Gelation and cross-link inhomogeneity of phenolic resins studied by small- and wide-angle X-ray scattering and 1H-pulse NMR spectroscopy

摘要: Abstract The gelation mechanism and cross-link inhomogeneity of phenolic resins prepared via polycondensation phenol formaldehyde under acidic conditions were studied using small- wide-angle X-ray scattering 1 H-pulse nuclear magnetic resonance spectroscopy. solvent-swelling technique was applied for both measurements at the initial stage to enhance local fluctuations density. change in static dynamic structures obtained through observations functions spin–spin relaxation functions, respectively, during reaction indicates presence two different mechanisms formation growth that depend on amount cross-linker. (i) When there is a stoichiometrically insufficient cross-linker, inhomogeneous domains with loosely cross-linked network appear gelation. intradomain reactions become dominant domain degree cross-linking increases by bridging unreacted sites structure (ii) stoichiometric tightly interdomain size incorporating new polymer chains into