Phototunable Cloud Point Temperatures Stemming from Cyclic Topology: Synthesis and Thermal Phase Transition Behavior of Cyclic Poly(N‐acryloylsarcosine methyl ester)

Cyclic polymers possess distinct properties compared with their linear counterparts, such as smaller hydrodynamic volume, lower viscosity, and higher glass‐transition temperature, etc. To explore the impact of the cyclic topology on the thermo‐induced phase transition behavior of poly(N‐acryloylsarcosine methyl ester) (PNASME), the anthracene‐terminated telechelic PNASMEs are synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization of monomer NASME using a bifunctional chain transfer agent (CTA) with two anthryl groups. Subsequently, cyclic PNASMEs are prepared via UV‐induced cyclization under 365 nm UV. There are considerable increases (up to 50 °C) for the cloud point temperatures (Tcps) of cyclic PNASMEs compared with the linear counterparts. In view of the increment, the Tcp of PNASME is tuned by varying the cyclic/linear ratio (the molar ratio between cyclic PNASME and linear PNASME in the product) with different irradiation time. Thermoresponsive cyclic poly(N‐acryloylsarcosine methyl ester) (PNASME) is synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization and UV‐induced cyclization. It is found that the Tcp of the cyclic PNASME is much higher than its corresponding linear counterpart. Encouraged by this fact, the Tcp of PNASME is easily and efficiently tuned in a wide range of temperature (32.3–80.9 °C) by changing the cyclic/linear ratios.