Dendrigraft with citric acid on acrylonitrile/acrylic acid copolymer electrospun fibres

摘要

Acrylonitrile/acrylic acid copolymers were synthesized with different mole fractions (1, 2, 5 and 10 mol%) of acrylic acid (AA) in the feed by aqueous suspension polymerization, and bead-free fibres (295-375 nm in diameter) were made from the copolymers in dimethylformamide solutions by electrospinning. In a heterogeneous system containing electrospun fibre mats, dendritic molecules were grown by reaction between carboxylic acid of AA and-OH groups of citric acid activated by dicyclohexylcarbodiimide. The products were analysed using ~1H NMR, ~(13)C NMR and Fourier transform infrared spectroscopies, density determination, scanning electron microscopy, optical microscopy, differential scanning calorimetry and pH response properties. With decreasing AA content, the isotacticity of the copolymers decreases with a more random distribution of the co-monomers which leads to higher percentage conversions of dendrigraft due to reduced steric hindrance. On the formation of dendrigraft, the percentage conversion of the reactions decreases with an increase of generation number and AA content. A reduction of density for the first generation and then an increase with increasing generation are observed. During oxidation stabilization of fibres with a decrease of AA content and an increase in generation number, the amount of liberated heat increases. Fibres containing more carboxylic groups show significantly greater amounts of swelling/de-swelling in basic and acidic media, respectively. To be used as nanocarbon fibre precursors, or as active particles for loading with guest molecules, or as pH actuators, the first generation of dendrigrafted fibres are expected to have the greatest potential among the various samples examined.