Association Behavior of Poly (methyl methacrylate-b-methacrylic acid-b-methyl methacrylate) in Aqueous Medium

—ABA type tri-block amphiphilic polyelectrolyte consisting of poly(methyl methacrylate-block-methacrylic acid-block-methyl methacrylate) (P(MMA-b-MAA-b-MMA)) was synthesized by atom transfer radical polymerization technique (ATRP) and the self-assembly behavior of the polymers in aqueous solution was studied over the course of neutralization. Combination of potentiometric and conductometric titrations along with dynamic light scattering (DLS) techniques were used to investigate the size and shape of aggregates at various degrees of neutralization. The effect of hydrophobic-hydrophilic (MMA-MAA) ratio and polymer chain length on the aggregation behavior during neutralization was studied. P(MMA-b-MAA-b-MMA) with longer MMA segment self-assembles via the close association mechanism through stronger self-entanglement of MMA chains, whereas P(MMA-b-MAA-b-MMA) with shorter MMA chain self-assembles via the open association mechanism, as confirmed by transmission electron microscopy (TEM). Conductometric titration was used to determine the counterion condensation during the course of neutralization. When the charge density of micelle approaches a critical value as neutralization progresses, counterion condensation of Na+ ions on the polymer chains occurs. The effect of counterion condensation on the aggregation behavior during neutralization was elucidated. Index Terms—laser light scattering, MMA-b-MAA-bMMA, potentiometric titration, self-assemble Manuscript received October 23, 2003. Kam C. Tam is with MEBCS of Singapore-MIT Alliance, and School of Mechanical and Production Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798 (phone: 6567905590; e-mail: [email protected]) Jia Yao is with the MEBCS of Singapore-MIT Alliance, 50 Nanyang Avenue, Singapore, 639798 (e-mail: [email protected]). Palaniswamy Ravi is with the MEBCS of Singapore-MIT Alliance, 50 Nanyang Avenue, Singapore, 639798 (e-mail: [email protected]). Leong H. Gan is with the Natural Science, National Institute of Education, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798 (e-mail: [email protected]).