The thermal oxidation of polyamide 6 and 6,6 gives rise to azomethine groups (Schiff's bases) as a result of the reaction of aldehyde and ketocarbonyl groups with amino end groups. During the course of degradation, these azomethine groups react with each other in an aldol-type condensation to produce conjugated unsaturated oligoenimine structures that absorb in the UV/VIS range. During aldol condensation, the amino end groups are re-formed, allowing them to react again with the carbonyl groups which are continuously supplied by thermal oxidation (auto-oxidation) to form azomethine groups once more. The concentration and sequence length distribution of the oligoenimine structures can be correlated to the concentration profiles of the amino end groups, carboxyl end groups, and carbonyl groups, in a kinetic model. The concentrations of the individual oligo-enimine species calculated with the aid of the model, are in agreement with the figures found experimentally with UV spectroscopy. Sterically hindered phenols inhibit the formation of carbonyl groups, and thus indirectly counteract the formation of oligoenimine structures (kinetic model for the autoxidation of polymers).

In heat-treated polyamide 6 and polyamide 6.6 fibres UV/VIS-active chromophores are found, which originate from two different sources: one type of chromophore (structured UV spectrum) arises during polycondensation and the spinning of the fibres (molten phase), the other (nonstructured UV spectrum) occurs as a result of a thermo-oxidation of the solid fibre. The chromophore which forms during solid-phase thermo-oxidation is based on conjugated oligoenimines . . .+ A = &A j =N-. . . , as is shown by a combination of UVNIS spectroscopy and fluorescence excitation and emission spectroscopy with chemical analysis. The concentration of the various oligoenimine species depends upon the temperature and duration of the thermooxidation. For a temperature of 160°C and a duration of 2 hours, for example, the following oligoenimine concentrations were found (UV spectroscopy with computer-aided evaluation): for i = 0 44; i = 1: 13; i = 2 4; i = 3: 1; i = 4 0,3 (values expressed in mmol/kg).

Studies with benzyl alcohol and other substances (acetophenone, dimethylacetamide, dimethylsulfoxide) interacting with poly( m -phenylene isophthalamide) fibers have shown that the carrier effect in the dyeing process takes place through a balanced combination of several factors. For a substance acting as a carrier, the distribution equilibrium must be on the side of the fiber. This is the case if the substance has only a limited hydrophilicity, indicated by a low solubility of the carrier in the dyeing liquor. In order to be effective, it is not sufficient that the sorption of the carrier takes place only in the interior of the fiber; it must also take place on the fiber surface. If the carrier layer on the fiber surface is removed, the dye uptake rate decreases. An optimal carrier effect is accompanied by an increase in the degree of crystallinity and changes in the mechanical properties (decreased tensile strength and elongation at break, as well as increased Young's modulus). When combined with the carrier substance, water is also able to enhance the dye uptake rate (co-carrier). Electrolytes do not influence the sorption of carrier.During the last decades, many reviews (Piedmont Section [20], E16d [2], and Hendrix [6J) and original works have been published (especially Ingamells et al. [3-5, 8-12] and Herlinger et al. [7]) on the effect of dyeing accelerants, which are usually called carriers.Ingamells et al. explained the carrier effect by the free volume theory: Dye diffusion depends on the segmental mobility of the polymer chains, which in turn depends on the glass transition temperature T~, being an essential characteristic of viscoelastic behavior. Carriers decrease the glass transition temperature and therefore act as plasticizing agents. A dyeing transition temperature Td occurs under dyeing conditions. Dye uptake depends on the plasticization state of the fiber and rises sharply at T~.There is a relationship between Td and T. [9,10].The distribution of the carrier between the liquor and the fiber plays a decisive role in reducing of T, and is dependent on the structure of the carrier. Equimolar sorptions cause equal effects regardless of the nature of the carrier [41, but there is no correlation between fiber swelling and the carrier effect. Actually, substances that cause only a small amount of swelling are the best plasticizing agents [4].Although equivalent concentrations of carrier (in the fiber) influence the dye diffusion rate to the same extent, the equilibrium dye uptake depends on the structure of the carrier. This fact has been attributed to a specific interaction between the different carriers and dyestuffs in the fiber interior [11,12].In some studies on dyeing polyacrylonitrile fibers with basic dyes, Ingamells et al. used the carrier benzyl alcohol, which is important for poly(m-phenylene isophthalamide) fibers [5]. Herlinger et al. [7] confirmed Ingamells' results on the carrier effect in a system of poly(ethylene terephthalate) fibers/disperse dyes. They also broadened these results w...

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SYNOPSISOne of the main obstacles to the wider application of chitin in polymeric materials is its poor tractability due to unfavorable solubility properties. The solubility can be enhanced by introducing bulky acyl residues into the polymer (as in butyrylchitin and valeroylchitin). However, if modification is carried out with shorter-chain carboxylic acids (as in acetylchitin), the solubility remains poor. By substituting the acetyl residues partially by butyryl residues (mixed ester formation), exclusive use of the bulky carboxylic acids can be avoided and yet good solubility is achieved. These relationships were shown by using high molecular weight mixed chitin esters, prepared with methanesulfonic acid as the solvent and catalyst. The mixed chitin esters, varying both in the overall degree of substitution (1.5-1.9) and the molar ratios of butyryl-to-acetyl residues (1 : 0.62 to 1 : 0.72), were characterized by IR spectroscopy, DSC, elemental analysis, and 'H-NMR spectroscopy (in trifluoromethanesulfonic acid); the latter allowed the degree of substitution to be determined as well as the molar ratio of butyryl-to-acetyl residues. 0