pH-Dependent Self-Assembly of Polystyrene-block-Poly((sulfamate-carboxylate)isoprene) Copolymer in Aqueous Media

• Published in: Langmuir 2008-10, Vol.24 (20), p.12017-12025
• Main Authors: Uchman, Mariusz, Procházka, Karel, Štěpánek, Miroslav, Mountrichas, Grigoris, Pispas, Stergios, Špírková, Milena, Walther, Andreas
• Format: Article
• Language: English
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Materials: Nano-and Mesostructured Materials, Polymers, Gels, Liquid Crystals, Composites; Micelles. Thin films; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Surface physical chemistry
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la8025842

The amphiphilic polystyrene-block-poly((sulfamate-carboxylate)isoprene) (PS-PISC) diblock copolymer was synthesized from the precursor diblock copolymer polystyrene-block-isoprene by reaction with chlorosulfonyl isocyanate. The structure and behavior of self-assembled PS-PISC nanoparticles was studied in alkaline and acidic aqueous solutions by a combination of static and dynamic light scattering, analytical ultracentrifugation, atomic force and cryogenic transmission electron microscopies, NMR spectroscopy, potentiometric titration, and fluorometry using pyrene as a polarity-sensitive fluorescent probe. It was found that PS-PISC exists in aqueous solutions in the form of micellar aggregates. The aggregation tendency increases with decreasing effective charge density in the shell, that is, with decreasing pH of the solution, and aggregates found in alkaline aqueous media have much smaller molar masses than those formed in acidic media. The latter are dense, collapsed structures with immobile PISC domains in which most of the COOH and NH2 +SO3 − groups are buried inside of the nanoparticles. The swelling of PISC domains and disentanglement of PISC chains after addition of a base are slow processes occurring on the time scale of days.