High-efficiency synthesis of well-defined cyclic poly(N-vinylcaprolactam) and its solution properties

Abstract Well-defined cyclic poly( N -vinylcaprolactam) ( c -PNVCL) was successfully synthesized by a combination of atom transfer radical polymerization (ATRP), supramolecular self-assembly and “selective” click cyclization at a relatively high concentration (10 mg/mL). α-Alkyne- ω -chloro heterodifunctional PNVCL precursor ( l -PNVCL- Cl ) was synthesized by ATRP of N -vinylcaprolactam (NVCL), followed by its conversion to α-alkyne- ω -azido heterodifunctional PNVCL ( l -PNVCL- N 3 ) via nucleophilic substitution reaction with NaN 3 . The intramolecular cyclization of l -PNVCL- N 3 by “selective” click reaction in aqueous micellar media afforded well-defined and narrow-disperse c -PNVCL (PDI = 1.11). The target polymer and intermediates were characterized by GPC/MALLS, 1 H NMR, and FT-IR. The thermoresponsive property of c -PNVCL and its linear precursor ( l -PNVCL- N 3 ) was studied and compared by turbidity and dynamic light scattering (DLS) measurements, and furthermore, their self-assembly behavior was investigated by fluorescence spectroscopy and transmission electron microscopy (TEM). Cyclic poly( N -vinylcaprolactam) can self-assemble to form smaller spherical micelles in aqueous solution and possesses lower critical solution temperature (LCST) and narrower thermal phase transition range in comparison with its linear analogue.