Nylon 6. Chemistry and mechanisms

Reimschuessel, H. K.

doi:10.1002/pol.1977.230120102

Cited by 197 publications

(173 citation statements)

References 142 publications

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“…When the reaction mixture is amorphous (for example, in the melt at high temperatures, or before the phase solidification for the anionic polymerization) because all reactions involved are reversible, a re-equilibration of different species present begins to start to bring the cyclic oligomer composition with the value of the thermodynamically controlled mixture. This corresponds to the results of the last column in Table I (hydrolytic polymerization at 250°C 26 ).…”

Section: Cyclic Dimersupporting

confidence: 82%

“…26 The content of each cyclic oligomer in this study is 3 to 10 times smaller than that of the other studies. However, this is by no means due to any incompleteness of extraction in our cyclic oligomers analysis.…”

Section: Discussioncontrasting

confidence: 64%

“…Each ratio of the by-produced cyclic oligomers in the polymer synthesized with 0.1 mo!% catalyst and 0.1 mo!% chain initiator in this study is close to those in the polymer synthesized by the anionic polymerization by Biagini et al 21 Each ratio of the by-produced cyclic oligomers in the polymer synthesized without chain initiator in this study is close to those in the polymer synthesized by the hydrolytic polymerization. 26 The ratio of each cyclic oligomer in the polymer synthesized with 0.03 mo!% of the chain initiator is intermediate between those with 0.1 mol % of the chain initiator and without the chain initiator. …”

Section: Discussionmentioning

confidence: 98%

“…23 · 25 · 26 Cyclic oligomers in nylon 6 synthesized by hydrolytic polymerization are mainly formed by back-biting of the amino terminal group, in which an amino end-group attacks the internal amide group to form cyclic oligomers. 26 The contents of cyclic oligomers in nylon 6 below 220°C were studied experimentally and theoretically by Andrews et al at l86°C 27 (nylon 6 is in solid state below 220°C). Those at 150°C (the case in this study) have so far never been reported and possibly may be less than above 220°C and at l86°C.…”

Section: Cyclic Dimermentioning

confidence: 99%

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Synthesis of High Molecular Weight Nylon 6 by Anionic Polymerization of ε-Caprolactam. Formation of Cyclic Oligomers

Ueda

Hosoda

Matsuda

et al. 1998

Polym J

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ABSTRACT:The formation of cyclic oligomers in the process of the anionic polymerization of E-caprolactam was studied. Cyclic oligomer contents increased with chain initiator concentration and decrease in catalyst concentration. Cyclic dimer content was much higher than that of cyclic trimer to cyclic hexamer and sensitively influenced by the concentrations of catalyst and chain initiator in comparison with cyclic trimer to cyclic hexamer. A mechanism is proposed in which cyclic dimer is peculiarly formed at the acyl-lactam terminal group.KEY WORDS Cyclic Oligomer/ Cyclic Dimer/ Nylon 6/ Anionic Polymerization/ E-Caprolactam/ Catalyst/ Chain Initiator / The anionic polymerization of e-caprolactam has been extensively investigated because of the high yield and rate of polymerization. 1 -4 Fundamental features such as various catalysts, 2 • 5 • 6 propagation mechanism, 7 -10 and kinetics 11 -16 are well known.The authors carried out systematic studies directed on high molecular weight nylon 6 and obtained stable high-molecular weight polymer (the weight average molecular weight, Mw=9.5 x 10 5 ) by controlling the water content in monomer and the concentration of the catalyst and chain initiator. 1 7 -19 The kinetic equations of their anionic polymerization are in agreement with the ideal rate equation. 20 The formation of cyclic oligomers in anionic polymerization of e-caprolactam has not been studied in detail. Cyclic oligomer content (up to heptamer) has been measured only in a few studies. 21 -23 The proposed mechanism of cyclic oligomer formation still seems insufficient. 24 This study deals with kinetic data of the cyclic oligomer formation in the polymerization as a function of the concentrations of catalyst and chain initiator. The mechanism of the formation is discussed. EXPERIMENT AL MaterialsIndustrial fiber grade e-caprolactam as monomer, ethyl magnesium bromide (EtMgBr; Aldrich Chemical Co., Inc.) as catalyst in 1.0 mo11-1 tetrahydrofuran solution and N-acetyl-e-caprolactam (Ac-CL; Tokyo Chemical Industry Co., Ltd.) as monofunctional chain initiator were used for polymerization. PolymerizationWater in e-caprolactam was removed to less than 0.013 mol¾ by bubbling dry argon gas for 5 h in a three-neck flask at 120°C. Water content was controlled by adding water to this e-caprolactam and measured by a Karl Fischer auto titration equipment (Hiranuma industrial Co., AQV-5S). The chain initiator was injected into ecaprolactam with controlled water content. The mixture of monomer and initiator was poured into a glass 186 tube (inside diameter 20 mm, volume 20 ml) dried beforehand by heating above l00°C under 10Pa vacuum. The catalyst (EtMgBr) solution was injected into the tube via a syringe, and the tube was sealed after unnecessary solvent was evaporated at 10 Pa. The polymerization was carried out with shaking in an oil bath at 150°C (thermostated at± l .0°C).Polymerization was stopped by quenching to dry ice/methanol temperature ( -73°C). The product was shaved with a boring machine and analyzed. Analy...

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Section: Cyclic Dimersupporting

confidence: 82%

Section: Discussioncontrasting

confidence: 64%

Section: Discussionmentioning

confidence: 98%

Section: Cyclic Dimermentioning

confidence: 99%

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Synthesis of High Molecular Weight Nylon 6 by Anionic Polymerization of ε-Caprolactam. Formation of Cyclic Oligomers

Ueda

Hosoda

Matsuda

et al. 1998

Polym J

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“…A discussion of the synthesis, properties, manufacturing, processing, and applications of nylons can be found in books and review articles. [8][9][10][11] …”

Section: Introductionmentioning

confidence: 99%

Hydrogen bonding, mobility, and structural transitions in aliphatic polyamides

Murthy

2006

J Polym Sci B Polym Phys

222

197

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Some salient results in nylon research are reviewed to identify the fundamental principles that are applicable to other strongly interacting or hydrogenbonded polymers, including proteins. The effects of hydrogen bonds on stress-, heat-, and solvent-induced changes in macroscopic properties are discussed. These data provide a window into the chain mobility and linkages between the crystalline and amorphous domains, both of which are important for any predictive model. The changes in the characteristics of the amorphous phase with the crystallinity and orientation require that it be modeled with at least two components: a rigid/immobile/ anisotropic component and a soft/ mobile/isotropic component. The deformation and shrinkage behavior of these polymers are discussed in terms of the relative contributions of the amorphous and crystalline domains and of the interactions between them. The premelting crystalline transition is accompanied by the merging of intersheet and intrasheet diffraction peaks in some nylons, as observed by Brill, and not in others even though the underlying mechanism that gives rise to these transitions, the onset of volume-increasing librational motion of the crystalline stems, is the same. Because the effects of the temperature, deformation, and solvent have a common origin associated with mobility, a fictive temperature can be associated with a given solvent activity or stress level. The magnitude of this fictive temperature is the amount by which the glass or Brill transition temperature is reduced in the presence of solvents ($50 8C) or stress or by which the annealing temperature can be reduced in the presence of a solvent (or active stress) to achieve the same structural state as that of a dry (or static) polymer.

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Thermal decomposition of aliphatic nylons

Levchik¹,

Weil²,

Lewin³

1999

Polym. Int.

372

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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Nylon 6. Chemistry and mechanisms

Cited by 197 publications

References 142 publications

Synthesis of High Molecular Weight Nylon 6 by Anionic Polymerization of ε-Caprolactam. Formation of Cyclic Oligomers

Synthesis of High Molecular Weight Nylon 6 by Anionic Polymerization of ε-Caprolactam. Formation of Cyclic Oligomers

Hydrogen bonding, mobility, and structural transitions in aliphatic polyamides

Thermal decomposition of aliphatic nylons

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