POLYMERIZATION OF METHYL METHCRYLATE AND ISO-BUTYL METHACRYLATE IN TERNARY EMULSIONS AND MICROEMULSIONS

Abstract

Methyl methacrylate (MMA) and isobutyl methacrylate (iBMA) have been polymerized in ternary oil-in-water emulsions and microemulsions using various type of cationic surfactants, such as, dodecyltrimethylammonium acetate (DTAA), cetyltrimethylammonium bromide (CTAB), cetyltrimethylammonium acetate (CTAA) and octadecyltrimethylammonium chloride (OTAC) In addition, the novel polymerization of MMA in Winsor I systems (WL) has been studied for the first time. Microcmulsion polymerization of MMA and styrene in the presence of C60 has also been investigated The following objectives are to be achieved from this research project: 1. To establish the different nucleation mechanisms in the polymerization of MMA and iBMA in emulsions and microemulsions. Micellar nucleation prevails in microemulsion polymerization for both MMA and iBMA. However, emulsion polymerization of both monomers may involve a combination of micellar, homogeneous and fine monomer-droplet nucleations, but homogeneous nucleation is less probable for iBMA. 2. To explore the Winsor I system for developing a novel polymerization process that produces nano-size ( diameter < 50nm) PMMA latexes with a relatively high weight ratio (>7) of polymer to surfactant. 3. To study the leasibility of making C60-bound PMMA or polystyrene by microemulsion polymerizations Stable PMMA and PiBMA latexes ( 13 ~ 70 nm in hydrodynamic radius) are obtained from emulsion and microemulsion polymerizations initiated by potassium persulfate (KPS). Molecular weights of PMMA and PiBMA are in the range of 2 ~ 8 x 106. Each latex particle containing about one to two polymer chains is obtained from the microemulsion polymerization at 5 wt% MMA using CTAB. But it is about four polymer chains from the emulsion polymerization using the same MMA concentration. The number of polymer chains per latex particle increases to about five for the microemulsion polymerization and nine for the emulsion polymerization at 9 wt% MMA The weak dependency of MMA poIymerization rate on [surfactants]0.18~0.31 and its strong dependency on [KPS]0.82 are observed for the emulsion polymerization. Contrary to the emulsion polymerization, the polymerization rate of MMA is dependent on [surfactants]0.55~0.60 and [KBS]0.33 for the microemulsion polymerization. The rate of iBMA polymerization is dependent on 0.30 and 0.60 power of the CTAB concentration for emulsion and microemulsion polymerization respectively. This is attributed to a significant nucleation in fine emulsified oil droplets in addition to the micellar nucleation for the emulsion polymerization. But the principal polymerization loci for microemulsion are in microemulsion droplets via the micellar entry mechanism for iBMA as well as MMA. Similar polymerization rate dependencies on the surfactant concentrations are found for MMA ( > 5 wt%) and iBMA (>5 wt%) monomers polymerized in both emulsion and microemulsion. Despite the difference in the solubility of MMA and iBMA in the aqueous phase, the principal polymerization loci for both monomers in emulsions and microemulsions are similar. At a lower monomer concentration (3 wt%), negative rate dependencies are observed for microemulsion polymerizations of MMA and iBMA. However, the PiBMA latexes are much more stable than the PMMA latexes. The strong dependency of number particles per mL latex on the surfactant concentration for the polymerization of MMA and iBMA is discussed in conjunction with the continuous nucleation in the aqueous phase. A winsor I like-system (WL) comprises two clear phases: a lower phase of a microemulsion and an upper oil (MMA) phase. The polymerization of MMA in the WL system proceeds only in the microemulsion phase at the expense of the hulk MMA phase This is a novel polymerization method for producing high molecular weights of PMMA (106) with a relatively high weight ratio (8:1) of polymer to surfactant. In WL polymerization, PMMA latex particles of nanosizes (30 - 60 nm in diameter) are rather polydisperse. Factors that affect the polydispersity of PMMA are discussed in terms of the initiator concentration and the interfacial area between the upper MMA phase and the lower microemulsion phase. A constant polymerization rate region is observed in the polymerization of WL system due to the presence of the upper MMA phase which acts as an monomer reservior. The WL polymerization possesses the characteristics of the microemulsion and the emulsion polymerization. The microemulsion polymerization of MMA and styrene in the presence C60 produces C60-capped polymer. The composites exhibit better thermal stability and UV screening efficiency than the pure polymers. The presence of C60 in the microemulsion polymerization of MMA and styrene will only retard the progress of polymerization resulting the formation of low molecular weight polymers.