Synthesis And Rheological Behaviour Of Dendritic Hydrophobically Modified Acrylic Emulsion Thickener

Two novel amphiphilic dendron-coil macromonomers-3,5-di(n-hexadecyloxy) benzoyloxy polyoxyethylene methacrylate (F2) and3,4,5-tri(n-hexadecyloxy) benzoyloxy polyoxyethylene methacrylate (F3) was synthesized by esterification of polyoxythylene (molecular weight M=1000) with3,4,5-tri(n-hexadecyloxy) benzoyl chloride and3,5-di(n-hexadecyloxy) benzoyl chloride, then followed by methacrylate chloride. The compounds were characterized by means of NMR and FT-IR, elementary analysis.TR-70was chosen as emulsifier, APS as initiator, then emulsion polymerization method was used to copolymerize MAA and EA with the F2, F3and stearyl alcohol polyoxyethylene methacrylate (F1) to get a series of highly efficient emulsion thickners with a low initial viscosity:1) different F2contents (wt%):0,3.5,5.17,10.5;2) different MAA contents (wt%):20%,30%,40%;3) different function monomers:the mole ratio is F1:F2:F3=6:3:2.We studied the rheological behaviors of the synthetic emulsions:the steady shear rate viscosity and frequency dependent behaviors. The results indicated that a steep rise of thickening viscosity occurred when the pH value increased to about6.5. We also investigated the effects of F2content, MAA, solid content and different function monomer on rheological behavior of thickening systems. The results showed that the increasing F2content improved the thickening efficient by conformation of the network structure. And the zero-shear viscosity increased with the rising of MAA and solid contents. We kept the total number of hydrophobic alkyl tails constant then found that the viscosity of the thickener system increased as the rising of hydrophobic alkyl tails number although the mole number of the function monomers decreased.We studied the internal structure of thickener systems through determining the variation of G’ and G" with angular frequency at constant temperature. The results were as follows:1) The G’ was less than G" within all the angular frequency when the ratio of F2was0%at different pH values. But when we add10.5%F2we found that G;>G" when the pH value higher than6.2and this mean that the thickener system had formed impeccable hydrophobic associating network.2) The G’ was less than G" when the solid content was0.5%. When we increased the solid content, both the G’ and G" were rising, but the G’ increased faster than the G" and finally the G’>G". It meant that the hydrophobic associating network became more and more integrate as the rising of solid content.3) If we kept the F2at5.17%and the pH value at7.8, we found the G’ was always higher than G" when the MAA content was changed. It indicated that all the samples were formed network structure. However the G’ was not various with the angular frequency when the content of MAA was higher than30wt%. It showed that the hydrophobic associating network became more and more integrate as the rising of MAA content.4) We kept the total number of hydrophobic alkyl tails constant, we find that the G’ increased as the rising of hydrophobic alkyl tails number although the mole number of the function monomers decreased. For the latex C and H, the G’ was not various with the angular frequency. This phenomenon meant that the effective hydrophobic associating crosslinking spots increased with the rising of hydrophobic alkyl tails, so the network structure was integrated.The results demonstrated for the first time the potential of this novel amphiphilic dendron-coil macromonomer in hydrophobically modified alkali-soluble emulsion copolymer and associative thickeners in the further.