Thermal stability of urethane

Oxazolidone-Modified Isor anurate Foams. The 2-oxazolidone, or 2-oxazolidinone, linkage is considered to be a cyclic urethane linkage, but its thermal stability is much higher than that of a urethane linkage. Kordomenos et al (207) compared the thermal stabilities of urethane, oxazolidone and isocyanurate linkages in terms of activation energy by using model compounds. The results obtained were as follows. 

The thermal stability of urethane elastomers can be determined by the DMA method. The temperature at which the storage modulus (G ) decreases significantly in the rubbery region is considered to be the limit of thermal stability of the elastomers [16]. From the G values of the elastomers, it was determined that HER extended materials were stable up to 160 °C whereas HQEE extended elastomer showed a 10 °C higher stability. 

Thermal stability of urethane group is relatively low. It was already stated that it depends on the groups to which it is attached, being the highest for aliphatic isocyanate aliphatic alcohol (approx, dissociation temperature 250 °C), then aliphatic alcohol aromatic... 

In order to address these issues, a brief discussion of thermal, oxidative, and hydrolytic stability of urethanes will be offered, so as to aid the adhesion scientist in designing a urethane adhesive with the desired durability. 

There appear to be conflicting reports regarding the degradation of urethanes. For example, some urethanes are reported to have relatively poor hydrolysis resistance and good biodegradability [77], while other urethanes are reported to be so hydrolytically stable that they have been successfully used as an artificial heart [78]. Both reports are correct. It will be shown that the thermal, oxidative, and hydrolytic stability of urethanes can be controlled, to some degree, by the choice of raw materials used to make the urethane. 

Polythiocarbamates, 23 735-738 Polythiocarbonates, 23 626, 725-729 thermal stability of, 23 726-727 Polythioesters, 23 729-732 preparation of, 23 730-731 Polythioether-based urethane sealants, 22 36... 

When hexafluoroacetone reacts with amides, urethanes [25], tliioarnides [26], ami dines [27], sulfonamides [28, 29], sulfinamides [30], and 0,0-dialkyl-amido-phosphates [37], the coirespondmg semiamidals are formed m nearly quantitative yield The thermal stability of these adducts toward the retro reaction increases with the nucleophikcity of the ammo compound [5] Many polyfluonnated carbonyl compounds react likewise [32 33] On treatment of ureas [34], thioureas [34], thioamides [26], and C,N diarylamidines L27, 35] first with hexa- fluoroacetone and then with dehydrating agents, heterodienes are obtained (equation 4)... 

The thermal stability of PU is generally controlled by the thermally weakest link the urethane bond. In the case of PU/PDMS hybrid system, any decrease in the thermal stability might be explained by thermal instabilities in PDMS structure. 

Modification of poly(carbodiimide) foams with polyols afford hybride foams containing urethane sections. However, the thermal stabilities of the poly (urethane carbodiimide) foams are lower. Using isocyanate trimerization catalysts, such as l,3,5-tris(3-dimethylaminopropyl)hexahydro-s-triazine, in combination with the phospholene oxide catalyst gives poly(isocyanurate carbodiimide) foams with improved high temperature properties. The cellular poly(carbodiimide) foams derived from PMDI incorporate six-membered ring structures in their network polymer structure. ... 

Applications for the Stabaxol stabilizers include thermoplastic polyester urethanes, polyesteramide thermoplastic elastomers, castable polyester urethanes, polyester polyols, monofilament PET fibers, polycarbonates, polycarbonate/PETblends, EVA copolymers and poly(caprolactones). The thermal stabilization of poly(ethylene sulfide) is also accomplished with 4 % hexamethylenebis(t-butyl)carbodiimide and 2 % diphenylacetylene. Also, alternating carbon monoxide/ethylene copolymers are stabilized using aromatic carbodiimides. ... 

Careful studies of polyurea formations are generally quite difficult. Low-molecular-weight disubstituted ureas have such low solubility in most solvents that precipitation causes experimental difficulties the problem is even worse with many polyureas. In addition the rather limited thermal stability of polyureas at temperatures of about 200°C has detracted from what otherwise might have been a significant interest in these polymers for fibres. The major commercial interest has not been in pure polyureas, but rather in polymers containing polyurea blocks, as in water-blown polyurethane foams and in polyurea—urethane elastomers. The complexity of these commercial systems, which are nearly always crosslinked, has made kinetic studies difficult. 

Polyfester urethanes) based on HER chain extenders behaved in the same way as poly(ether nrethanes). When the high MW diol content of the extender is increased, the storage modulus is decreased due to the reduction of the hard segment content. As was seen from thermal analysis, the thermal stability of the HER-HP extended elastomer is slightly higher than the technical grade materials. 

It is well known that conventional polyester-based urethane elastomers extended with butanediol can withstand continuous use temperatures of about 80 °C. At higher temperatures, a reduction in the physical and mechanical properties is seen due to degradation of the material. The thermal stability of the polyurethanes is related to the nature of the starting materials such as the aromatic diisocyanate and diol chain extender. The hard segment of the urethane elastomer is primarily responsible for temperature resistance, and the soft segment determines the material s performance at low temperature. 

Wang and co-workers [4] have discussed the thermal stability of PDMS-urethane copolymers using a combination of differential scanning calorimetry, dynamic mechanical analysis and cone calorimetry. 

Poly(ester urethane) and poly(ether sulfone) blends with or without Thermal degradation of blends using TGA The presence of polysulfone caused a rise in thermal stability of the Filip and Vlad 2004... 

Increase in crosslink density, type of crosslinking and introduction of isocyanurate ring structures in the polymer-chain backbone has a strong beneficial effect on the thermal stability of polyurethanes and is discussed later in this chapter. It is known that thermal stability increases with increasing isocyanate content of urethane elastomers, and in addition to the formation of the thermally stable isocyanurate rings, stability is influenced by the different types of urethane-based groups formed, as shown in Table 3.9a. 

Sometimes in polyols small amounts of unsaturation are present which affect the light and thermal stability of the urethane hence detection and estimation of this unsaturation is desirable. Carbon-carbon unsaturated compounds in the sample are reacted with mercuric acetate and methanol in a methanolic solution to produce acetoxy-mercuricmethoxy compounds and acetic acid. The amount of acetic acid released in this equimolar reaction, which is determined by titration with standard alcoholic potassium hydroxide, is a measure of the unsaturation originally present. Because the acid cannot be titrated in the presence of excess mercuric acetate due to the formation of insoluble mercuric oxide, sodium bromide is added to convert the mercuric acetate to the bromide, which does not interfere. 

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