Comparative Investigation of the Hydrolysis of Charge-Shifting Polymers Derived from an Azlactone-Based Polymer.

Poly 2-vinyl-4,4-dimethylazlactone (PVDMA) has received much attention as a "reactive platform" to prepare charge-shifting polycations via post-polymerization modification with tertiary amines that possess primary amine or hydroxyl reactive handles. Upon hydrolysis of the resulting amide or ester linkages, the polymers can undergo a gradual transition in net charge from cationic to anionic. Herein, a systematic investigation of the hydrolysis rate of PVDMA-derived charge-shifting polymers is described. PVDMA is modified with tertiary amines bearing either primary amine, hydroxyl, or thiol reactive handles. The resulting polymers possess tertiary amine side chains connected to the backbone via amide, ester, or thioester linkages. The hydrolysis rates of each PVDMA derivative are monitored at 25 and 50 °C at pH values of 5.5, 7.5, and 8.5, respectively. While the hydrolysis rate of the amide-functionalized PVDMA is negligible over the period investigated, the hydrolysis rates of the ester- and thioester-functionalized PVDMA increase with increasing temperature and pH. Interestingly, the hydrolysis rate of the thioester-functionalized PVDMA appears to be more rapid than the ester-functionalized PVDMA at all pH values and temperatures investigated. It is believed that these results can be utilized to inform the future preparation of PVDMA-based charge-shifting polymers for biomedical applications.