Physiologically relevant, pH-responsive PEG-based block and statistical copolymers with N,N-diisopropylamine units

Abstract

In order to impart pH-responsiveness within a physiologically-relevant context to PEG-based biomaterials, a new tertiary amine containing repeat unit, N,N-diisopropyl ethanolamine glycidyl ether (DEGE), was developed and incorporated into statistical and block copolymers with ethylene oxide (EO), and allyl glycidyl ether (AGE) via anionic ring-opening polymerization. The reactivity of this novel monomeric building block in copolymerizations with EO was investigated by spectroscopy with observed reactivity ratios of r_DEGE = 1.28 ± 0.14 and r_EO = 0.82 ± 0.10. It was further demonstrated that DEGE containing copolymers could serve as building blocks for the formation of new pH-responsive materials with a pK_a of ca. 9, which allowed macroscopic hydrogels to be prepared from symmetric triblock copolymers PDEGE_5.3k-b-PEO_20k-b-PDEGE_5.3k. The triblock copolymers exhibited clear sol-to-gel transitions in a physiologically-relevant critical gelation range of pH 5.8–6.6 and pH-dependent viscoelastic properties. On the nanometer scale, the preparation of pH-responsive micro- or nanogels was demonstrated by crosslinking P(DEGE-co-AGE) copolymers in miniemulsion droplets stabilized by PEO-b-P(DEGE-co-AGE) diblock terpolymers. These nanoparticles exhibited a reversible pH-dependent swelling profile with a volume phase transition at physiological pH 6.5–7.5.