Liquid Polysulfide Polymers Research Articles

Novel Crosslinking System for Poly-Chloroprene Rubber to Enable Recyclability and Introduce Self-Healing.

The introduction of dynamic bonds capable of mediating self-healing in a fully cross-linked polychloroprene network can only occur if the reversible moieties are carried by the cross-linker itself or within the main polymer backbone. Conventional cross-linking is not suitable for such a purpose. In the present work, a method to develop a self-healable and recyclable polychloroprene rubber is presented. Dynamic disulfide bonds are introduced as part of the structure of a crosslinker (liquid polysulfide polymer, Thiokol LP3) coupled to the polymer backbone via thermally initiated thiol-ene reaction. The curing and kinetic parameters were determined by isothermal differential scanning calorimetry and by moving die rheometer analysis; tensile testing was carried to compare the tensile strength of cured compound, healed compounds and recycled compounds, while chemical analysis was conducted by surface X-ray Photoelectron Spectroscopy. Three formulations with increasing concentrations of Thiokol LP-3 were studied (2, 4, 6 phr), reaching a maximum ultimate tensile strength of 22.4 MPa and ultimate tensile strain of 16.2 with 2 phr of Thiokol LP-3, 11.7 MPa and 10.7 strain with 4 phr and 5.6 MPa and 7.3 strain with 6 phr. The best healing efficiencies were obtained after 24 h of healing at 80 °C, increasing with the concentration of Thiokol LP-3, reaching maximum values of 4.5% 4.4% 13.4% with 2 phr, 4 phr and 6 phr, respectively, while the highest recycling efficiency was obtained with 4 phr of Thiokol LP-3, reaching 11.2%.

New liquid polysulfide polymer terminated with silyl group

AbstractThe terminal SH of liquid polysulfide polymer was capped with a silyl group. This polymer was hydrolyzed immediately by moisture at ambient temperature and returned to the original polymer. The compounds of this new polymer and the various curing agents of the conventional polysulfide polymer became moisture curable and of use as one‐component sealants and adhesives. The curing speed of these compounds is very fast compared with that of not only conventional one‐component polysulfide sealants, by more than three times, but also of other one‐component sealants at 20°C under 30% humidity. Their storage stability is good. Their cured products showed physical properties comparable to those of the two‐component polysulfide compounds. In particular, the compound of this polymer and isocyanate prepolymer showed good elasticity and good weatherability. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2642–2649, 2004

Sodium birnessite curing of liquid polysulfide polymers

Sodium birnessite curing of liquid polysulfide polymers

Detection of a new crosslinking and properties of liquid polysulfide polymer

Polysulfide polymer was found in the 19th century. At present, this polymer consists of the repetition of disulfide linkage and diethyl formal and has SH terminals. This liquid polymer (LP) is cured by lead dioxide. We studied polysulfide polymerization and elastomeric mechanical properties of cured LP. The condition of polymerization greatly influenced its elastomeric mechanical properties. These phenomena could not be explained from the point of residual unreacted chlorine or produced OH terminals. We found that additional crosslinking sites are produced during polymerization besides crosslinking agents trichloropropane (TCP) by using the Insensitive Nuclei Enhanced by Polarization Transfer (INEPT) method. We proposed their chemical structures and reaction scheme of their formation. TCP and also these additional crosslinking sites influence the modulus of cured LP. The sum of the intensity of their crosslinking sites by 13C-NMR had good correlation with 300% modulus of cured LP. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 59–66, 1999

The cure chemistry of polysulfides

Liquid polysulfide polymers can be cured by a wide variety of compounds and through a number of reaction paths. The most commonly used system is the oxidation of the thiol terminal groups in the presence of metal peroxides. Addition and substitution reactions are also possible with such diverse products as epoxy resins, isocyanates, acrylics and anhydrides. Although having a notworthy commercial history little is known of the detailed cure mechanism and the article discusses some of the current research being carried out.

New synthesis of liquid polysulfide polymers in the presence of hydrazine. II. The synthesis of linear polymers from 1,1′‐[methylenebis(oxy)]‐bis‐[2‐chloroethane] and Na2S3 or Na2S2.5

Liquid polysulfide polymers with the thiol groups on the end of the chains and of the average molecular weight of 7000–510 g mol−1 have been obtained by the reaction of BClE and Na2S3, i.e., Na2S2.5 in the presence of hydrazine. The average molecular weight of the obtained polymers depends on the quantity of hydrazine used for the syntheses. With the aim to obtain polymers of the similar average molecular weight it is necessary to use on average 0.5 mol of hydrazine per polymer segment less if Na2S2.5 is used instead of Na2S3. The sulfur content in the obtained polymers is on average less than 2 sulfur atoms per polymer segment and amounts to 1.90 sulfur atoms when Na2S3 is used and is 1.76 sulfur atoms per polymer segment when Na2S2.5 is used for the synthesis. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1369–1373, 1997

New synthesis of liquid polysulfide polymers in the presence of hydrazine. II. The synthesis of linear polymers from 1,1?-[methylenebis(oxy)]-bis-[2-chloroethane] and Na2S3 or Na2S2.5

Liquid polysulfide polymers with the thiol groups on the end of the chains and of the average molecular weight of 7000–510 g mol−1 have been obtained by the reaction of BClE and Na2S3, i.e., Na2S2.5 in the presence of hydrazine. The average molecular weight of the obtained polymers depends on the quantity of hydrazine used for the syntheses. With the aim to obtain polymers of the similar average molecular weight it is necessary to use on average 0.5 mol of hydrazine per polymer segment less if Na2S2.5 is used instead of Na2S3. The sulfur content in the obtained polymers is on average less than 2 sulfur atoms per polymer segment and amounts to 1.90 sulfur atoms when Na2S3 is used and is 1.76 sulfur atoms per polymer segment when Na2S2.5 is used for the synthesis. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1369–1373, 1997

New synthesis of liquid polysulfide polymers in the presence of hydrazine. I. Synthesis of linear polysulfide polymers from 1,1?-Methylenebis(oxy)]-bis-[2-chloroethane] and sodium tetrasulfide

The results of our studies show that liquid linear polysulfide polymers of an average molecular weight 4260–1030 g mol−1 can be obtained by the reaction of sodium tetrasulfide and 1,1′-[methylenebis(oxy)]-bis-[2-chloroethane] in the presence of 2.0–5.0 mol of hydrazine and at least 4.0 mol of sodium hydroxide/mol of hydrazine in a one-step procedure. The disulfide polymers in the form of sodium mercaptide are soluble in the supernatant liquid from which they are separated by acidification of the solution to a pH value of about 4. The average molecular weight and the content of sulfur in the obtained linear polymers were determined and their IR spectra were recorded. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1363–1367, 1997

New synthesis of liquid polysulfide polymers in the presence of hydrazine. I. Synthesis of linear polysulfide polymers from 1,1′‐Methylenebis(oxy)]‐bis‐[2‐chloroethane] and sodium tetrasulfide

New synthesis of liquid polysulfide polymers in the presence of hydrazine. I. Synthesis of linear polysulfide polymers from 1,1′‐Methylenebis(oxy)]‐bis‐[2‐chloroethane] and sodium tetrasulfide

EPR–spin-trapping studies of the heterogeneous oxidative curing of some liquid polysulfide polymers: evidence for the mediation of thiyl radicals, disulfide radical-anions and oxygen-centred radicals

The use of spin-trapping techniques (with DMPO and MNP) in conjunction with EPR and NMR spectroscopic studies has allowed mechanistic details to be obtained about the process whereby thiols (particularly liquid polysulfide polymers) can be linked via reaction with inorganic oxidants (especially activated MnO2). The roles of activation, basic additives, and oxygen are interpreted in terms of the involvement of thiyl radicals which can undergo both dimerization and reaction with thiolate anions, evidently to give disulfide radical-anions as important reaction intermediates.

Characterization of cured polysulfide polymers by thermal degradation: Pyrolysis‐GC and thermogravimetric studies

AbstractPolymers prepared by curing thiol‐terminated liquid polysulfide polymer [HS(RS2)nRSH, R = CH2CH2OCH2OCH2CH2] with p‐quinonedioxime, PbO2, and MnO2 were studied by pyrolysis‐GC and thermogravimetry. Characteristic differences were observed in the composition of the pyrolyzates under flash pyrolysis at 420 and 470°C. The concentration of the cyclic monomer, 1,3‐dioxa‐6,7‐dithionane, in the pyrolyzates was found to vary considerably from polymer to polymer. The change in mechanism with the extent of degradation and the corresponding overall activation energies were evaluated by thermogravimetry. The pyrolysis‐GC and thermogravimetric data were shown to provide partial characterization of the substrates. Mn appears to be in a coordinated complex in the MnO2‐cured polymer.

Thermal degradation of liquid polysulfide polymers: Pyrolysis–GC–MS and thermogravimetric studies

AbstractThe thermal decomposition of Thioped, a liquid polysulfide polymer based on dichloroethyl formal, was studied using pyrolysis–GC–MS. The nature and composition of the products of pyrolysis at 358 and 485°C are given. A striking feature of the product analysis is the presence of several disulfide compounds only at the higher decomposition temperature. The pyrolysis‐GC of other liquid polysulfide polymers (LP‐2, LP‐32, LP‐3, and LP‐33) showed that molecular weight had only marginal effect on the product composition. Ionic and radical mechanisms were considered to account for the product formation. Isothermal and dynamic thermogravimetric studies were carried out to differentiate between the two mechanisms. The results were found to be in agreement with a free radical mechanism, with cleavage of the formal CO linkage as the preferred mode of initiation. The overall activation energy for the decomposition was found to be 190 kJ mol−1.

Thiol modification of difunctional castor oil and its utility as room temperature setting elastomeric material

AbstractDifunctional castor oil has been reacted with thioglycolic acid for the synthesis of castor oil dithioglycolate (CODT). Elastomeric products have been obtained from CODT alone and in combination with liquid polysulfide polymer LP‐33 by oxidative cure with manganese dioxide. Semireinforced (SRF) carbon black has been used as a filler. CODT has also been evaluated as a flexibilizer for liquid epoxy resin (Synpol 200).

Chemistry and Technology of Polysulfide Sealants

Abstract The highly reactive terminal mercaptans of liquid polysulfide polymers can be converted into high molecular weight products very easily at ambient temperatures by oxidation or by reaction with other active polymers. Polysulfides have excellent solvent resistance, predictable cure, good low-temperature performance, good weathering, and excellent adhesion to many substrates. This combination of properties has given polysulfide polymers a modest but significant position as specialty polymers since their commercialization in 1929. Polysulfide sealants have found wide acceptance in industries, e.g., construction, aircraft, automotive, marine, and insulating glass. In fact, polysulfide sealants were the first elastomeric sealants used in the construction industry and continue today, to a large extent, the standard against which other sealants are compared. Polysulfide sealants, although facing strong challenges by silicones and polyurethanes, continue to be the dominant segment of the elastomeric sealant market [1–6].

Polysulfide Sealants

Abstract Sealants based on polysulfide liquid polymers are widely used in a number of applications. These sealants are solvent and chemical resistant, having good flexibility and adherence to many substrates such as steel, aluminum, glass, concrete, wood, etc. These are used to line fuel tanks of aircraft and to seal fuel tanks and rivetted joints in aircraft. These sealants, being water resistant, are widely used in ship building to seal decks and planking. Since these sealants have good weather resistance and can withstand stress and strain, they are widely used in the building industry. They are found to be very satisfactory in modern curtain walls and in sealing windshields of motorcars. Their use in airfield and runway constructions is well known. These sealants generally have a two-pot system consisting of (i) a base caulk containing a liquid polysulfide polymer, fillers, plasticizers, adhesive promotors, thickening agents, accelerators or retarders and (ii) a curing agent. Sometimes accelerators and retarders are used as a third pot system to regulate the pot life of caulking compounds.

Preparation of a Liquid Polysulfide Polymer for Leather Impregnation

Preparation of a Liquid Polysulfide Polymer for Leather Impregnation

Low Temperature Expansion of Polysulfide Rubbers

Abstract A novel method for producing a cellular cured rubber product at room temperature has been developed. Pourable liquid polysulfide polymers are treated with a conventional oxidizing curative and selected water-sensitive or oxidation-sensitive blowing agents. Standing at ambient temperature the viscous liquid mixture gradually “rises” and cures to form a finely porous cellular rubber product. Conventional curatives employed include oxidizing agents such as lead peroxide and cumene hydroperoxide. These convert terminal or pendant thiol groups in the polysulfide polymer chains to chain-connecting disulfide linkages. Water is a byproduct of the curing reaction. In the presence of water-sensitive blowing agents such as, (1) metal salts of azodicarboxylic acid or, (2) metal hydride compounds the water produced in the cure reacts to form copious amounts of nitrogen or of hydrogen. Alternatively, oxidation-sensitive blowing agents such as p, p′-oxybis-(benzene sulfonyl hydrazide) react directly with the oxidizing curative to form nitrogen gas. The blowing reactions are concurrent with cure and efficient and controllable expansion can be achieved. The unique process offers possible economies and special properties in applications of liquid polysulfide rubbers as potting compounds, joint sealants, solvent resistant forms, and cold casting compounds.

Chemorheological study of cured polysulfide liquid polymers

AbstractThe effect of curing agents and their reaction products upon the disulfide interchange reaction of cured liquid polysulfide polymers was studied. The curing process involved the oxidation of the mereaptan terminals of the liquid polymer to disulfide linkages or the reaction of these end groups with some polyfunctional reagent. Several different types of cure were attempted on the same batch of the liquid polymer including oxidation by metallic oxides, organic peroxides, and hydroperoxides, p‐quinonedioxime, and catalyzed air oxidation. Cures were also obtained by the use of diisocyanates. The disulfide interchange was studied by means of stress relaxation. It was found that the rate of exchange was greatly accelerated by the presence of ionic or alkaline materials. In their absence the exchange reaction proceeded quite slowly. The incorporation of excess sulfur also increased the reaction rate. The mechanism of the reaction is believed to be predominantly ionic.