Formation of phenolic resins: mechanism and time dependence of the reaction of phenol and hexamethylenetetramine as studied by carbon-13 nuclear magnetic resonance and fourier transform infrared spectroscopy

Sojka, Stanley A.; Wolfe, Roger A.; Guenther, Gary D.

doi:10.1021/ma50006a076

Cited by 61 publications

(37 citation statements)

References 1 publication

(1 reference statement)

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“…First, basic characterization of both types of PFRB resins by 13 C CP/MAS NMR and 11 B MAS NMR techniques was performed; the resulting spectra are depicted in Figure 1. All of the peaks in the 13 C CP/MAS NMR and 11 B MAS NMR spectra were assigned according to literature data [11][12][13][14][15]29,30 and subsequently verified by DFT calculations (Table 1).…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Structure and Distribution of Cross-Links in Boron-Modified Phenol–Formaldehyde Resins Designed for Soft Magnetic Composites: A Multiple-Quantum ¹¹B–¹¹B MAS NMR Correlation Spectroscopy Study

et al. 2015

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Despite the extensive use of boron-modified phenol−formaldehyde polymers as insulating materials in soft magnetic composites (SMCs), the structure and arrangement of the inorganic cross-linking units in these systems have not been fully elucidated. To clarify the structure, configuration, and distribution of the boron cross-links in these materials, phenol−formaldehyde resins modified by boric acid were synthesized and characterized using advanced multiplequantum 11 B− 11 B MAS NMR correlation techniques combined with the quantum chemical geometry optimizations and the subsequent 11 B NMR chemical shielding calculations. The analyses of the resulting spectra revealed a well-evolved (highdensity) phenol−formaldehyde polymer network additionally strengthened by nitrogen and boron cross-links. The boron-based cross-links were attributed to monoester (ca. 10%) and diester (ca. 90%) complexes (six-membered spirocyclic borate anions) with strictly tetrahedral coordination (B IV ). During the thermal treatment, the monoester and diester borate complexes underwent additional transformation in which the spirocyclic borate anions were more tightly incorporated into the polymer matrix via additional N-type (amino) cross-links. A 11 B− 11 B double-quantum correlation MAS NMR experiment revealed that the majority of the monoester and diester borate complexes (ca. 80%) were uniformly distributed within and effectively isolated by the polymer matrix, with an average 11 B··· 11 B interatomic distance greater than 6 Å. A non-negligible part of the spirocyclic borate anion complexes (ca. 20%), however, existed in pairs or small clusters in which the average 11 B··· 11 B interatomic distance was less than 5.5 Å. In addition, the formation of homodimers (diester−diester) was demonstrated to be preferred over the formation of heteroclusters (monoester−diester).

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Section: ■ Experimental Sectionmentioning

confidence: 99%

Structure and Distribution of Cross-Links in Boron-Modified Phenol–Formaldehyde Resins Designed for Soft Magnetic Composites: A Multiple-Quantum ¹¹B–¹¹B MAS NMR Correlation Spectroscopy Study

et al. 2015

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“…The reaction mechanism and kinetics of the solventless synthesis were proposed by Liu and Ishida in order to use this procedure to prepare a large quantity of benzoxazine monomers 5) . Benzoxazines, as stable side products, in low yield can be formed by decomposition of hexamethylenetetramine at higher temperature in the solid state in the presence of phenol 6) . Bishop et al mentioned in their paper that only 2-phenylaminomethylphenol can be obtained by condensation of phenol with 1,3,5-triphenylhexahydro-1,3,5-triazine 3) .…”

Section: 35-triphenylhexahydro-135-triazine -Active Intermediatementioning

confidence: 99%

1,3,5-Triphenylhexahydro-1,3,5-triazine - active intermediate and precursor in the novel synthesis of benzoxazine monomers and oligomers

Brunovska¹,

Liu²,

Ishida³

1999

Macromol. Chem. Phys.

142

108

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SUMMARY:The benzoxazine monomer synthesis via 1,3,5-trialkyl(aryl)hexahydro-1,3,5-triazine intermediate is followed by 1 H NMR, FT-IR, and SEC. A model compound, 1,3,5-triphenylhexahydro-1,3,5-triazine, is synthesized independently and its reaction with bisphenol-A and paraformaldehyde in stoichiometric amounts is also followed by 1 H NMR. Additional model compounds, 1,3,5-trimethyl(ethyl)hexahydro-1,3,5-triazine, are used instead of a primary amine to synthesize bifunctional benzoxazine monomers, bis(3,4-dihydro-2H-3-methyl(ethyl)-1,3-benzoxazinyl)isopropane, via novel solventless reaction with bisphenol-A in the presence of paraformaldehyde. The mechanism of this reaction is proposed.

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“…The preparation of phenolic resins based on phenol and hexamethylenetetramine (hexamine) has been studied in some detail (Megson 1958;Sojka et al 1981). These resins go through a stage in which tribenzyl-, dibenzyl-and monobenzylamines are the majority of the cross-linking bridges between phenolic nuclei.…”

Section: Introductionmentioning

confidence: 99%

Hardening Mechanisms by Hexamethylenetetramine of Fast-Reacting Phenolic Wood Adhesives - A CP-MAS ₁₃C NMR Study

Pizzi¹,

Tékély²

1996

HFSG

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Phenols of high reactivity with formaldehyde and phenolic resins derived from them, such as resorcinol and resorcinol-formaldehyde (RF) resins, have been shown by I3 C NMR to react with hexamethylenetetramine (hexamine) with the formation of both benzylamine and methylene bridges to form hardened resins. In the final hardened network the proportion of benzylamine bridges appears to be considerably higher than that of methylene bridges directly connecting two phenolic nuclei. The benzylamine bridges appear to have high stability and after cooling the resin at ambient temperature after hardening at 100°C remain stable, without rearrangement to methylene bridges. Heating the hardened networks at 110°C for periods of up to 30 minutes cause some rearrangement of benzylamine to methylene bridges for networks formed by direct hardening of resorcinol by hexamine. This does not appear to occur, or occurs to a minimal extent for preformed resorcinol-formaldehyde (RF) resins hardened with hexamine, with significant consequences as regards the application and the formaldehyde emission of hexaminehardened wood adhesives systems.

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Formation of phenolic resins: mechanism and time dependence of the reaction of phenol and hexamethylenetetramine as studied by carbon-13 nuclear magnetic resonance and fourier transform infrared spectroscopy

Cited by 61 publications

References 1 publication

Structure and Distribution of Cross-Links in Boron-Modified Phenol–Formaldehyde Resins Designed for Soft Magnetic Composites: A Multiple-Quantum ¹¹B–¹¹B MAS NMR Correlation Spectroscopy Study

Structure and Distribution of Cross-Links in Boron-Modified Phenol–Formaldehyde Resins Designed for Soft Magnetic Composites: A Multiple-Quantum ¹¹B–¹¹B MAS NMR Correlation Spectroscopy Study

1,3,5-Triphenylhexahydro-1,3,5-triazine - active intermediate and precursor in the novel synthesis of benzoxazine monomers and oligomers

Hardening Mechanisms by Hexamethylenetetramine of Fast-Reacting Phenolic Wood Adhesives - A CP-MAS ₁₃C NMR Study

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Formation of phenolic resins: mechanism and time dependence of the reaction of phenol and hexamethylenetetramine as studied by carbon-13 nuclear magnetic resonance and fourier transform infrared spectroscopy

Cited by 61 publications

References 1 publication

Structure and Distribution of Cross-Links in Boron-Modified Phenol–Formaldehyde Resins Designed for Soft Magnetic Composites: A Multiple-Quantum 11B–11B MAS NMR Correlation Spectroscopy Study

Structure and Distribution of Cross-Links in Boron-Modified Phenol–Formaldehyde Resins Designed for Soft Magnetic Composites: A Multiple-Quantum 11B–11B MAS NMR Correlation Spectroscopy Study

1,3,5-Triphenylhexahydro-1,3,5-triazine - active intermediate and precursor in the novel synthesis of benzoxazine monomers and oligomers

Hardening Mechanisms by Hexamethylenetetramine of Fast-Reacting Phenolic Wood Adhesives - A CP-MAS 13C NMR Study

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Structure and Distribution of Cross-Links in Boron-Modified Phenol–Formaldehyde Resins Designed for Soft Magnetic Composites: A Multiple-Quantum ¹¹B–¹¹B MAS NMR Correlation Spectroscopy Study

Structure and Distribution of Cross-Links in Boron-Modified Phenol–Formaldehyde Resins Designed for Soft Magnetic Composites: A Multiple-Quantum ¹¹B–¹¹B MAS NMR Correlation Spectroscopy Study

Hardening Mechanisms by Hexamethylenetetramine of Fast-Reacting Phenolic Wood Adhesives - A CP-MAS ₁₃C NMR Study