Synthesis, characterization, and surface activity of surfactants derived from nonylphenol, ethylene oxide and carbon dioxide

The synthesis of the nonylphenol poly(ethylene carbonate) surfactants derived from nonylphenol (NP), carbon dioxide and ethylene oxide (EO) were carried out with high yields in the presence of alkali metal salts (K2CO3, Na2CO3, K2SnO3 and zinc glutamate) as base catalysts. The synthesis reactions were carried out in a stainless-steel reactor in the temperature range of 150-200 degrees C under an initial pressure of 800 psi, with an initial molar ratio of CO2/EO = 0.21, catalyst concentration of 1 x 10(-3) M for a 24 h-period. The surfactants were characterized by FT-IR and by H-NMR. The percentages of carbon dioxide incorporation were between 7 and 16% indicating that the activation of CO2 is a rather difficult process under the catalytic conditions used (175-200 degrees C and 800 psi of final pressure). It was found that the most probable mechanism for the synthesis of the surfactants occurs in two steps. The first reaction involves the role of the base as a catalyst for the formation of the cyclic ethylene carbonate from CO2 and ethylene oxide. The next step is the reaction of the nonylphenol in the presence of cyclic ethylene carbonate and ethylene oxide to generate the surface active compounds. This mechanism indicates that for each mol of carbon dioxide incorporated, one mol of EO has to be added. The CMC values of the surfactants decrease (from 200 to 100 mM) with the increase in the molar ratio CO2/EO (from 0.08 to 0.3) which can be attributted to a decrease in the hydrophilic character of the surfactant heads due to the addition of carbonate groups (-O-C(=O)-O-) to the ethoxylated chains (between 1 to 3 moles).