Abstract
The intumescent process of sodium (substituted) phenolates has been studied. The generation of hydrogen radical via a homolytic cleavage of the Ar–H bond and the subsequent hydroarylation of phenolates to cyclohexadienes along with cyclization and elimination reactions of cyclohexadienes are critical steps in the base promoted intumescence of phenols. The substituents show great influence on the intumescence of phenolates. Phenolates substituted with a weak electron donating group enable intumescence while those with an electron withdrawing group or strong electron donating group suppresses intumescence. This distinction can be justified by both electronic and steric effects of substituents on the generation of hydrogen radical and the degree of hydroarylation.
Highlights
Intumescence is the formation of expanded carbonaceous char
Our work will be constructive to stimulate the development of catalytic intumescent flame retardants, and help comprehend the substantial effects of alkali on the quality of char produced from the carbonization of biomass and coals [28]
13 C composite pulse decoupled (CPD) Nuclear magnetic resonance (NMR) spectra of sodium phenolates with time at Figure 4. 13C composite pulse decoupled (CPD) NMR spectra of sodium phenolates with time at 495
Summary
Intumescence is the formation of expanded carbonaceous char. It has been a widely-used technique in the flame retardancy of polymeric materials [1,2,3,4]. It acts as a catalyst for the carbonization of charring agents through esterification, elimination, and cyclization reactions [13,14,15,16,17,18], and functions as bridges, together with aliphatic structures, to link the hard polyaromatic stacks [19,20]. These bridges act as soft segments to regulate the viscosity of intumescent materials and are the key to good intumescence [21]. Our work will be constructive to stimulate the development of catalytic intumescent flame retardants, and help comprehend the substantial effects of alkali on the quality of char produced from the carbonization of biomass and coals [28]
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