Threonine-based chiral homopolymers with multi-stimuli-responsive property by RAFT polymerization

- This work presents the controlled synthesis of temperature- and pH-sensitive homopolymer having chiroptical property by RAFT polymerization.
- The LCST-type transition temperature (40-60 °C) could be tuned by the pH-value (pH = 3-10), and it increased remarkably by the addition of the urea.
- Well-defined polymers having different chirality and hydrophilicity were also synthesized, which have affected the dual stimuli-responsive and chiroptical properties.

Temperature- and pH-sensitive homopolymer having chiroptical property was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of a threonine-containing acrylamide, N-acryloyl-l-threonine (A-(L)Thr-OH), followed by methylation. The LCST-type thermoresponsive property of poly(A-(L)Thr-OMe) was observed in aqueous solutions, and the transition temperature could be changed remarkably by pH value. The addition of urea also led to the increase in the transition temperature, suggesting that the hydrogen-bonding is a crucial factor to manipulate the thermoresponsive properties. Well-defined polymers having different chirality and hydrophilicity, poly(A-(D)Thr-OMe) and poly(A-(L)Ser-OMe), were also prepared from N-acryloyl-d-threonine (A-(D)Thr-OH) and N-acryloyl-l-serine (A-(L)Ser-OH). We evaluated the effects of pH, urea, and salt in aqueous solutions, and hydrophobicity, chirality, and molecular weights of the resulting polymers on the dual stimuli-responsive and chiroptical properties.

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