Review: Auto-oxidation of aliphatic polyamides

The literature on oxidation kinetics of polyamides and model compounds has been reviewed in order to try to extract suitable information for non-empirical kinetic modeling. Polyamide characteristics are systematically compared to polyolefin ones, these latter being more extensively studied. From kinetic analysis point of view, it is shown that oxidation attacks predominantly α amino methylenes of which C–H bond is considerably weaker than the other methylenes. As a result, propagation by H abstraction is considerably faster in polyamides than in polyethylene for instance. Termination by radical combination is also very fast. Another cause of PA oxidizability is the instability of α amino hydroperoxides linked to the inductive effect of nitrogen. This instability is responsible for many key features of oxidation kinetics especially the absence of induction period.     

Cyclizations in hyperbranched aliphatic polyesters and polyamides

Hyperbranched aliphatic polyesters of 2,2′-bis-(hydroxymethyl) propanoic acid and hyperbranched aliphatic polyamides obtained from new carboxy- and amino-functionalized caprolactams were studied by NMR spectroscopy and MALDI-TOF mass spectrometry. Ring-chain equilibria taking place through intramolecular hydroxy-ester, carboxy-amide or amine-amide interchanges and leading to the formation of cyclic branches or end-groups were found to exert a predominant influence on the molar mass of these hyperbranched polymers. A number of intra- or intermolecular side reactions, such as the formation of ethers in polyesters and the formation of anhydrides, imides, amidines and secondary amines in polyamides were also detected and resulted in polymer crosslinking on prolonged heating. The existence of such ring-chain equilibria and side-reactions make the control of hyperbranched polymer structure much more difficult than generally accepted.     

Stereoregular polyamides derived from methylene-L-tartaric acid and aliphatic diamines

Stereoregular polyamides containing two chiral backbone carbons in the repeating unit were prepared by polycondensation of bis(pentachlorophenyl) 2,3-O-methylene-L -tartrate with 1,9 and 1,12-alcanediamines activated as N,N′-bis(trimethylsilyl) derivatives. The polymers were characterized by elemental analysis, IR, and ¹H-NMR spectroscopy, and differential scanning calorimetry. Both viscosimetry and GPC were used to estimate the molecular weights which ranged between 6000 and 44000. These polytartaramides were readily soluble in chloroform, displayed moderate optical activity in solution, and formed highly crystalline films.     

Lower-frequency infrared spectra and structures of some typical aliphatic polyamides

The Polarized lower-frequency infrared spectra (800–33 cm^-1) of nylon 66 (α form), nylon 77 (γ form), and nylon 6 (both α and γ form) have been examined. The spectral changes which occur on complex formation of the polyamides with iodine-potassium iodide solution and on subsequent iodine desorption have been studied in relation to the changes in the polymer structures. On the basis of these results, most of the stronger bands have been reasonably assigned to the vibrations characteristic of the amide group and the methylene chain of the polyamides, and some new structure–frequency correlations have been established for the polymers.     

Synthesis of polyamides from pseudo dibenzoylphthaloyl chlorides and aliphatic diamines

New pseudo dibenzoylphthaloyl chlorides, namely, 2,5-dibenzoylterephthaloyl, 4,6-dibenzoylisophthaloyl, and 4,6-di(p-toluyl)isophthaloyl chlorides, were synthesized as monomers. The ring-opening polyaddition reaction of the pseudo dibenzoylphthaloyl chlorides with aliphatic diamines in N-methyl-2-pyrrolidone afforded a new class of polyamides having inherent viscosities of 0.2 ～ 0.6 in quantitative yield. The solution polymerization was almost completed within 30 min at room temperature. All of the polyamides were soluble in a wide range of solvents including tetrahydrofuran. These polymers began to decompose at around 300°C both in air and under nitrogen as determined by differential thermal analysis (DTA) and thermogravimetric analysis (TGA).     

Hydrogen bonding,mobility, and structural transitions in aliphatic polyamides

Some salient results in nylon research are reviewed to identify the fundamental principles that are applicable to other strongly interacting or hydrogen‐bonded 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 °C) 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. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1763–1782, 2006     

Studies on thermal degradation of aliphatic polyamides by pyrolysis-glass capillary chromatography

A series of aliphatic polyamides samples (five kinds of α-aminocarboxyclic acid-type nylons and seven kinds of diamine-dicarboxyclic acid-type nylons) were pyrolysed in a vertical microfurnace-type pyrolyser at 550°C, and their high-resolution pyrograms were obtained by a glass capillary gas chromatograph directly attached to the pyrolyser. The characteristic peaks on the resulting pyrograms were identified using a mass spectrometer, which was also attached to the gas chromatograph. On the basis of the various characteristic degradation products identified, such as hydrocarbons, mononitriles, lactams, cyclopentanone hydrocarbons containing one amide group and mononitriles containing one amide group, general mechanisms for the degradation of the aliphatic polyamides were formulated.     

Synthesis of aliphatic polyamides in the dispersion medium of oxidized asphalt

The possibility of modifying oxidized asphalt by performing polycondensation of maleic anhydride with aliphatic amines of various chemical structures in the dispersion medium was considered. The influence of the reactant structures and reaction conditions on the physicomechanical and structural-rheological properties of the polymer-modified asphalt was examined.     

Effect of ammonium polyphosphate on combustion and thermal degradation of aliphatic polyamides

Chain fragments with amide and imide groups are the most abundant degradation products of aliphatic polyamides (APA) which derive from scission of the N-alkylamide bond (-CH₂-NH-). In the case of polyamide 6.6 (PA-6.6), also carbodiimide structures and methyl chain ends are formed, which derive from scission of -CH₂-C(=O)- bond. Cyclic compounds can be formed besides chain fragments, depending on the type of APA. Ammonium polyphosphate (APP) reacts with APA on heating forming phosphoric esters which decompose giving products similar to those obtained from pure APA. APP increases the yield of carbodiimides from PA-6.6 which trimerise to triazine structures. The fire retardant mechanism of APP is discussed on the basis of the thermal degradation of the mixtures.     

Dynamic-mechanical properties and melting points of some aliphatic and partially aromatic polyamides

Some aliphatic and partially aromatic polyamides have been prepared from hexamethylene diamine and the following dicarboxylic acids: deca-, octa-, hexa-methylenedicarboxylic, p-carboxymethylphenoxyacetic, p-carboxyethylphenoxyacetic, p-phenylenedipropionic, p-phenylenediacetic, p-carboxymethoxyphenoxyacetic, β(p-carboxymethyl)phenylpropionic.The dynamic-mechanical properties at 110 Hz have been measured between ?140° and about 200. Three relaxation processes α β and γ have been found: only the main transition α appreciably depends on chemical structure.The influences of the length of repeating unit and of in-chain substitution on melting points, crystallinity and the dynamic-mechanical α transition have been investigated. The results have been discussed in terms of chain flexibility, chain packing and intermolecular forces.     

Solubility of additives in polyethylene and aliphatic polyamides. The effect of oxidation

The solubility of diphenylamine, phenyl benzoate and diphenyl methane in high-density polyethylene and various polyamides has been studied as a function of oxidation and of sample annealing.

Oxidative destruction of topological structures forming the non-polar sorption centers and accumulation of new-formed polar groups, participating in sorption of polar compounds, result in complicated dependencies of solubility upon oxidation, in some cases showing minima.     

Synthesis and thermal properties of soluble silicon containing phenylated aromatic–aliphatic polyamides

Journal of Thermal Analysis and Calorimetry - Aromatic polyamides find many applications in diverse and critical areas due to their high thermal stability coupled with high mechanical properties....     

Physico-chemical analysis of semi-crystalline PEEK in aliphatic and aromatic solvents

Polyether ether ketone (PEEK) is a semi-crystalline thermoplastic polymer having excellent mechanical and thermal properties. Exposure of this polymer to aliphatic and aromatic solvents can lead to degradation or swelling of the polymeric material. The present work described the plasticization and stability analysis of semi-crystalline PEEK under different aromatic and aliphatic solvent environment. A variety of solvents (acetone, benzene, benzyl alcohol, chloroform, methanol, and toluene), based on their Hildebrand’s Solubility Parameter, were chosen for investigation. The physico-chemical characteristics of virgin and treated polymeric samples were investigated using Gas Chromatography–Mass Spectrometry (GC–MS), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), and Fourier Transform Infrared Spectroscopy (FTIR) techniques. The results indicated that the solvent exposure did not significantly affect the thermal behavior and chemical structure of the polymer. However, it seems that certain components of the polymer were leached into the solvent phase as revealed by the GC–MS analysis. The present study identified PEEK as a potentially suitable polymer for the applications where high resistance to aliphatic and aromatic solvents is needed.     

Synthesis and characterization of soluble,blue-fluorescent polyamides and polyimides containing substituted p-terphenyl as well as long aliphatic segments in the main chain

A novel class of semiflexible polyamides and polyimides bearing substituted p-terphenyl as well as long aliphatic segments in the main chain were synthesized through pyrylium salts. Characterization of polymers was accomplished by inherent viscosity, elemental analysis, FT-IR, NMR, UV-vis luminescence spectroscopy, X-ray analysis, differential scanning calorimetry, thermomechanical analysis, thermogravimetric analysis, isothermal gravimetric analysis, and water uptake measurements. Polyamides displayed a degree of crystallinity and dissolved in polar aprotic solvents containing lithium chloride, as well as in trichloroacetic acid. Polyimides were amorphous and showed an excellent solubility, being soluble in various common solvents. The solutions of polyamides in DMF were blue-fluorescent with maxima at 362–370 nm. The emission maxima were not influenced appreciably upon the structure of the pendent groups and the length of the aliphatic spacers of backbone. The polymers possessed T_gs at 98–131°C and exhibited a satisfactory thermal stability. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3646–3656, 1999     

Synthesis of polybenzodipyrrolediones by thermal cyclodehydration of polyamides derived from dibenzylidenebenzodifurandiones and aliphatic diamines

A new class of polyheterocycles, polybenzodipyrrolediones (PBP), has been synthesized successfully by the two-step polymerization of dibenzylidenebenzodifurandiones with aliphatic diamines. New bislactone monomers, 3,5-dibenzylidene-3,5-dihydro-1H,7H-benzo[1,2-c:4,5-c′]difuran-1,7-dione and 3,7-dibenzylidene-3,7-dihydro-1H,5H-benzo[1,2-c:4,5-c′]-difuran-1,5-dione, were synthesized from pyromellitic dianhydride and phenylacetic acid. The ring-opening polyaddition reaction of the bislactones with aliphatic diamines in a polar solvent afforded novel polyamides having inherent viscosities of 0.1–1.0 in quantitative yield. The solution polymerization was almost completed within several hours at 80°C, while it required approximately a week to its completion at room temperature. Dimethyl sulfoxide and N-methyl-2-pyrrolidone were preferred solvents for the polymerization. The open-chain polyamides were subsequently cyclodehydrated by heating at 240°C to give PBP having high molecular weight. The aliphatic PBP were soluble in hot polar solvents such as N-methyl-2-pyrrolidone, m-cresol, and nitrobenzene. They began to decompose at about 400°C in a nitrogen atmosphere as determined by thermogravimetric analysis.     

Synthesis and liquid-crystalline properties of thermotropic polyamides containing flexible rodlike units and aliphatic spacers

New polyamides with high molecular weights consisting of flexible rod-like mesogenic units (4,4'-diphenyl and 3,4'-diphenyl moieties having bent linkages in the central parts) and aliphatic spacers were synthesized and the thermotropic liquid-crystalline properties were investigated. Differential scanning calorimetry, texture observations by polarizing microscopy, miscibility tests and X-ray analysis suggested that the polymers showed well-defined thermotropic smectic mesophases. The polyamides containing 4,4'-diphenyl moieties had higher transition temperatures and formed more stable liquid-crystalline phases than the polyamide composed of the 3,4'-diphenyl unit with a kinked bond.     

Synthesis and properties of polyamides from 2,5-furandicarboxylic acid and aromatic and aliphatic diamines

Russian Chemical Bulletin - Polyamides based on the 5-hydroxymethylfurfural derivative (2,5-furandicarboxylic acid dichloroanhydride) and diamines of both aromatic and aliphatic series were...