The use of 13 carbon nuclear magnetic resonance (NMR) spectroscopy in the molecular characterization of macromolecules has advanced our knowledge into structural areas that have been nearly impossible to measure by other spectroscopic techniques. Innovative applications have led to determinations of polymer configurational distributions, comonomer sequence distributions, average sequence lengths, structure and distribution of short chain branches, and analyses of nonreactive end groups. As a result, the importance of 13C NMR to the field of polymer science cannot be overemphasized. The key to the success of 13C-NMR studies in defining polymer molecular structure has been a structural sensitivity which encompasses more than just a few functional groups or carbon atoms. A sensitivity to polymer repeat unit sequences of lengths from two to as many as five, seven, and even nine contiguous repeat units [1,2] has been observed. Of course, any structural technique that senses a unique response from as f...

A review of high resolution liquid 13carbon nuclear magnetic resonance characterizations of ethylene-based polymers

Fast identification of microplastics in complex environmental samples by a thermal degradation method.

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 NHCH2 bond which is relatively the weakest in the aliphatic chain. Hydrolysis, homolytic scission, intramolecular CH transfer and cis-elimination (a particular case of CH 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 NC or vicinal CC 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

Thermal decomposition of aliphatic nylons

Review: the development and applications of thermally assisted hydrolysis and methylation reactions

A pyrolysis-derivatisation-gas chromatography technique for the structural elucidation of some synthetic polymers

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

Structural characterization of polyolefins by pyrolysis—hydrogenation glass capillary gas chromatography☆

Tapered block polymers of styrene and isoprene were prepared by copolymerization of these two monomers, containing a trace amount of THF. s-BuLi was used as an initiator, and benzene as the polymerization solvent. Analyses based on pyrolysis gas chromatography and 1H NMR indicated that a considerable amount of mixing of these two monomers took place in the block polymer chain, e.g., for TB-1 to TB-3. Such mixing in the primary structure is considered phenomenologically to give rise to the polystyrene-rich block chain and polyisoprene-rich block chain. The repulsive interaction between the two block chains is much weaker than that between the pure polystyrene and polyisoprene block chains, and this enhances the mixing of the polystyrene-rich chain and polyisoprene-rich chain, resulting in a microdomain structure consisting of the polystyrene-rich phase and polyisoprene-rich phase. Owing to this segmental mixing within each phase, the tapered polymer exhibits a lower critical temperature and the unique mechanical properties, in compared to ideal block polymers. The tapered block polymers have the unique solubilizing power of the corresponding homopolymers, arising from their microdomain structures.

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Tamio Nagaya

Papers

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

Structural characterization of polyolefins by pyrolysis—hydrogenation glass capillary gas chromatography☆

Structure and Properties of Tapered Block Polymers of Styrene and Isoprene

Microstructural Characterization of Polypropylenes by High-Resolution Pyrolysis-Hydrogenation Glass Capillary Gas Chromatography

Pyrolysis-gas chromatographic studies on head-to-head polystyrene