Novel polymeric composites from microemulsions

Abstract

A novel approach to prepare composites of different porosity and morphology is demonstrated. Instead of blending two polymers, hydrophilic and hydrophobic monomers are solubilized in microemulsions and then polymerized to obtain composites with the desired properties. This technique is exemplified by the polymerization of microemulsions containing styrene and acrylamide as the hydrophobic and hydrophilic monomer, respectively. Different types of surfactants were used in formulating the microemulsions: anionic sodium dodecyl sulfate (SDS), cationic cetyltriethylammonium bromide (CTAB) and zwitterionic octadecyl dimethyl betaine (C18DMB). The clear or bluish microemulsions were stable at room temperature and at the polymerization temperature of 55°C. No gross phase separation was observed during polymerization. The morphology and thermal behaviour of the composites resulting from microemulsion polymerization are strongly influenced by the surfactant, which is trapped inside the solid. C18DMB produced the largest pore size and most rigid composite. Use of SDS or CTAB led to a random copolymer, poly(styrene- co-acrylamide), with a single glass transition temperature ( T g) of 151 ± 2°C, which is intermediate between the T g values of the two homopolymers. The composite obtained using C18DMB was more heterogeneous, with polystyrene-rich and polyacrylamide-rich domains in addition to the copolymer. The T g values of the polystyrene-rich (89 ± 1°C) and polyacrylamide-rich (171 ± 1°C) domains are lower than those of the corresponding homopolymers (99 ± 1°C and 175 ± 1°C, respectively). Apparently, C18DMB acts as a plasticizer in the composite.