A direct observation of the crosslinking unit in thermally degraded polyamides

Yoshizawa, Yasuo; Saitô, Hazime; Nukada, Kenkichi

doi:10.1002/pol.1972.110100213

Cited by 17 publications

(14 citation statements)

References 8 publications

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“…In addition, the

P A 66 - N H_{2}

runs showed the strong reduction of primary amines, whereas the amount of secondary amine groups doubled, being that 20% of the initial

P A 66 - N H_{2}

sample was recovered as an insoluble gel. These results motivated many researchers to interpret that the nitrogen of secondary amines (first step in Reaction (11–13) in Table ) act as the main branching point. Actually, Garbow et al demonstrated by 13 C NMR that the di‐substituted nitrogen of BHMT reacts rapidly to form tertiary amides (a branching structure) over the polymerization course (Reaction 12).Analogously, the same group performed other polymerization runs between 280 and 290 °C, as: (i) adding 5‐oxononane‐1,9‐dicarboxylic acid to PA 66, (ii) adding carboxyl groups in excess into a model compound, and finally, (iii) polymerizing PA 66 samples containing carboxyl at both ends (samples

P A 66 - C O O H

) .…”

Section: Assumptions and Modelingmentioning

confidence: 90%

“…These results motivated many researchers to interpret that the nitrogen of secondary amines (first step in Reaction (11–13) in Table ) act as the main branching point. Actually, Garbow et al demonstrated by 13 C NMR that the di‐substituted nitrogen of BHMT reacts rapidly to form tertiary amides (a branching structure) over the polymerization course (Reaction 12).Analogously, the same group performed other polymerization runs between 280 and 290 °C, as: (i) adding 5‐oxononane‐1,9‐dicarboxylic acid to PA 66, (ii) adding carboxyl groups in excess into a model compound, and finally, (iii) polymerizing PA 66 samples containing carboxyl at both ends (samples

P A 66 - C O O H

) . This procedure did not cause gelling in 3.5 h in the first case, gelled only after 35 h in the second case and did not form gel in the last one.…”

Section: Assumptions and Modelingmentioning

confidence: 90%

“…This conclusion is also supported by the fact that Reaction (12) was the only one observed in PA 6, which in turn shows a much smaller tendency to form gel than PA 66 . Despite that, tertiary amides ( N , N ‐disubstituted amides, final product of Reaction12 and 13) have been detected for PA 66 as well as tertiary amines . Although tertiary amines can be generated for short residence times (≈3 h) in this medium (Reaction 11), they have been detected only under conditions of excess of amine groups.…”

Section: Assumptions and Modelingmentioning

confidence: 99%

“…Despite that, tertiary amides ( N , N ‐disubstituted amides, final product of Reaction12 and 13) have been detected for PA 66 as well as tertiary amines . Although tertiary amines can be generated for short residence times (≈3 h) in this medium (Reaction 11), they have been detected only under conditions of excess of amine groups. Hence, they are most likely formed in MSP temperature span and not in the SSP.…”

Section: Assumptions and Modelingmentioning

confidence: 99%

“…Especially, PA 66 and PA 126 tend faster to gelation than other aliphatic nylons, such as PA 6, PA 610, and PA 612, which also contain adipic acid subunits . Three main ramification mechanisms have been suggested to explain the source of branches (Table ): (i) aliphatic amines condensation; (ii) Schiff bases (imines) formation; and (iii) isocyanates formation.Different authors performed polymerization runs in the range of 280–290 °C, by: (i) adding bis‐hexamethylene triamine (BHMT) to PA 66, (ii) adding amine groups in excess into a model compound, and finally, (iii) polymerizing PA 66 samples containing one amine end group per chain (samples

P A 66 - N H_{2}

), which in turn had been previously obtained by aminolysis of PA 66 with decylamine . Gel formation occurred in very short times as 3.5, 4, and 1 h, respectively.…”

Section: Assumptions and Modelingmentioning

confidence: 99%

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Modeling of Polyamide 66 Solid State Polymerization: Drawing a Chemical Reaction Scheme

Filgueiras

Vouyiouka

Konstantakopoulou

et al. 2014

Macro Reaction Engineering

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A chemical reaction scheme is proposed here to describe the polyamide 66 (PA 66) solid state polymerization (SSP) with effective kinetic parameters. The main objective of the suggested model is to predict the maximum molecular weight attainable at each SSP isotherm, which is in turn determined by the occurrence of polymer chain degradation coupled to other important side reactions. Accordingly, a number of side reactions have been firstly considered, based on which a comprehensive particle model was constructed to predict PA 66 kinetics, equilibrium, and transport phenomena. The SSP model parameters were estimated with a maximum-likelihood estimator, using data measured under kineticand diffusion-controlled process conditions for reaction temperatures in the range of 160-200 8C and reaction times up to 8 h. Calibration models were also developed to allow the determination of PA 66 solution viscosities.

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“…In addition, the

P A 66 - N H_{2}

runs showed the strong reduction of primary amines, whereas the amount of secondary amine groups doubled, being that 20% of the initial

P A 66 - N H_{2}

P A 66 - C O O H

) .…”

Section: Assumptions and Modelingmentioning

confidence: 90%

P A 66 - C O O H

) . This procedure did not cause gelling in 3.5 h in the first case, gelled only after 35 h in the second case and did not form gel in the last one.…”

Section: Assumptions and Modelingmentioning

confidence: 90%

Section: Assumptions and Modelingmentioning

confidence: 99%

Section: Assumptions and Modelingmentioning

confidence: 99%

P A 66 - N H_{2}

), which in turn had been previously obtained by aminolysis of PA 66 with decylamine . Gel formation occurred in very short times as 3.5, 4, and 1 h, respectively.…”

Section: Assumptions and Modelingmentioning

confidence: 99%

See 3 more Smart Citations

Modeling of Polyamide 66 Solid State Polymerization: Drawing a Chemical Reaction Scheme

Filgueiras

Vouyiouka

Konstantakopoulou

et al. 2014

Macro Reaction Engineering

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Thermal decomposition of aliphatic nylons

Levchik¹,

Weil²,

Lewin³

1999

Polym. Int.

365

254

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An overview of the literature together with selected authors' data on thermal and thermo‐oxidative decomposition of commercial aliphatic nylons (nylon 6, nylon 7, nylon 11, nylon 12, nylon 6.6, nylon 6.10, nylon 6.12) is presented. Despite the high level of research activity and the large number of publications in the field, there is no generally accepted mechanism for the thermal decomposition of aliphatic nylons. Polylactams (nylon 6, nylon 11 and nylon 12) tend to re‐equilibrate to monomeric or oligomeric cyclic products. Diacid–diamine type nylons (nylon 6.6, nylon 6.10 and nylon 6.12) produce mostly linear or cyclic oligomeric fragments and monomeric units. Because of the tendency of adipic acid to fragment with elimination of CO and H2O and to undergo cyclization, significant amounts of secondary products from nylon 6.6 are reported in some papers. Many authors have shown that the primary polyamide chain scission occurs either at the peptide C(O)NH or at adjacent bonds, most probably at the alkyl–amide NHCH2 bond which is relatively the weakest in the aliphatic chain. Hydrolysis, homolytic scission, intramolecular CH transfer and cis‐elimination (a particular case of CH transfer) are all suggested as possible primary chain‐scission mechanisms. There are no convincing results reported which tend to generally support one of these mechanisms relative to the others; rather, it seems that the contribution of each mechanism depends on experimental conditions. This conclusion is also supported by the wide spread of kinetic parameters measured under the different experimental conditions. More uniform results are observed in the literature regarding the mechanism of thermo‐oxidative decomposition of aliphatic nylons. Most authors agree that oxygen first attacks the N‐vicinal methylene group, which is followed by the scission of alkyl–amide NC or vicinal CC bond. Alternatively, it is suggested that any methylene group which is β‐positioned to the amide group methylene can be initially oxidized. There are few mechanisms in the literature which explain discoloration (yellowing) of nylons. UV/visible active chromophores are attributed either to pyrrole type structures, to conjugated acylamides or to conjugated azomethines. Some secondary reactions occurring during the thermal or thermo‐oxidative decomposition lead to crosslinking of nylons. Nylon 6.6 crosslinks relatively easily, especially in the presence of air, whereas nylon 11 and nylon 12 crosslink very little. Strong mineral acids, strong bases, and some oxides or salts of transition metals catalyse the thermal decomposition of nylons, but minimize crosslinking. In contrast, many fire retardant additives promote secondary reactions, crosslinking and charring of aliphatic nylons. © 1999 Society of Chemical Industry

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