Abstract
A novel polymeric emulsifier， SSIPM modified tetracarboxylic acid terminated polyester (SMTAPE)was prepared by end-capping sulfopolyester polyol with TMA in this study. The surface characteristics of SMTAPE， the optimum hydrophobic length of SMTAPE for the emulsion polymerization of PBMA， the nucleation mechanism and the surface area occupied by a SMTAPE molecule on a polymer latex particle at room temperatuve were studied by analyzing the surfactant characteristics， the reaction kinetic and the stability of the latices， the consumption of SMTAPE emulsifier during emulsion polymerization and the adsorption behavior of SMTAPE on polystyrene latices.The SMTAPE emulsifier is surface active， lowering the surface tension of water by about 15 mN/m at the cmc.Experimental results also indicate that SMTAPE emulsifiers with a shorter average hydrophobic length stabilize the PBMA latex by the depletion mechanism. Although possessing good mechanical stability， using those emulsifiers have a higher coagulum during the synthesis stage. However， the SMTAPE emulsifiers with a longer average hydrophobic length anchor strongly on the PBMA latex particles and stabilize them by an electrotatic force with a negligible amount of steric stabilization. Although possessing better synthesis stability， using these emulsifiers have a poor mechanical stability. Results presented herein also confirm that the SMTAPE emulsifiers with optimum hydrophobic length can anchor latex particles and show steric stabilization mechanism with good synthesis and mechanical stability.Futhermore， according to the experimental results， formation of the subsequent PBMA latex is attributed to a coagulation process of particle precursors， micellar particles as well as existing PBMA latex particles.The effect of the stirring speed and the amount of emulsifier on the kinetics and particle size distribution were studied to obtain more quantitative evidence for the nucleation mechanism in this system. The experimental results from the kinetic studies and the emulsifier consumption clearly showed that a continuous nucleation mechanism with no Smith-Ewart interval II present were the characteristics of this system. this was attributed to the high concentration of SMTAPE emulsifier in the polymerization， which led to a large surface area and vast number of ~10nm micelles which served as the major locus of particle nucleation and the nucleation period lasted well into the reaction until the disappearance of the micelles or the disappearance of monomer droplets. A broad particle size distribution was oberved thoughout the reaction.The surface area occupied by a SMTAPE molecule on a PS latex particle at 25℃ was found to be 187 at saturation. The conformation of SMATAPE emulsifier molecule adsorbed on a PS latex particle is thought to be a hydrophobic segment “trains” anchored to the polymer surface.