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Mechanism of polyphenolic tannin resin hardening by hexamethylenetetramine: CP–MAS 13 C‐NMR
Author(s) -
Pizzi A.,
Tekely P.
Publication year - 1995
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1995.070561215
Subject(s) - hexamethylenetetramine , benzylamine , tannin , chemistry , phenol , methylene bridge , methylene , proanthocyanidin , condensed tannin , organic chemistry , nucleophile , polyphenol , medicinal chemistry , nuclear chemistry , catalysis , food science , antioxidant
Abstract Polyflavonoid tannins have been shown by 13 C‐NMR to react with hexamethylenetetramine (hexamine) at considerably higher rates than with phenol with the formation of both benzylamine and methylene crosslinks to form hardened resins. Predominantly prodelphinidintype tannins appear to present a much higher proportion of benzylamine bridges than of methylene bridges, while in procyanidin‐type tannins the proportion of the two types of crosslinks appear to be comparable. The greater the nucleophilicity of the flavonoid tannin A‐rings, the greater is the proportion of benzylamine bridges which appear to form. At parity of the type of tannins, the faster the reaction with hexamine, the higher the proportion of benzylamines which appear to form. © 1995 John Wiley & Sons, Inc.