Short carbon fiber reinforced aromatic polydisulfide derived from cyclic (4,4′‐oxybis(benzene)disulfide) via ring‐opening polymerization

Morphology, mechanical and thermal properties of short carbon fiber reinforced poly(arylene disulfide) synthesized by ring‐opening reaction of cyclic(arylene disulfide) oligomers were studied. These macrocyclic oligomers were prepared from 4,4′‐oxybis(benzenethiol) by oxidation coupling cyclization. Ring‐opening polymerization (ROP) was carried out by in situ melt molding in air. Oxidation reaction during the ROP was detected using the Raman spectrum technique. Three‐point bending tests were performed to determine the flexural properties of neat polymers and the composites. The results showed that the flexural strength and modulus of poly(arylene disulfide)/carbon fiber composites were greatly enhanced with the carbon fiber addition. The maximum weight loss peak temperatures of the composites increased with increasing short carbon fiber content. Good adhesion between carbon fiber and the matrix was observed using scanning electron microscopy (SEM) technique. Copyright © 2005 John Wiley & Sons, Ltd.     

Synthesis and ring‐opening polymerization of co‐cyclic(aromatic aliphatic disulfide) oligomers

An effective approach was presented for the synthesis of co‐cyclic(aromatic aliphatic disulfide) oligomers by catalytic oxidation of aromatic and aliphatic dithiols with oxygen in the presence of a copper‐amine catalyst. The aromatic dithiols can be 4,4′‐oxybis(benzenethiol), 4,4′‐diphenyl dithiol, 4,4′‐diphenylsulfone dithiol. The aliphatic dithiols can be 1,2‐ethanedithiol, 2,3‐butanedithiol, 1,6‐hexane dithiol. The co‐cyclic(aromatic aliphatic disulfide) oligomers were characterized by gradient HPLC, MALDI‐TOF‐MS, GPC, ¹H‐NMR, TGA, and DSC techniques. The glass transition temperatures of these co‐cyclics ranged from ?11.3 to 56.6°C. In general, these co‐cyclic(aromatic aliphatic disulfide) oligomers are soluble in common organic solvents, such as CHCl₃, THF, DMF, DMAc. These co‐cyclic oligomers readily underwent free radical ring‐opening polymerization in the melt at 180°C, producing linear, tough and high molecular weight poly(aromatic aliphatic disulfide)s. The glass transition temperatures of these polymers ranged from ?3.7 to 107.8°C that are higher than those of corresponding co‐cyclics. Copyright © 2003 John Wiley & Sons, Ltd.     

SYNTHESIS, CHARACTERIZATION AND RING-OPENING POLYMERIZATION OF CYCLIC (ARYLENE PHOSPHONATE) OLIGOMERS

INTRODUCTIONThe use of cyclic oligomers as macrocyclic precursors for the preparation of high performance polymers byring-opening polymerization (ROP) has sparked much interest in recent years. It could produce a revolutionarychange in the preparation of advanced composite materials, and is of great importance in the polymerizationprocess yielding polymers such as the reinforced reactive injection model (RRIM) and the resin transfer model(RTM) etc. Within the last 10 years, the synthes…     

Synthesis,structure, and properties of aromatic polysulfides

Polycondensation of haloaromatics and sodium sulfide has been studied. An increase in reactivity of functional groups, a change of the composition of the elementary polymeric unit with a change of the relative amounts of the monomers, and a key role of side-reactions, i.e. intra(molecular) and macrocyclisation, have been revealed. Low-melting isomeric poly(phenylene sulfides), as well as their derivatives, reactive telechelic oligomers, have been prepared. New methods of preparation of poly(arene sulfides) by transarylation of diphenyl sulfide, polymerisation of cyclic aromatic sulfides, or by direct polycondensation of arenes with sulfur under the action of AlCl₃, as well as by polycondensation of aniline with sulfur in the absence of catalysts have been suggested. Structures and properties of newly prepared polymers have been studied.     

Mechanism of Disulfide–Disulfide Interchange in Polysulfide Polymer Melt Blend by Electron Ionization Mass Spectrometry. II

Abstract

The degree of randomization, q, of structural units in melt blends of the polysulfide homopolymers A(PS1) and B(PS2), wherein the disulfide equivalents D _A/D _B = 1, were studied by electron ionization mass spectrometry. Over the temperature range of 207–219°C, the relaxation process, due to the dominant disulfide–disulfide interchange reactions, is postulated to follow an associative reaction mechanism. These intermolecular disulfide–disulfide interactions promote a transient enhancement of the sulfur rank in the activated complex resulting in formation of the randomized co‐polymer AB. The mass spectrometric experimental design enabled measurement of concentrations of reactants A(PS1) and B(PS2), as well as the randomized copolymer AB, by monitoring the abundance of dimer units a₂, b₂, and ab, respectively as a function of time. The degree of randomization, q, was observed in the absence of catalysts or solvents, notwithstanding the solvent/solute and solute/solvent characteristics of the polymer melt blend. The mechanism of this randomization process, was rationalized on the basis of the properties of sulfur, aided by the observation of macrocyclic monomeric and dimeric units during the retro‐polymerization reactions under the EI/MS conditions employed. The model polysulfide polymers A(PS1) and B(P52), used in this study were synthesized from bis(2‐chloroethyl)ether and bis(2‐chloro ethoxy)methane, respectively.     

Sulfur containing polymers.: Aromatic polydithiocarbonates and polythiocarbonates: synthesis and thermal properties

New polydithiocarbonates and polythiocarbonates were obtained by interfacial polymerization of bis(4-mercaptophenyl)methane, bis(4-mercaptophenyl)ether and bis(4-mercaptophenyl)sulfide with phosgene, bisphenol A bischloroformate and bisphenol A polycarbonate oligomers (-OH/-O-CO-Cl terminated). Polymerization process was carried out under interfacial conditions using a phase-transfer catalyst, as earlier described for the synthesis of polydithiocarbonates and polythiocarbonates from 2,2-bis(4-mercaptophenyl)propane. The structures of the polymers were examined by IR and NMR spectroscopies; their thermal properties were investigated by thermogravimetric analysis and differential scanning calorimetry. In particular, the effect of the substitution of one or both the ethereal oxygen atoms of the carbonate group by sulfur has been analyzed by comparing the T_g values and the ability to crystallize of the sulfur containing polymers with those of the corresponding polycarbonates.     

Synthesis of macrocyclic aliphatic disulfide oligomers from dithiols by oxidative coupling with oxygen using a copper‐amine catalyst

A new effective method is provided for the synthesis of macrocyclic aliphatic disulfide oligomers by catalytic oxidation of aliphatic dithiols with oxygen in the presence of a copper‐amine catalyst. Copyright © 2004 John Wiley & Sons, Ltd.     

Copolymerization of elemental sulfur with cyclic(arylene disulfide) oligomers

Copolymerization reactions between cyclic(arylene disulfide) oligomers were studied. The cyclic disulfide oligomers derived from 4,4′-isopropylidene bisbenzenethiol gave soluble polysulfanes via copolymerization with S₈. The copolymerization reactions were studied both in solution and melt by GPC and NMR. Solution copolymerization reactions can only form polysulfanes with up to three to four sulfur linkages; however, melt copolymerization reactions gave polysulfanes with up to seven sulfur linkages (average). The melt copolymerization reactions between cyclic disulfide oligomers derived from 4,4′-thiobis(benzenethiol) and S₈ were studied using DSC, TGA, and DMTA. With increasing contents of sulfur in the polysulfanes, T_gs, 5% weight losses by TGA, and tan δ decreased. With seven sulfur linkages in the polymer, it is a rubber with a T_g of 12°C, a 5% weight loss by TGA of 249°C, and tan δ of 44°C, respectively. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2961–2968, 1997     

Sulfur-containing polymers by the reaction of diphenyl sulfide with sulfur chlorides

The electrophilic reaction of sulfur dichloride with diphenyl sulfide proceeds efficiently at room temperature to yield oligo(phenylene sulfide) in the presence of a catalytic amount of Fe powder. Sulfur dichloride shows higher reactivity than sulfur monochloride. The reaction is promoted through the activation of sulfur dichloride by Fe powder. The polymeric product contains a linear structure linked by disulfide and sulfide bonds.     

Synthesis of poly(thio-1,4-phenylene) by oxidative coupling reaction of diphenyl disulfide with potassium persulfate in strongly acidic solutions

The synthesis of poly(thio- 1,4-phenylene) (PPS) at room temperature by the reaction of diphenyl disulfide with potassium persulfate (K₂S₂O₈) in non-basic solvents, in the presence of trifluoromethanesulfonic acid, is reported. The reaction in chlorinated solvents, such as dichloromethane and tetrachloroethane, resulted in partial oxidation of sulfide to sulfoxide and sulfone. On the other hand, the polymerization proceeded well in nitrobenzene and the PPS formed was free of branches, crosslinks and thianthrene units. The molecular weight of the polymers formed in different solvents were in the range 2000–8000. The reaction proceeded under identical conditions with bis(2,6-dimethylphenyl) disulfide as well, but the polymer yield was lower.     

Automated Solid-Phase Oligo(disulfide) Synthesis

A method for automated solid-phase synthesis of oligo(disulfide)s was developed. It is based on a synthetic cycle comprising removal of a protecting group from a resin-bound thiol followed by treatment with monomers containing a thiosulfonate as an activated precursor. For ease of purification and characterization, the disulfide oligomers were synthesized as extensions of oligonucleotides on an automated oligonucleotide synthesizer. Six different dithiol monomer building blocks were synthesized. Sequence-defined oligomers of up to seven disulfide units were synthesized and purified. The sequence of the oligomer was confirmed by tandem MS/MS analysis. One of the monomers contains a coumarin cargo that can be released by a thiol-mediated release mechanism. When the monomer was incorporated into an oligo(disulfide) and subjected to reducing conditions, the cargo was released under near-physiological conditions, which underlines the potential use of these molecules in drug delivery systems.     

High-Energy Phosphonium Compounds and Their Application to Polymer Synthesis

High-energy phosphonium compounds, the N-phosphonium salts of pyridines, were prepared by the oxidation of phosphorous acid and its esters with mercuric salts or halogens in pyridines, or by a hydrolysis-dehydration reaction of diphenyl and triaryl phosphites or phosphonites. These salts are very reactive to nucleophiles, activating carboxyl, amino, or hydroxyl compounds via the corresponding N-phosphonium salts to yield carboxylic amides and esters in high yields on further aminolysis, alcoholysis, and acidolysis. These reactions, especially the hydrolysis-dehydration reactions with phosphites, were successfully extended to the direct polycondensation reaction of dicarboxylic acids with diamines, of free α-amino acids or dipeptides, and of carbon dioxide and disulfide with diamines under mild conditions, yielding linear polymers of high molecular weight (polyamides, polypeptides, polyureas, and polythioureas).     

Synthesis and conformational studies of amide-linked cyclic homooligomers of a thymidine-based nucleoside amino acid

Cyclic homooligomers of a thymidine-based nucleoside amino acid were synthesized from the linear dimer using BOP reagent in the presence of DIPEA under dilute conditions. Conformational analysis by NMR and constrained MD studies revealed that all the cyclic products had symmetrical structures. The NH and CO groups in these molecules point in opposite directions with near perpendicular orientation with respect to the plane of the macrocyclic ring having CO on the same side as the base.     

The preparation and characterization of novel cocylic(arylene disulfide) oligomers

A series of homo‐ and cocyclic(arylene disulfide) oligomers were synthesized under high dilution conditions by the catalytic oxidation of arylenedithiols with oxygen in the presence of a copper‐amine catalyst in DMAc. The aryl groups contained moieties such as sulfone, ether, and ketone. The free radical ring‐opening polymerization of these cyclic(arylene disulfide) oligomers led to the formation of linear poly(thio arylene)s. The homo‐ and cocyclic(arylene disulfide) oligomers were characterized by gradient high pressure liquid chromatography (HPLC), get permeation chromatography (GPC), ¹H‐NMR, and differential scanning calorimetry (DSC) methods. These cocyclic(arylene disulfide) oligomers except those containing sulfone moiety had lower melt flow temperature as low as 140 °C and therefore could readily undergo free radical ring‐opening polymerization under mild conditions. The glass transition temperatures of these cocyclics ranged from 72.3 to 190.0 °C, while the glass transition temperatures of the polydisulfides derived from these cocyclics ranged from 78.4 to 194.5 °C. In this article, a new method of preparing arylene dithiols 4,4′‐oxybis(benzenethiol) and diphenylmethane‐4,4′‐dithiol is reported. Copyright © 2003 John Wiley & Sons, Ltd.     

Disulfide Click Reaction for Stapling of S-terminal Peptides

A disulfide click strategy is disclosed for stapling to enhance the metabolic stability and cellular permeability of therapeutic peptides. A 17-membered library of stapling reagents with adjustable lengths and angles was established for rapid double/triple click reactions, bridging S-terminal peptides from 3 to 18 amino acid residues to provide 18- to 48-membered macrocyclic peptides under biocompatible conditions. The constrained peptides exhibited enhanced anti-HCT-116 activity with a locked α-helical conformation (IC₅₀=6.81 μM vs. biological incompetence for acyclic linear peptides), which could be unstapled for rehabilitation of the native peptides under the assistance of tris(2-carboxyethyl)phosphine (TCEP). This protocol assembles linear peptides into cyclic peptides controllably to retain the diverse three-dimensional conformations, enabling their cellular uptake followed by release of the disulfides for peptide delivery.     

Polymer-supported syntheses of cyclic oligodepsipeptides

A simple PS cyclization-cleavage method is described for the small-scale synthesis of cyclic oligodepsipeptides with 15 to 27 ring atoms per repeat unit. In selected cases, the cyclic monomers were isolated and characterized. If the cyclic oligomers are needed for the preparation of static or dynamic combinatorial libraries of macrocycles or for entropically-driven ring-opening polymerizations, all members of the family of macrocyclic oligomers are of interest as they all react through equilibration to give the same products.     

Synthesis of poly(arylene disulfide)-vermiculite nanocomposites via in situ ring-opening reaction of cyclic oligomers

An exfoliated poly(4,4^′-oxybis(benzene)disulfide) (POBDS)/vermiculite (VMT) nanocomposite was prepared by using cyclo(4,4^′-oxybis(benzene)disulfide) (COBDS) oligomers and cetyltrimethyl ammonium bromide exchanged VMT. The POBDS/VMT nanocomposites were fabricated in two steps. First, the COBDS oligomers were used to swell and exfoliate organo VMT to afford COBDS-VMT nanocomposite precursor. Subsequently, the exfoliated POBDS-VMT nanocomposite can be made via in situ and instant melt ring-opening polymerization of the COBDS-VMT nanocomposite precursor. High molecular weight POBDS polymer can be formed in a few minutes. The nano scale dispersion of VMT layers within POBDS polymer was confirmed by both the X-ray diffraction patterns and TEM examinations. This methodology provides a potential approach to synthesize high performance polymer nanocomposite.     

Sulfur-substituted tetrahedranes

The stable sulfur-substituted tetrahedrane derivatives 2-4 were synthesized by the reaction of tris(trimethylsilyl)tetrahedranyllithium 1 with diphenyl disulfide, bis(4-nitrophenyl) disulfide, and bis(2,4-dinitrophenyl) disulfide, respectively, and characterized by both NMR spectroscopy and X-ray crystallography. Phenylsulfonyltetrahedrane 5 was prepared by the reaction of 2 and m-chloroperbenzoic acid. The UV-vis absorption spectra of 2-4 suggested an interaction of the σ orbital of the tetrahedrane core and the lone-pair electrons on the sulfur atom, whereas no interaction for 5 was found. Thermal reactions of 2 and 5 are also reported; 2 underwent fragmentation into two acetylene molecules, whereas 5 gave the corresponding cyclobutadiene.     

Degradation of organic sulfur compounds by a coal-solubilizing Fungus

Paecilomyces sp. TLi, a coal-solubilizing fungus, was shown to degrade organic sulfur-containing coal substructure compounds. Di-benzothiophene was degraded via a sulfur-oxidizing pathway to 2,2′-dihydroxybiphenyl. No further metabolism of that compound was observed. Ethyl phenyl sulfide and diphenyl sulfide were degraded to the corresponding sulfones. A variety of products were formed from dibenzyl sulfide, presumably via free radical intermediates. Diphenyl disulfide and dibenzyl disulfide were cleaved to the corresponding thiols and other single-ring products. It was concluded that degradation of organic sulfur compounds byPaecilomyces involves an oxidative attack localized at the sulfur atom.     

Melt polycondensation approach for reduction degradable helical polyester based on l‐cystine

Melt polycondensation approach is developed for new classes of reduction responsive disulfide containing functional polyesters based on l ‐cystine amino acid resources under solvent free process. l ‐Cystine was converted into multi‐functional ester‐urethane monomer and subjected to thermoselective transesterification at 120 °C with commercial diols in the presence of Ti(OBu)₄ to produce polyesters with urethane side chains. The polymers were produced in moderate to high molecular weights and the polymers were found to be thermally stable up to 250 °C. The β‐sheet hydrogen bonding interaction among the side chain urethane unit facilitated the self‐assembly of the polyester into amyloid‐like fibrils. The deprotection of urethane unit into amine functionality modified the polymers into water soluble cationic polyester spherical nanoparticles. The reduction degradation of disulfide bond was studied using DTT as a reducing agent and the high molecular weight polymers chains were found be chopped into low molecular weight oligomers. The cytotoxicity of cationic disulfide nanoparticle was studied in MCF‐7 cells and they were found to be biocompatible and non‐toxic to cells upto 50 μg/mL. The custom designed reduction degradable and highly biocompatible disulfide polyesters from l ‐cystine are useful for futuristic biomedical applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2864–2875