The Rates of Reaction of 1-Alkenyl Isocyanates with Methanol

Satô, Masao

doi:10.1021/ja01500a027

Cited by 65 publications

(33 citation statements)

References 4 publications

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“…Even thought the general trend is clear, the values obtained for oxalic acid in this and the following analyses should be treated somewhat cautiously due to the limited number of data points. All three figures indicate that the reactions are apparently initially secondorder, but that at higher conversions large positive deviations are observed, indicating autocatalysis or some other change in the reaction mechanism (18,19). Autocatalysis by the urethane groups in the isocyanate-alcohol reaction is well known (17,18,21), whereas the autocatalytic effect of the amide groups formed by the isocyanatecarboxylic acid reaction has not been reported, to the best of the authors' knowledge.…”

Section: Resultsmentioning

confidence: 80%

“…All three figures indicate that the reactions are apparently initially secondorder, but that at higher conversions large positive deviations are observed, indicating autocatalysis or some other change in the reaction mechanism (18,19). Autocatalysis by the urethane groups in the isocyanate-alcohol reaction is well known (17,18,21), whereas the autocatalytic effect of the amide groups formed by the isocyanatecarboxylic acid reaction has not been reported, to the best of the authors' knowledge. However, a catalytic effect of added amides and ureas in the amine-isocyanate reaction has been observed (21).…”

Section: Resultsmentioning

confidence: 80%

“…The kinetics of polyurethane reactions are usually characterized by second order kinetics (17)(18)(19)(20), as follows:…”

Section: Resultsmentioning

confidence: 99%

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Synthesis of Poly(ether urethane amide) Segmented Elastomers

Penhasi¹,

Aronhime²,

Cohn³

1993

ACS Symposium Series

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A new series of polyurethane block copolymers was synthesized, based on the use of dicarboxylic acids as novel chain extenders. Poly(tetramethylene glycol) of molecular weight 2000 was used as the soft segment, which was reacted in a 1:2 ratio with hexamethylene diisocyanate. Amide groups were formed in the reaction of isocyanate groups with carboxylic groups. The effect of the type of diacid on the kinetics of the polymerization was determined by monitoring both the disappearance of isocyanate groups and the increase in intrinsic viscosity. The type of diacid had a pronounced effect on the kinetics, with the rate of reaction of diacid with isocyanate in the following order: oxalic acid > fumaric acid > sebacic acid. The kinetics of a model system comprising two moles of isocyanate and one mole of diacid were found to follow second order kinetics modified by the addition of an autocatalytic term. The polymer was characterized by elemental analysis, infrared spectroscopy, nuclear magnetic resonance spectroscopy, viscometry and thermal analysis. The time of the reaction was found to be important in determining the structure and properties of the segmented polymer, as observed by thermal analysis and viscometry. In addition, polymers prepared with oxalic and fumaric acids were of lower molecular weight when synthesized in THF as opposed to DMA, probably due to the lower compatibility of the polymers formed in THF.Thermoplastic polyurethane elastomers are one of the most important groups in the class of thermoplastic elastomers (2-5). A typical polyurethane elastomer is a block (or segmented) copolymer of the type (AB) n , which is composed of alternating hard and soft segments which are generally not compatible chemically. This incompatibility leads to phase separation and the creation of micro-domains, in which hard block domains are dispersed in the matrix of the soft segment. The hard segments serve as physical crosslinking sites due to their local order at normal use temperatures and impart strength and prevent flow. On the other hand, the soft segment glass transition temperature (Tg) is normally well below the use temperature, thus imparting flexibility to the system. The combination of physical crosslinks and flexibility allows for the very high elongations typical of these thermoplastic elastomers (d). One additional

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Section: Resultsmentioning

confidence: 80%

Section: Resultsmentioning

confidence: 80%

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Synthesis of Poly(ether urethane amide) Segmented Elastomers

Penhasi¹,

Aronhime²,

Cohn³

1993

ACS Symposium Series

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“…The investigated reactions involved either: (a) the synthesis of polymers in stoichiometric reactions between diisocyanates and low molar mass diols or macrodiols 2,20,23,27,30 ; or (b) the synthesis of oligomers by reaction between macrodiols and diisocyanates in excess. For MDI, Eceiza et al 2 proposed a third-order rate equation based on Sato's expression, 32 that includes the catalytical effects of alcohol and urethane groups. For reactions between PPG and TDI Grepinet et al 18 and Majoros et al 22 adopted second-order kinetics.…”

Section: Introductionmentioning

confidence: 99%

Linear segmented polyurethanes: I. A kinetics study

Polo

Spontón

Jaramillo

et al. 2017

J of Applied Polymer Sci

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This work investigates the two-step polymerization between methylene diphenyl diisocyanate (MDI), two different poly(tetramethylene oxide) macrodiols, and 1,4-butanediol (BD) as chain extender. At the end of the prepolymerization, the reaction mixture contains MDI in excess and a prepolymer with isocyanate end group. Then, BD and a solvent (tetrahydrofuran) were added to start the finishing stage under nominal stoichiometric equilibrium. The reaction was analyzed by Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance ( 1 H-NMR), and size exclusion chromatography. 1 H-NMR was employed to follow global concentrations of unreacted isocyanate end groups and internal urethane groups. This information enabled to estimate the following "effective" rate constants: k 1 5 1.07 3 10 23 L mol 21 s 21 for the prepolymerization; and k 2 5 1.94 3 10 24 L mol 21 s 21 for the finishing stage. These values are subject to errors caused by biases introduced in the recipe, in the measurements, in the reaction conditions, in the quality of reagents, and in the reaction mechanism assumptions. Such errors also explain the dispersion of the published rate constants values. The 1 H-NMR measurements also enabled to estimate the evolution (with extent of reaction) of the numberaverage number of structural units along the prepolymerization and finishing stages; and such estimates reasonably verify Flory's classical expressions.

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“…Reaction speed is also control by a tin complex catalyst concentration and kinetic law must integrate its effect. Sato's model [7] is appropriated to describe this kinetics.…”

Section: Introductionmentioning

confidence: 99%