Thermoresponsive Behaviors of Core-Crosslinked Star Polymers Composed of Amino Acid-Derived Vinyl Polymers in an Aqueous Solution

Abstract

Amino acid-derived vinyl polymers are of great interest as bio-based thermoresponsive soft materials with diverse applications in the industrial, biomedical, and cosmetic fields. In this study, 14 distinct core-crosslinked stars (CCS) polymers are synthesized by reversible addition–fragmentation chain transfer polymerization of N-acryloyl amino acid (X)-methyl esters (X = alanine, β-alanine, or glycine), followed by a core–gel approach. These CCS polymers have the following systematic variations in their molecular architecture: i) three types of amino acid-based polymer arms with the same chain lengths but different arm numbers, ii) different combinations of amino acid species in the arm and core segments, and iii) heteroarm composition (i.e., miktoarm type). All CCS polymers are water-soluble and exhibited lower critical solution temperature (LCST) behaviors. The thermal responses are strongly dependent on structural factors, such as arm species (hydrophobicity), arm number, and polymer shape. The transition temperatures of the CCS polymers are lower than those of the corresponding linear polymers with almost the same molecular weight, particularly when the arm polymers has relatively high hydrophilicity. Furthermore, tunable LCST behaviors (20–55 °C) are achieved for miktoarm-type CCS polymers by adjusting heteroarm composition. These findings provide useful insights into the thermoresponsive behaviors of bio-based CCS polymers.