Synthesis and characterizations of a novel zwitterionic hybrid copolymer containing both sulfonic and carboxylic groups via sulfonation and zwitterionic process

A novel zwitterionic hybrid copolymer containing both sulfonic and carboxylic groups was synthesized via sulfonation, zwitterionic process and sol–gel reaction. The properties of the step products were characterized by FT-IR spectra, thermal analyses, MALDI measurements and SEM morphologies. FT-IR spectra confirmed the related reactions. TGA and DrTGA analyses showed that their thermal stability enhanced with an increase in the zwitterionic extent. DSC curves revealed that both the glass transition temperature and the melting temperature elevated with the rising content of ion pairs. MALDI measurements suggested that the molecular structure of the zwitterionic hybrid PEG-[Si(OEt)3]2SO3HCOOH was more stable than that of neutral hybrid PEG-[Si(OEt)3]2 or that of negatively charged hybrid PEG-[Si(OEt)3]2SO3H. SEM image of the sulfonated polymer film indicated that the pore size was within 2.4–6.1 μm; whereas SEM of the zwitterionized copolymer film displayed that its pore size was less than 1 μm. This shrinkage in pore size can be ascribed to the introduction of carboxylic groups into the copolymer chains. Compared with that observed in the unionized polymer film, the large difference in the morphology of the ionized copolymer films demonstrated that ionization could alter these copolymer’s characteristics. Due to its excellent pore-creating performance, this zwitterionic hybrid copolymer expects to be employed to prepare nanofiltration and ultrafiltration membranes.