMS analysis of this conjugate showed each antibody carried an average of 161 ± 4 (159)Tb atoms. This result was combined with the ITC result to show there are an average of 2.4 ± 0.3 polymer chains attached to each antibody. Eleven monoclonal primary antibodies were labeled with different lanthanide isotopes using the same labeling methodology. Single cell analysis of whole umbilical cord blood stained with a mixture of 11 metal-tagged antibodies was performed by mass cytometry.

Properties of Thiol End‐Capped and Iodine‐Doped Sexithiophene Disulfide Semiconducting Polymers Bridging Nanogap Gold Electrodes

Doped photoresponsive nanodevices. A thiol end-capped and iodine-doped sexithiophene disulfide polymer is used to bridge nanogap gold electrodes via an in-situ oxidation, doping, and self-assembly method. Temperature-dependent semiconducting and photoresponsive nanodevices are formed and Coulomb-blockade phenomena are observed in these organic molecule-based nanodevices.

Synthesis of a Pyridyl Disulfide End-Functionalized Glycopolymer for Conjugation to Biomolecules and Patterning on Gold Surfaces

A pyridyl disulfide end-functionalized polymer with N-acetyl-d-glucosamine pendant side-chains was synthesized by atom transfer radical polymerization (ATRP). The glycopolymer was prepared from a pyridyl disulfide initiator catalyzed by a Cu(I)/Cu(II)/2,2'-bipyridine system in a mixture of methanol and water at 30 degrees C. The final polymer had a number-average molecular weight (M(n)) of 13.0 kDa determined by (1)H NMR spectroscopy and a narrow polydispersity index (1.12) determined by gel permeation chromatography (GPC). The pyridyl disulfide end-group was then utilized to conjugate the glycopolymer to a double-stranded short interfering RNA (siRNA). Characterization of the glycopolymer-siRNA by polyacrylamide gel electrophoresis (PAGE) showed 97% conjugation. The activated disulfide polymer was also patterned on gold via microcontact printing. The pyridyl disulfide allowed for ready immobilization of the glycopolymer into 200 microm sized features on the surface.

The nucleophilic, phosphine-catalyzed thiol–ene click reaction and convergent star synthesis with RAFT-prepared homopolymers

The synthesis of 3-arm star polymers from reversible addition–fragmentation chain transfer (RAFT)-prepared precursor homopolymers in combination with thiol–ene click chemistry is described. Homopolymers of n-butyl acrylate and N,N-diethylacrylamide were prepared with 1-cyano-1-methylethyl dithiobenzoate and 2,2′-azobis(2-methylpropionitrile) yielding materials with polydispersity indices (Mw/Mn)≤1.18 and controlled molecular weights as determined by a combination of NMR spectroscopy, size exclusion chromatography (SEC), and matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Subsequent one-pot reaction of homopolymer, hexylamine (HexAM), dimethylphenylphosphine (DMPP), and trimethylolpropane triacrylate (TMPTA) results in cleavage of the thiocarbonylthiol end-group (by HexAM) of the homopolymer yielding a macromolecular thiol that undergoes DMPP-initiated thiol-Michael addition to TMPTA yielding 3-arm star polymers. The presence of DMPP is demonstrated to serve an important second role in effectively suppressing the presence of any polymeric disulfide as determined by SEC. Such phosphine-mediated thiol–ene reactions are shown to be extremely rapid, as verified by a combination of FTIR and NMR spectroscopies, with complete consumption of the CC bonds occurring in a matter of min. MALDI-TOF MS and SEC were used to verify the formation of 3-arm stars. A broadening in the molecular weight distribution (Mw/Mn∼1.35) was observed by SEC that was attributed to the presence of residual homopolymer and possibly 2-arm stars formed from trimethylolpropane diacrylate impurity. Interestingly, the MALDI analysis also indicated the presence of 1- and 2-arm species most likely formed from the fragmentation of the parent 3-arm star during analysis. Finally, a control experiment verified that the consumption of CC bonds does not occur via a radical pathway.

Alkylphenol Disulfide Polymer Accelerators and the Vulcanization of Isobutylene Based Elastomers

Abstract Vulcanization of isobutylene/isoprene copolymer (butyl rubber) using sulfur and organic accelerators is facilitated by the presence of the carbon-carbon double bond in the copolymer isoprenyl unit. The low number of unsaturated monomer units, usually in the order of 2%, has traditionally necessitated use of ultra-fast accelerators such as tetramethyl thiuram disulfide (TMTD) or zinc dimethyldithiocarbamate (ZMDC). Use of such accelerators can result in formation of nitrosamines which may be undesirable. There are a number of alternatives to thiuram and dithiocarbamate cure systems such as use of xanthates and phosphate based accelerators. Alkylphenol disulfide based accelerators also enable attainment of favorable properties when used in butyl and halobutyl compounds. Use of alkylphenol disulfide accelerators in butyl rubber compounds can allow improvement in reversion resistance, adhesion to natural rubber tire casing compounds, and aged property retention. In bromobutyl compounds containing alkylphenol disulfide accelerators in binary (two accelerators) or tertiary (three accelerators) cure systems, adjustment in cure rate to meet specific requirements and aged property retention is possible. This, fifth in a series of studies on the vulcanization of isobutylene elastomers, explores the use of alkylphenol disulfide cure systems for vulcanization of both butyl and bromobutyl rubbers and is intended to provide a starting point for further development work.

A Biodegradable pH-sensitive Micelle System for Targeting Acidic Solid Tumors

A new pH-sensitive micelle delivery system based on TAT cell penetrating peptide and biodegradable sulfonamide grafted disulfide polymer is presented. The system consists of two components: (1) A polymeric micelle made of Poly(L-lactic acid)-b-poly(ethylene glycol) (PLLA-b-PEG) conjugated to TAT (TAT-micelle), (2) A pH-sensitive diblock copolymer (poly(L-cystine bisamide-g-sulfadiazine))-b-PEG (PCBS-b-PEG). The anionic PCBS complexed with cationic TAT of TAT-micelles forms the final carrier. PCBS showed rapid degradation in the presence of cysteine. The TAT-micelles showed increase in particle size between pH 8.0 and 7.0 upon mixing with PCBS-b-PEG indicating complexation. As the pH was further decreased (pH 6.8 to 6.0) two populations were observed, one of normal TAT-micelles and the other of aggregated PCBS-b-PEG. Flow cytometry showed significantly higher uptake of TAT-micelles at pH 6.6 indicating deshielding compared to pH 7.4. The anticancer drug doxorubicin (DOX) was encapsulated into the TAT-micelles, and the in vitro cytotoxicity at different pHs was evaluated. The system was able to distinguish pHs 7.2 and 7.0 in terms of cytotoxicity.

4-Amino- 4H-1,2,4-triazole-3,5-dithiol: A Modifiable Organosulfur Compound as a High-Energy Cathode for Lithium-Ion Rechargeable Batteries

We have studied the electrochemistry of the organosulfur compound, 4-amino--1,2,4-triazole-3,5-dithiol (ATAD), as a potential cathode electroactive material for lithium-ion rechargeable batteries. The redox behavior was investigated via cyclic voltammetry, and the charge-transfer kinetics of ATAD were compared to those of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) and thiophene-2,5-bis(thiolate) (TBT). The redox reactions of ATAD were ascribed to the thiol groups at the 2 and 5 positions, forming a disulfide polymer during oxidation and cleaving the disulfide bonds during reduction. In addition to its chemical tunablity via the amine group, an important feature that DMcT does not possess, ATAD exhibited comparable charge-transfer kinetics to DMcT. Moreover, the charge-transfer kinetics of ATAD were significantly greater than those of TBT, which possesses chemically tunable points. These results point to the importance of heteroatoms adjacent to the thiolate groups to obtain fast charge-transfer kinetics. Furthermore, it was revealed that the redox reactions of ATAD could be accelerated by the conducting polymer poly(3,4-ethylenedioxythiophene). The chemical tunability of ATAD and the fast charge-transfer kinetics, as well as the high positive potential of the redox reactions, could enable the practical use of this organosulfur compound as a charge-storage material in lithium-ion rechargeable batteries.

Demonstration of Galvanically Stimulated Release of a Corrosion Inhibitor: Basis for “Smart” Corrosion Inhibiting Materials

Galvanic reduction of an oxidatively formed disulfide polymer of 2,5-dimercapto-1,3,4-thiadiazole (polyDMcT) in a conducting carbon paste releases its monomer anion in neutral NaCl. The monomer anion exhibits very good oxygen reduction reaction (ORR) inhibition at Cu cathodes. Coupling a carbon paste containing polyDMcT to a freshly polished metallic Al surface releases a corrosion inhibiting reduction product from the paste that can diffuse to and inhibit a remote cathode. This chemistry forms the basis for a “smart” corrosion inhibiting material that will release an ORR inhibitor when a corrosive environment couples the material to a base metal as would be the case for a coating with a defect. No release would occur in the absence of either the reducing force of the base metal, or the presence of a coupling ionic (corrosive) environment.

Polyanthra[1,9,8-b,c,d,e][4,10,5-b,c,d,e]bis-[1,6,6a(6a-S) trithia]pentalene-active material for cathode of lithium secondary battery with unusually high specific capacity

Polyanthra[1,9,8-b,c,d,e][4,10,5-b,c,d,e]bis-[1,6,6a(6a-S)trithia]pentalene (PABTP) was prepared and investigated as cathode active material for lithium secondary batteries. The organic disulfide polymer was prepared by the direct sulfurization of anthracene and the oxidative coupling polymerization of the sulfide anthracene, characterized by FT-IR, Raman, elemental analysis, XPS and XRD. The polymer was used as cathode active material and the lithium secondary batteries were assembled and tested. The polymer had high specific capacity up to 1500 mAh g −1, which remained the value of 800 mAh g −1 at the 77th cycle, and kept high charge–discharge efficiency of 85% in the whole test.

Fluorescent Labeling of RAFT-Generated Poly(N-isopropylacrylamide) via a Facile Maleimide−Thiol Coupling Reaction

We report a facile labeling technique in which the telechelic thiocarbonylthio functionality of well-defined poly(N-isopropylacrylamide) (PNIPAM) prepared by room temperature RAFT polymerization is first converted to the thiol and subsequently reacted with a maleimido-functional fluorescent dye, N-(1-pyrene)maleimide (PM). Nearly monodisperse PNIPAM (M(n) = 39 500 g/mol, M(w)/M(n) = 1.07) was synthesized using a trithiocarbonate-based CTA, 2-dodecylsulfanylthiocarbonylsulfanyl-2-methyl propionic acid (DMP), and a conventional azo-initiator, namely, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70), as the primary source of radicals. The key to successful conjugation of PM to PNIPAM is the implementation of a two-step reduction process involving (1) the cleavage of the trithiocarbonate with a strong reducing agent, in this case, NaBH4, to form a mixture of polymeric thiols and disulfides and (2) the conjugation of PM to the pure polymeric thiol in the presence of tris(2-carboxyethyl)phosphine.HCl (TCEP). We show that TCEP efficiently eliminates the formation of polymeric disulfides and thus allows for the desired addition of the free polymeric thiol across the maleimide double bond. This concept is demonstrated using SEC-MALLS and UV-vis spectroscopy measurements.

Aromatic disulfide polymers back to macrocyclic disulfide oligomers via cyclo-depolymerization reaction

A brand new and highly efficient method has been developed for the synthesis of aromatic macrocyclic disulfide oligomers. Cyclization was achieved by cyclo-depolymerization (CDP) of aromatic disulfide polymer in the presence of catalytic amount of thiols and weak base. The cyclic oligomers undergo a facile free-radical ring-opening polymerization to form high molecular weight polymer. Comparing with the conventional method for the preparation of macrocyclic aromatic oligomers by catalytic oxidation of dithiols, highly dilute condition was not necessary using the new method. The macrocyclics in high yield and with narrow molecular weight distribution were obtained. This method also provides a convenient technology for the recycle of aromatic disulfide polymers. ▪

Novel Synthesis of Macrocyclic Aromatic Disulfide Oligomers by Cyclodepolymerization of Aromatic Disulfide Polymers

Novel Synthesis of Macrocyclic Aromatic Disulfide Oligomers by Cyclodepolymerization of Aromatic Disulfide Polymers

A rewritable image formation by photopolymerization of trithiocyanuric acid

A photoinduced electron transfer system involving the tris(2,2 ′-bipyridyl)ruthenium complex, methylviologen and trithiocyanuric acid was constructed and used to induce a disulfide polymer on the electrode photochemically. Since the resulting polymer on the electrode can be depolymerized electrochemically, this system can be used for rewritable image formation. Furthermore, it was found that positively charged molecules were immobilized on the electrode by electrostatic bonding with the deprotonated mercapto groups on the disulfide polymer. These results indicate that a marked patterning of positively charged functional molecules on the disulfide polymer is possible using this photopolymerization system.

Direct evidence of redox mediation between a poly(aniline-co-N-propanesulfonic acid aniline) and 2,5-dimercapto-1,3,4-thiadiazole by UV-visible reflectance spectroscopy

A UV-visible reflectance and transmission spectroelectrochemical study of the redox behavior of thin films of a sulfonated polyaniline derivative, poly(aniline-co-N-propanesulfonic acid aniline) (PAPSAH) and of a mixture of this same derivative and 2,5-dimercapto-1,3,4-thiadiazole (DMcT) is reported. The study shows the differential spectral changes that accompany the oxidation of PAPSAH, which comprise increases in the polaron band at 400 nm and a band at 600 nm. The reduction process of PAPSAH, comprises decreases in these same spectral bands. These changes are shown to be reversible with potential. For the case of the PAPSAH/DMcT mixed film, the data also reveal spectral changes that are characteristic of oxidation of DMcT to produce a disulfide polymer during PAPSAH oxidation. These changes are also reversible with potential. These data represent the first direct, spectroscopic observation of the redox mediation between a polyaniline derivative and DMcT.