Modulation of the pH-responsive properties of poly(l-lysine iso-phthalamide) grafted with a poly(ethylene glycol) analogue

A pH responsive pseudopeptide, poly(l-lysine iso-phthalamide), has been modified with a hydrophilic poly(ethylene glycol) analogue, Jeffamine M-1000® and the effect of grafting ratio on the pH responsive behaviour of the grafted polymers in aqueous solution investigated using fluorescence and 1H NMR spectroscopy. It was demonstrated that at below 35.1 wt% grafting, the modified polymers retained the pH-driven conformational transition of the parent polymer from an expanded structure at high degrees of ionisation to a compact hydrophobically stabilised structure at low degrees of ionisation. The onset of pH response and the pH range over which the conformational transition occurred varied significantly with degree of grafting. At Jeffamine M-1000® ratios in excess of 48.0 wt%, the graft polymer existed in a micellular form over the whole pH studied. Potential applications in drug delivery of both the linear and micellular forms are discussed.