A Water Dispersible Nanocomposite of Polyacrylonitrile with Silica via Aqueous Polymerization of Acrylonitrile by K2CrO4–NaAsO2 Redox System

Abstract

ABSTRACT:The aqueous polymerization of acrylonitrile initiated by the redox pair, potassium chromate-sodium arsenite produced polyacrylonitrile which was recovered as a coagulum in the medium. A simple procedure was developed for obtaining a stable suspension of polyacrylonitrile-SiO 2 nanocomposite by conducting the polymerization in presence of SiO 2 as a particulate dispersant. SEM analyses revealed distinct morphological features of the polyacrylonitrile-SiO 2 nanocomposite. TEM analyses indicated the particle sizes of the polyacrylonitrile-SiO 2 composite to be in the 28-100 nm range. TG analyses revealed the enhanced thermal stability of the polyacrylonitrile-SiO 2 nanocomposite relative to that of the base polymer polyacrylonitrile. 20 developed a suspension polymerization technique using combination of water and appropriate nonaqueous solvents (for the monomers) in presence of usual oxidants to produce the corresponding nanocomposites.A significant recent development in this direction was the application of emulsion polymerization technique by Choi et al. [21][22][23][24] for the formation of nanocomposites of both speciality polymers (PANI, PPY) and the fundamental polymers (polystyrene, polyacrylonitrile, and copolymers thereof) with Na + -MMT clay. Inverted emulsion pathway was recently described by Choi et al. 25 for the preparation of intercalated PPY/Na + -MMT nanocomposite.In the above background, we wish to report in this article a simple procedure of preparing a PAN-SiO 2 nanocomposite via aqueous polymerization of AN by Cr 6+ /AsO 2 − redox pair in presence of nanodimensional silica as particulate dispersants. The scope of this procedure is fairly wide since a variety of acrylic monomers and combinations thereof may be employed in presence of suitable particulate dispersants for the fabrication of the respective nanocomposites. We shall also describe some relevant bulk properties such as morphology, thermal stability, conductivity, and water dispersibility of the PAN-SiO 2 nanocomposite. EXPERIMENTAL Materials and MethodsAcrylonitrile (Aldrich, USA) was freed from inhibitors by successive washings with dilute sodium carbonate solution, dilute sulfuric acid and finally with distilled water. It was kept over-night over calcium chloride and distilled in an all glass apparatus. The fraction boiling at 77-78 • C was collected and stored carefully. Potassium chromate (Riedel, Germany) and sodium arsenite (Riedel, Germany) were used as the oxidant and the reductant respectively. SM-30 Colloidal (30% weight suspension in water, density 1.22 g mL −1 ) SiO 2 (Aldrich, USA) was used as the particulate dispersant. All other solvents were of analytical grade and were freshly distilled before used. Polymerization of Acrylonitrile with K 2 CrO 4 -NaAsO 2 Redox SystemIn a Pyrex flask, a definite amount (1.8-3.0 × 10 −3 mol) of K 2 CrO 4 was dissolved in 30 mL distilled water to which 0.02 mol of acrylonitrile was injected. The system was kept under stirring at ambient temperature under N 2 atmosphere for 10 m...

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