In situ gelling aqueous solutions of pH- and temperature-sensitive poly(ester amino urethane)s

A series of novel pH- and temperature-sensitive multiblock poly(ester amino urethane)s were synthesized. The copolymers were characterized by 1H NMR, FT-IR and GPC. In the multiblock copolymers, the tertiary amino groups of the poly(amino urethane) segments act as pH-responsive moieties, while the PCL–PEG–PCL blocks act as biodegradable and temperature-sensitive segments. At a relatively high pH (7.0 or above), the multiblock copolymer aqueous solution showed a sol-to-gel-to-aggregation transition with increasing temperature. In contrast, at a lower pH (below 7.0), the polymer solution always existed as a sol state within the experimental temperature range. The gel window covers the physiological conditions. After subcutaneous injection of the 20 wt% multiblock copolymer solutions into mice, polymeric hydrogels were formed in situ in a short time. The in vitro release of an anticancer drug, paclitaxel, persisted over 1 month under physiological conditions.