Low Temperature Flexibility Research Articles

Thermoplastic urethane chemical crosslinking effects

AbstractThis paper reviews the chemical structures and attendant polymer morphology that have been advanced to explain the virtual crosslink (VC) phenomenon in segmented polyurethane elastomers. The different chemical methods employed to produce useful vulcanizates from the classical polyurethane elastomer use‐forms (castable liquid, millable gum) through covalent crosslinks (CC) are discussed. And finally, the nature of the polymer property changes occurring when a CC network is superposed on the VC network of a representative thermoplastic poly(ester‐urethane) elastomer composition through the use of a free radical curing agent (organic peroxide) is described. The CC‐VC network polymer of the subject polyurethane composition proved to have greater resistance to: solvation and its effects, stress relaxation, heat distortion, and compression set, and showed much higher modulus values than the VC network polymer. But the CC‐VC network polyurethane also showed less extensibility, tear strength, low temperature flexibility, and flex life. The degrees of these changes are discussed and molecular explanations proposed in some cases.

Poly(fluoroalkoxyphosphazenes)—versatile seal materials

Poly(fluoroalkoxyphosphazene) fluoroelastomers are members of a new family of polymers based on a phosphorous–nitrogen backbone. Physical property evaluation tests have demonstrated that these fluorelastomers possess excellent stress–strain properties, low-temperature flexibility, thermal stability, and resistance to a variety of demanding environments including synthetic lubricants, hydrocarbon fuels, and aqueous caustics. Their service temperature range is about −60° −200°C. Poly(fluoroalkoxyphosphazene) fluoroelastomers have shown the capability to function in severe dynamic applications; i.e., lip seals (1⅞ in. I.D.) performed for >1000 hr at 5500 rpm in MIL L-7808G lubricant at 115°C. Also, O-ring seals successfully completed a 1000-hr dynamic qualification test over a temperature range of −54°–163°C in a rod seal test apparatus. These elastomers can be used for seals, O-rings, gaskets, diaphragms, hose, and protective coatings.

Solution properties of phosphonitrilic fluoroelastomers

AbstractA series of phosphonitrilic fluoroelastomers which have excellent solvent resistance and low temperature flexibility, and which perform well under a broad range of service conditions, have been developed. The solution properties of one of these polymers were studied more extensively in order to develop suitable quality control procedures and to gain a better understanding of the polymer structure. Solvents for these procedures were established, fractionation procedures were developed, and intrinsic viscosity, osmotic pressure, and light‐scattering measurements were conducted. We found this polymer to have a very broad molecular weight distribution. And, although fractionation by molecular weight was effected, the fractions retained a broad molecular weight distribution. Our data do not indicate significant branching for this polymer. As a result of our studies, we have theorized that a supermolecular structure may be present in this polymer.

Cold Crack - Low Temperature Flexibility

A discussion of the factors which affect cold crack and low temperature flexibility - This article is concerned mainly with canvas products as defined by CPAI and will include coated fabrics used for tarpaulins but may, in some cases, overlap into other coated fabric areas. There will be discussion on testing methods for cold crack and index of stiffness as determined by means of a cantilever beam. The effect on cold crack by the major thermoplastics, plasticizer content, fillers, pigments, and processing will be discussed. All these factors have a bearing on cold crack and flex ibility at low temperatures.

Poly(perfluoroether) oxadiazole elastomer system cured with terephthalonitrile oxide

The terpolymerization of N,N′-terephthalonitrile oxide (TPNO), 1,3,5-tricyanobenzene, and oligomeric perfluoroalkylene dinitriles derived from the oligomerization of tetrafluoroethylene oxide yields poly(perfluoroether)-1,2,4-oxadiazole polymers which are soluble in Freon TF and bear pendent nitrile groups as curing sites. The polymerization is a two-step, ambient-temperature reaction. Several different perfluoroether dinitriles are shown to polymerize using this procedure. The syntheses and certain structure/property relationships of the polymers are discussed. Increasing the chain length of the perfluoroalkylene oxide dinitriles results in polymers which range from paraffin-like solids through tough elastomers and, finally, to tacky gums. Tough, crepe elastomer gum with a Tg of −64°C may be obtained in yields of 60–70%. The poly(perfluoroether) oxadiazoles may be milled with additional TPNO and press cured at 95°C (200°F). The following physical properties of the cured polymers are given: compression set, tensile strength, per cent elongation at break, set at break, and Shore A hardness. Thermal stability, moisture stability, and low-temperature flexibility data are also presented for the cured elastomeric polymer.

The preparation and properties of BAB block copolymers based on polyethylene sulphide and polyisoprene

Block copolymers of ethylene sulphide (B) and isoprene (A) have been prepared by anionic synthesis using alkali metal complexes of naphthalene as initiator. Two series of block copolymers have been synthesized, one (based on sodium naphthalenide as initiator) having high molecular weights and the other (based on lithium naphthalenide) having low molecular weights. Physical properties of the block copolymers as a function of composition, molecular weight and polyisoprene microstructure have been studied. Polymers containing high molecular weight polyethylene sulphide sequences were difficult to process without degradation. By lowering the molecular weight of the polyethylene sulphide segment, block copolymers of improved processibility were obtained. The centre block polyisoprene microstructure has been varied from 100% 1,2/3,4 configuration to 80% 1,4 configuration by preparing a “seed” polymer in tetrahydrofuran followed by solvent removal and replacement by hexane. Changes in microstructure affect low temperature flexibility, resilience and tensile strength of the block copolymer. The BAB block copolymers are biphasic and exhibit elastomeric properties with improved network stability compared with polystyrene-polybutadiene-polystyrene ABA block copolymers.

Structure and properties of polypentenamer

AbstractTrans‐1,5‐polypentenamer (TPP) has some similarity to natural rubber partly because of properties that relate to crystallinity and to the position of the crystalline melting point. This similarity makes TPP a unique rubber among other synthetic hydrocarbon polymers. Requirements for attaining a good balance of physical properties include adjustment of both micro and macrostructure with processability. Natta, Dall'Asta, Haas and Pampus have described the preparation of polypentenamers based on tungsten or molybdenum catalysts. Since Eleuterio made his disclosure, there have been many important contributions disclosing special conditions for preparing TPP or variations in catalyst preparation including many catalyst activators. Natta and Dall'Asta vulcanized both the TPP and the amorphous cis‐1,5‐polypentenamer (CPP). They showed that TPP (melting point 23°C) gives good tensile properties even in pure gum vulcanizates characteristic of rubbers that crystallize on stretching. CPP gave better low‐temperature characteristics than other hydrocarbon elastomers (SBR rubber, propylene oxide/allyl glycidyl ether copolymer, cis‐1,4‐polybutadiene). For example, the CPP vulcanizates were less brittle down to −90°C measured by 100 per cent moduli and, in a comparison of temperatures at which retraction occurred, CPP showed a superiority. With CPP from 25°C to −70°C, both tensile strengths and moduli increased without appreciable variation of elongation at break. Since the crystalline melting point at rest is near 20°C for TPP, the elastic behavior is governed by this transition rather than the glass transition point (−90°C).The rate of crystallization for TPP is more rapid compared to natural rubber. Although vulcanization is a factor on elastic behavior, we suggest that further compromise may be necessary to balance the desirable properties related to crystallinity while maintaining elasticity at lower temperatures. The summary of the Haas paper noted that TPP rubber is outstanding except that the abrasion, wet skid and heat build‐up are inferior to existing tread rubber types. Our efforts suggest that TPP is not inferior.In our examination of TPP's having varied or lowered melting points, vulcanizates (tread recipes) with good low temperature flexibility were developed from TPP with Tm of 5°C. Since tack and green strength are dependent on both the micro and macrostructure, properties lost by decreasing the trans content or the Tm were offset by increasing the molecular weight. With higher molecular‐weight TPP, other properties such as heat build‐up and abrasion were improved or made equivalent to other tire rubbers. Thus, by optimizing molecular weight, oil level and processability with the microstructure, a good balance of properties may be produced for TPP rubber.

Thermoplastic Urethane Chemical Crosslinking Effects

This paper reviews the chemical structures and attendant polymer morphology that have been advanced to explain the virtual crosslink (VC) phenomenon in segmented polyurethane elastomers. The different chemical methods employed to produce useful vulcanizates from the classical polyurethane elastomer use-forms (castable liquid, millable gum) through covalent crosslinks (CC) are discussed. And finally, the nature of the polymer property changes occurring when a CC network is superposed on the VC network of a representative thermoplastic poly(ester-urethane) elastomer composition through the use of a free radical curing agent (organic peroxide) is described. The CC-VC network polymer of the subject polyurethane composition proved to have greater resistance to: solvation and its effects, stress relaxation, heat distortion, and compression set, and showed much higher modulus values than the VC network polymer. But the CC-VC network polyurethane also showed less extensibility, tear strength, low temperature flexibility, and flex life. The degrees of these changes are discussed and molecular explanations proposed in some cases.

Study on Dihydric Alcohol containing Ether Linkage. III.

Triesters containing a ether linkage were synthesized and their utilization as plasticizer was examined.Some monoesters were obtained from 1-chloro-3- (2-hydroxyethoxy) -propanol-2 and potassium hexanoate, octanoate, decanoate, laurate, myristate, palmitate or stearate and then they were acylated with acetyl, benzoyl or n-hexanoyl chloride to yield triesters, including diacetates, dibenzoates and dihexanoates, respectively.The triesters were evaluated on the plasticizing effect, through comparison of the effects on the properties of polyvinyl chloride (PVC), with those of dioctyl phthalate (DOP). PVC containing diacetates were considerably inferior than the control (containing only DOP) only in heat stability. With dibenzoates, heat stability was appreciably improved, however, low temperature flexibility lowered. On the other hand, PVC containing dihexanoates showed almost the same degree of heat stability as the control did and were superior than the control in low temperature flexibility. The number of carbon atoms contained in the fatty acid molecules used did not appreciably influence the plasticizing effect.

Phosphonitrilic Fluoroelastomers—A New Class of Solvent Resistant Polymers with Exceptional Flexibility at Low Temperature

Abstract Many commercial elastomers exhibit good solvent resistance and high temperature stability but have limited use at low temperature. Fluorosilicone, which exhibits good low temperature properties, is limited in many dynamic applications by its poor physical strength. Phosphonitrilic fluoroelastomers are being developed for applications which require solvent resistance, low temperature flexibility, and good physical strength over a broad range of service conditions. A brief description of the synthesis and characterization of these new polymers has been presented in the forms of chemical, chromatographical, spectroscopical, physical testing, and rheological studies. The main object of this paper has been to provide an introduction to the art of processing, vulcanization, and reinforcement of these elastomers to produce useful commercial items. These fluoroelastomers can be processed on conventional equipment for dry-mixing rubber. Vulcanization can be effected with either organic peroxides or sulfur-accelerator cure systems. These vulcanizates can be reinforced with silicas, carbon blacks, or silane-treated clays to give stocks with a wide range of modulus, strength, hardness, and service temperatures (−80 to 400° F) in many service fluids and atmospheres. The exceptional solvent resistance, low temperature flexibility, and wide temperature service range indicate that phosphonitrilic fluoroelastomers should find use in items such as O-rings, Arctic fuel hose, lip seals, gaskets, and vibration damping services.

Synthesis and Polymerization Studies of Cyano Epoxides

Abstract The polar epoxides β-cyanoethyl glycidyl ether, cyanomethyl glycidyl ether, β-chloro-β-cyanoethyl glycidyl ether, and 3,4-epoxy valeronitrile were prepared, characterized, and their polymerization reactions studied. Novel cyanoethyla-tion of glycidol produced the β-cyanoethyl glycidyl ether in a quantitative yield. Reported is the first practicable synthesis of epicyanohydrin, which failed to polymerize. Homo-, co-, and terpolymerizations of the polar β-epoxy nitriles with various alkylene oxides were achieved by employing a complex catalyst obtained from an aluminum alkyl, acetyl acetone, and water. The polymers produced a series of vulcanizable elastomers which displayed an ex-cellent balance of solvent resistance and low temperature flexibility, as well as good ozone resistance. The presence of a third monomer such as allyl glycidyl ether was required to facilitate rubber vulcanization. However, it was possible to vulcanize homo- and copolymers of β-chloro-βyanoethyl glycidyl ether through the pendant chlorine atom. Catalyst efficiency in all cases was poor due to the complexing of the aluminum catalyst by the nitrile function.

For excellent hydrolytic stability and low temperature flexibility in urethane coated fabrics...

RETURN TO ISSUEPREVAdvertisementfor excellent hydrolytic stability and low temperature flexibility in urethane coated fabrics...Cite this: Chem. Eng. News 1972, 50, 16, obcPublication Date (Print):April 17, 1972Publication History Published online7 November 2010Published inissue 17 April 1972https://doi.org/10.1021/cen-v050n016.obcCopyright © 1972 AMERICAN CHEMICAL SOCIETYArticle Views61Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (290 KB) SUBJECTS:Stability Get e-Alerts

Antioxidant effects in PVC plasticized with DIDA

AbstractAntioxidants such as bisphenol A (BPA) have long been recommended for retention of physical properties on oven‐aging of PVC plasticized with certain plasticizers. We have shown how BPA inhibits oxidative fragmentation of plasticizers such as diisodecyl adipate (DIDA) and thus decreases apparent volatility, and how it improves retention of modulus, elongation, and low temperature flexibility. Low concentrations are more beneficial than either zero or high concentrations, especially on longer aging. At higher concentrations, although the plasticizer is retained in the PVC, it becomes less efficient at low temperature, and low‐temperature flex is impaired while elongation is preserved. DIDA exudes during oven‐aging unless oxidation occurs to prevent it. When BPA is present, exudation is worst at the most efficient concentrations of antioxidant. This appears to be the normal incompatibility of DIDA at 105°C which is permitted by the antioxidant. On oxidation, the dielectric constant of DIDA rises into the 4–8 range, signifying compatibility with PVC, and the DIDA does not exude.

Tailoring Polymers for Entry into the Atmospheres of Mars and Venus

Abstract Exploring the other planets of our solar system with atmospheric probes and landers places new requirements on polymeric systems. Because of a preoccupation with weight, designers of capsule components are switching over to plastics with increasing frequency. Ablative heat shields, aeroshell structures, antennas, insulators, electronics packaging, parachutes, and many specialty items could be made from plastics which are tailored to the specific environmental needs. In spite of generally poor practices which limit the reproducibility of commercial products, much is being done to delineate the problems set forth by these environments. This paper outlines the specific environments expected for Mars and Venus capsules and discusses some of the efforts in process, or prospective, within or for the National Aeronautics and Space Administration (NASA), to provide the understanding necessary to tailor new composites for these specific environments. Although much of the work is oriented toward ablative heat shield development, the application is generally similar for all of the other capsule components. Based on this work, an idealized polymer would be a reproducible high-temperature plastic with low volatile content, low-temperature flexibility, and a low number of reactive sites after cure. Though we are some distance from this ideal, progress is being made toward this objective.

Now rubber has low-temperature flexibility ...because of Arizona

Now rubber has low-temperature flexibility ...because of Arizona

Now rubber has low-temperature flexibility ...because of Arizona

Now rubber has low-temperature flexibility ...because of Arizona

Triazine Elastomers

Abstract Three technically feasible routes have now been established for preparation of linear perfluoroalkylene triazine polymers. The most advanced route is based on addition polymerization of long chain fluorocarbon dinitriles and diamidines, followed by acylation and cyclodehydration to triazine polymer. Large research samples have been made, but crosslinking to thermally stable vulcanizates is still a problem. An alternate method, active halogen elimination from a difunctional fluorotriazine monomer, has been, demonstrated. High molecular weight polymer has been formed, but it is not elastomeric at room temperature. The low temperature flexibility is a function of structure and not of the method of polymerization, therefore other monomers with longer fluoroalkyl groups hold promise of elastomeric products. The route has attractive economics, but elastomeric products with crosslinking capability must be demonstrated. Coupling of diiodofluoroalkyl triazine monomers employing ultraviolet radiation has been demonstrated. This route is not being pursued because of research required and the predicted high cost of monomer preparation, when compared to the previous two routes. Evaluations of compounded vulcanized triazine elastomer show excellent resistance to hydrocarbon fuels and hydraulic fluids at 370° C and to long term air aging at 300° C. Tensile strength is in the 500 psi range, but is expected to improve with closer control of molecular weight and branching of the polymer. Excellent prospects are in view for fuel tank sealants, wire insulation and elastomer components for hydraulic systems useful in the 300° to 400° C range.

High Quality Foams from NIR Latex

Abstract Foam rubber properties have been measured for NIR latexes as a function of acrylonitrile content of the copolymer and as a function of ratio of NIR latex to NR latex and high modulus SBR latex. Foam rubber made from NIR latex had good aging and oil resistance, combined with the desirable high tensile strength and elongation characteristic of natural rubber foam. Resilience and low temperature flexibility of NIR foams were found to be lower than that achieved with foams of either SBR or NR latexes. Although compression modulus of NIR foam was lower than that of a high modulus SBR foam and approximately equivalent to that of NR foam, it was effectively increased by the addition of either such SBR latex or a high-styrene resin latex.

Now rubber has new, low-temperature flexibility ...because of Arizona

Now rubber has new, low-temperature flexibility ...because of Arizona

Zinc(II) and Cobalt(II) Phosphinate Polymers with Low-Temperature Flexibility

Abstract : In developing the scope of tetrahedral metal phosphinate polymers, a variety of groups were introduced on the phosphorus. While many of the phosphinates reported in the past are tractable, those that can be fabricated are brittle, glasslike solids at room temperature. However, zinc(II) and cobalt(II) phosphinate polymers containing long alkyl sidechains appear to have very low glass transition temperatures. These are the first double-bridged polymers prepared with good low-temperature properties. In order to stabilize the amorphous form of these polymers it is necessary to introduce disorder into their structures. This has been accomplished by making polymers containing two kinds of bridging groups - a class of copolymers which are termed hybrid polymers. The low-temperature properties of some of these double-bridged materials compare favorably with those of the better single-bridged polymers. (Author)