Thermally responsive particles of poly(benzimidazobenzophenanthroline) modified with poly(N-isopropylacrylamide)

Poly(benzimidazobenzophenanthroline) (BBL) chain ends were substituted with a well-known thermally responsive polymer poly(N-isopropylacrylamide). The resulting polymers showed superior colloidal stability in aqueous dispersions compared to previously reported poly(ethylene oxide) substituted BBL, and in one case, particles were found to be colloidally stable up to 900 mM NaCl concentration. The typical lower critical solution temperature (LCST) behavior of poly(N-isopropylacrylamide) (PNIPAm) in water was partially lost due to the harsh conditions of the chain end substitution reaction but adjusting the pH or ionic strength facilitated thermally induced phase separation of the dispersed polymer particles. After cooling to ambient temperature, the particles could be re-dispersed and their colloidal stability was regained.