pH-Responsive Diblock Copolymers Prepared by the Dual Initiator Strategy

Diblock copolymers poly(tetrahydrofuran- b - tert -butyl acrylate) (PTHF- b -PtBA) and poly(tetrahydrofuran- b -1-ethoxyethyl acrylate) (PTHF- b -PEEA) were successfully synthesized by the dual initiator 4-hydroxybutyl-2-bromoisobutyrate (HBBIB). The isobutyrate and alcohol function of HBBIB were used for the atom transfer radical polymerization of tBA (or EEA) and the living cationic ring-opening polymerization of THF, respectively. Hydrolysis or thermolysis of the aforementioned diblock copolymers results in amphiphilic pH-responsive copolymers PTHF- b -poly(acrylic acid) (PTHF- b -PAA). Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and nuclear magnetic resonance spectroscopy ( 1 H NMR) were used to analyze the PTHF macroinitiator, while clear evidence for the formation of well-defined block copolymer structures was obtained by 1 H NMR, gel permeation chromatography (GPC), and infrared spectroscopy (FT-IR). The amorphous PtBA block in PTHF- b -PtBA resulted in a decrease of the crystallinity and the melting point of PTHF, as shown by differential scanning calorimetry (DSC). Self-assembly of PTHF- b -PAA copolymers in water into aggregates and micelles when exposed to specific pH values was confirmed by dynamic light scattering, infrared, and NMR spectroscopies.