Synthesis and characterization of water insoluble copolymers from diallyldimethylammonium hexafluorophosphate

Abstract

Poly(diallyldimethylammonium chloride) (PDADMAC) is a cationic, water-soluble polymer important for numerous industrial applications. The polymer is prepared through the radical cyclopolymerization of diallyldimethylammonium chloride (DADMAC) in water or other polar solvents. Copolymerization has traditionally been accomplished with water-soluble comonomers to alter the copolymer properties. However, the inherent water solubility of DADMAC polymers prevent the materials from being used as water resistant films and membranes. The work herein seeks to develop DADMAC copolymers that incorporate the cationic moiety and hydrophobic components for use as water insoluble materials. This research exploits the discovery that DADMAC monomer and PDADMAC polymers can be made water insoluble by anion exchange of the chloride counterion to that of the hydrophobic hexafluorophosphate (PF6). The resulting PF6 salt form further makes the monomer or polymers organic soluble, allowing copolymerization with hydrophobic monomers in polar aprotic solvents. Two distinct approaches were pursued in this research: (1) radical copolymerization of DADMA(PF6) monomers with hydrophobic comonomers; (2) step growth copolymerization of end-functional PDADMA(PF6) oligomers to make multiblock copolymers. Copolymers of DADMA(PF6) and methyl methacrylate were synthesized via a radically initiated bulk polymerization. The copolymers were successfully synthesized over a range of comonomer feed ratios, and, at high conversion, excellent incorporation of both monomers was observed. The resulting cationic copolymers cast free-standing films that were entirely insoluble in water. To produce block copolymers, telechelic PDADMA(PF6) oligomers were synthesized using functionalized reagents that act as radical initiators, chain transfer agents, and terminators (iniferters). Based on the functionality, the oligomers were suitable for incorporation as blocks into polysulfones, aromatic polyamides, and polyimides. The relative amounts of the PDADMA(PF6) in all types of block copolymer was tuned by changing the monomer feed ratio. While all copolymers formed water insoluble, free-standing films, their properties were closely tied to both the backbone functional groups and composition. Preliminary characterization demonstrates that the new materials have the potential in applications as modified polyelectrolyte films and membranes.