State-of-the-art phosphorylation of water-soluble allyl cellulose via a green radical-mediated “click” reaction pathway with enhanced antifungal activity

Allyl Cellulose (AC) was synthesized using allyl bromide in sodium hydroxide (NaOH)/urea aqueous solution. By employing a molar ratio of 6:1 of allyl bromide/cellulose, low-degree of substitution (DS) water-soluble AC (AC₁) was obtained (DS = 0.67). Then, radical-mediated "click" reactions of AC₁ with diethyl phosphite (DEP) and dibutyl phosphite (DBP) were carried out in deionized water as green reaction medium, using 4,4'-azobis(4-cyanovaleric acid) (ACVA) as a radical initiator. The synthesized AC₁-DEP and AC₁-DBP showed high conversion percentages of 84 % and 87 %, respectively. Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) techniques were used to validate the structure of the products and confirm the successful radical-mediated "click" reactions of AC₁ with dialkyl phosphite (DAP) in water. X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), static contact angle, and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) analyses were used to investigate structural, thermal, and surface properties, revealing an increase in flexibility and hydrophobicity upon phosphorylation. AC₁-diethyl phosphite (AC₁-DEP) and AC₁-dibutyl phosphite (AC₁-DBP) exhibited efficient antifungal activities with inhibition zone ranges from 14 to 27 mm.