Core-First Synthesis and Thermoresponsive Property of Three-, Four-, and Six-Arm Star-Shaped Poly(N,N-diethylacrylamide)s and Their Block Copolymers with Poly(N,N-dimethylacrylamide)

Abstract

A series of three-, four-, and six-arm star-shaped poly(N,N-diethylacrylamide)s (s-PDEAM3, s-PDEAM4, and s-PDEAM6, respectively) and PDEAM-block-poly(N,N-dimethylacrylamide)s (s-(PDEAM-b-PDMAM)3,4,6 and s-(PDMAM-b-PDEAM)3,4,6) were synthesized by the core-first group transfer polymerization using core initiators possessing three, four, and six silyl ketene acetals, respectively. The thermoresponsive property of s-PDEAM was compared with that of a linear PDEAM (l-PDEAM), and that of s-(PDEAM-b-PDMAM) and s-(PDMAM-b-PDEAM) was compared with that of linear di- and triblock copolymers, l-PDEAM-b-PDMAM, l-PDEAM-b-PDMAM-b-PDEAM, and l-PDMAM-b-PDEAM-b-PDMAM. Both aqueous solutions of s-PDEAM and s-(PDEAM-b-PDMAM) exhibited lower critical solution temperatures (LCSTs), which were characterized using the cloud point (Tc). For the s-PDEAM with different weight average molecular weights (Mw,MALSs), Tc very slightly changed within 1.0 °C. The thermoresponsive behavior of s-(PDEAM-b-PDMAM) is basically similar to those of l-(PDEAM-b-PDMAM) and l-(PDEAM-b-PDMAM-b-PDEAM). The aqueous solution of s-(PDMAM-b-PDEAM) first shows an LCST-type and then an upper critical solution temperature (UCST)-like (actually not UCST) phase transition, that is, the two-stage phase transition. These thermoresponsive behaviors are confirmed using hydrodynamic radii (Rhs) by dynamic light scattering measurements.