The effect of mole ratio distribution on the physical properties of a polyoxyethylated alkylphenol

Summary It has been shown repeatedly (1, 2, 3) that for polyoxyethylated nonionic surfactants a certain hydrophobe‐hydrophile balance (i.e., average mole ratio of ethylene oxide to hydrophobic material) is necessary to obtain maximum wetting, optimum detergency, etc. A study has been conducted to determine the effect of mole ratio distribution of ethylene oxide on the physical properties of a polyoxyethylated nonylphenol. This was accomplished by molecularly distilling two nonionics: a nonylphenol plus 6.0 moles of ethylene oxide and a nonylphenol plus 9.5 moles of ethylene oxide. The following conclusions have been reached concerning the effect of mole‐ratio distribution on the physical properties of these surfactants. The mole ratio distribution of ethylene oxide in a polyoxyethylated nonylphenol follows the Poisson formula and curve in a manner analogous to the polyoxyethylene glycols (Fig. 1). The hydrophobe‐hydrophile balance of the undistilled surfactant may be altered by molecular distillation. This is accomplished by narrowing the range of molecular species. Wetting which is superior to the undistilled material may be effected by narrowing the distribution of molecular species (Figure 3). Fractions from the distilled surfactant showed slight improvement in initial foam volume at certain mole ratios of ethylene oxide to base material over the undistilled material (Figure 6). No change in foam stability was noted. Although there is an optimum ratio of ethylene oxide to the hydrophobic base at which maximum cotton or wool detergency is obtained, cotton and wool detergency are relatively unaffected by mole ratio distribution (Figure 7). Surface and interfacial tension are also comparatively unaffected by mole ratio distribution change. Emulsifying properties of these materials are adversely affected by narrowing the mole ratio distribution.