I.Ya. Slonim

13C-NMR determination of the structure on linear-branched urea-formaldehyde resins☆

Abstract A 13 C-NMR method has been developed for the determination of the structure of urea-formaldehyde resins. The signals have been identified on the basis of spectra produced from a number of model compounds, and the dependence of the spectra on the urea formaldehyde components ratio, but also from the duration of the reaction. The signals are those of the methylene and methylate linkages in the linear chain, while they are those of the methoxymethylene groups, the radicals of tetra-, tri-, di- and mono-substituted urea, and of free urea, free methanol, and free formaldehyde (methylene glycol and polyoxymethlyene glycol oligomers) in the branches. Branches will form in the early stages of condensation under industrial scale production conditions when the urea: formaldehyde ratio is from 1 : 2 to 1 : 1·3, and the pH = 4·5−8·5, and the products will have a linear-branched structure.

A 13C-NMR study of equilibria in the urea-formaldehyde system

The composition of equilibrium reaction mixtures formed in reaction of urea with formaldehyde in neutral, aqueous solution, has been determined by 13C-NMR analysis. The equilibrium constants have been calculated for all possible methylolation reactions, involved in formation of asymmetric N,N-dimethylolurea and tetramethylolurea. The equilibrium constants for formation of hemiformal groups on secondary and tertiary urea nitrogen atoms were determined and the correlation was found between these constants and the electron density on the carbon atom of the methylol group, as characterized by the 13CH2 chemical shift. The value of the constant in formation of dimethylene-ether bridges was also determined.

Determination of the structure of cyclochain urea-formaldehyde resins by 13C NMR analysis

A method has been developed for 13C NMR analysis of the structure of urea-formldehyde resins containing imidazolidone, triazinone and uronic rings. It is shown that the reaction of urea and formaldehyde with ammonia or hexamethylene tetramine results in the formation of triazinone rings stabilized by methylol groups linked to the “amine” nitrogen of the ring. In a urea-formaldehyde system uronic ring formation takes place in an acid or alkaline medium with a large excess of formaldehyde in the system. Rings of both types add formaldehyde with formation of methylol groups and methylene and methylene ether bridges. The obtained cyclochain structures complement the linear-branched structures formed by urea residues with methylol groups and bridges between the letter.

The structural changes which occur during the synthesis and setting of urea-formaldehyde resins (UFR)☆

Abstract A quantitative description of the structure of urea-formaldehyde resins by means of the 13 C-NMR spectra has been developed. The structure has been investigated at all stages of synthesis and during the initial stages of setting. The branched structures are shown to form at the start of resin formation. A partial fracture of the dimethylene ester bonds and a formaldehyde liberation takes place in an acid medium. Polymer chain propagation takes place during setting as a result of methylene bridges formation, but the polymers retain the linear structure with branches, although the branching intensity increases.

Kinetics of polysulphone synthesis: nuclear magnetic resonance spectroscopy and rheological investigation

Abstract Time-dependent changes in monomers, dimers, end reactive groups and central links occurring in the synthesis of polysulphone derived from dichlorodiphenylsulphone and the sodium salt of diphenylolpropane in dilute solution in dimethylsulphoxide were investigated by nuclear magnetic resonance spectroscopy. On this basis, a kinetic model of the reaction was designed and elementary reaction constants, which appeared to be dependent on the chain length, were determined. Simultaneously, the time-dependent change in the viscosity of the reaction medium in concentrated solutions was measured and the results obtained were analysed by the rheokinetic method. A correlation was found to exist between the rheokinetic constants and the rate constants in sufficiently high-molecular-weight products determined by nuclear magnetic resonance spectroscopy.

Investigation of isomerism in polyphenylquinoxalines by 13C NMR

Isomerism has been observed in polyphenylquinoxalines by 13C NMR spectroscopy and the properties of the isomers have been measured qualitatively. It has shown that changing the solvent in which polycondensation is carried out enables the ratio between the isomers to be varied within certain limits (from 45 : 55 to 60 : 40).

Differences in the repeated units in polyamido-acids: An investigation by 13C NMR☆

13C NMR spectroscopy has been used to observe and assess quantitatively the differences in monomer units in amido-acids obtained by reaction between the dianhydride of 3,3′,4,4′-dipehnyloxidetetracarboxylic acid and 9,9-bis-(4′-aminophenyl) fluorene (a polyamido-acid) and aniline (a model amido-acid). It has been shown that the opening of the anhydride ring occurs in such a way that the carbonyl carbon atom of the ring, located in the meta position relative to the ether oxygen bridge, preferentially undergoes nucleophilic attack and the anhydride rings of the dianhydride used may be considered to be independent. It has been established that the solvent in which the reaction is carried out has a marked effect on the selectivity of the process.

Radiation polymerization of tetrafluoroethylene adsorbed of some highly porous substrates

Abstract By means of a number of physicochemical methods (plotting of adsorption isotherms, NMR and infrared spectroscopy) a study has been made of some properties of tetrafluoroethylene (TFE) adsorbed on porous substrates of different types, as well as of specific features of polymerization brought about in the adsorbed layer. It is shown that the strength of the bond between TFE and the surface of the adsorbents studied increases in the order silica gel IREA-zeolite NaY-zeolite CaA. Infrared spectra of TFE in varioys states of aggregation, including in the absorbed state (on silica gel), were obtained. It was found that there is correlation between the strength of the bond between the absorbed monomer molecules and the surface, and the temperature region in which effective polymerization occurs in the adsorbed layer. The adsorbents studied have a substantial sensitizing effect on post-polymerization of TFE. It is shown that the rate of radiation polymerization of TFE on silica gel is controlled by the concentration of monomer in the adsorbed layer and not in the gas phase, the order of reaction with respect to monomer being unusually high. An explanation of these effects is given.

13C NMR study of the structure of polyethylene-polyamines

The signals in the 13C NMR spectrum of a commercial sample of polyethylene-polyamine have been assigned and an additive scheme for calculating the chemical shifts proposed. The content in the technical product of all possible 18 structural fragments (linear and cyclic) has been determined from the spectrum. The number of primary, secondary and tertiary nitrogen atoms in the polyethylene-polyamine molecule has been calculated and the number average M determined.

1H and 13C NMR analysis of the synthesis of polyarylene sulphonoxides based on diphenylolpropane and dichlorodiphenylsulphone

the method of 1H and 13C NMR analysis has been used to investigate reaction mixtures formed in the synthesis of oligoarylene sulphonoxides from the sodium salt of diphenylolpropane and dichlorodiphenylsulphone. A quantitative study was carried out to determine the amount of different endgroups and of monomeric and “dimeric” products formed at some stages in the synthesis. Number-average molecular weights were determined for oligoarylene sulphonoxides in the reaction mixture.