Thermoresponsive properties of poly(N-isopropyl,N-methylacrylamide) and its statistical and block copolymers with poly(N,N-dimethylacrylamide) prepared by B(C6F5)3-catalyzed group transfer polymerization†
Poly(N-isopropyl,N-methylacrylamide) (PiPMAm) was synthesized to create a new family of thermoresponsive polyacrylamides using the B(C6F5)3-catalyzed group transfer polymerization (GTP) of N-isopropyl,N-methylacrylamide (iPMAm) with 1-methoxy-1-(triethylsiloxy)-2-methyl-1-propene (SKAEt) as the initiator. The B(C6F5)3-catalyzed group transfer copolymerization (GTcoP) of iPMAm and N,N-dimethylacrylamide (DMAm) with SKAEt was used for the synthesis of statistical, diblock, and triblock copolymers, such as PiPMAmx-stat-PDMAmy, PiPMAmx-b-PDMAmy, and PiPMAmx/2-b-PDMAmy-b-PiPMAmx/2 and PDMAmy/2-b-PiPMAmx-b-PDMAmy/2, respectively (the mole fraction of x + y was 100). The living nature of the GTP of iPMAm was confirmed by polymerization kinetics, a chain extension experiment, and characterization of the PiPMAm structure using SEC, MALDI-TOF MS and 1H NMR spectroscopy measurements. The thermal phase transition behavior of PiPMAm and its copolymers with DMAm was evaluated using their aqueous solutions based on the cloud point temperature (Tc), hydrodynamic radius (Rh), and 1H NMR spectroscopy measurements. The Tc for PiPMAmx decreased with the increase of x from 25 to 200 and was ca. 12 °C above the x of 300. For the statistical, diblock, and triblock copolymers, the Tc increased with the increase of the DMAm-unit in the copolymer and the degree of Tc change for PiPMAm-stat-PDMAm was greater than that for PiPMAm-b-PDMAm, PiPMAmx/2-b-PDMAmy-b-PiPMAmx/2, and PDMAmy/2-b-PiPMAmx-b-PDMAmy/2.