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

Abstract

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 (SKA^Et) as the initiator. The B(C₆F₅)₃-catalyzed group transfer copolymerization (GTcoP) of iPMAm and N,N-dimethylacrylamide (DMAm) with SKA^Et was used for the synthesis of statistical, diblock, and triblock copolymers, such as PiPMAm_x-stat-PDMAm_y, PiPMAm_x-b-PDMAm_y, and PiPMAm_x/2-b-PDMAm_y-b-PiPMAm_x/2 and PDMAm_y/2-b-PiPMAm_x-b-PDMAm_y/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 (T_c), hydrodynamic radius (R_h), and ¹H NMR spectroscopy measurements. The T_c for PiPMAm_x 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 T_c increased with the increase of the DMAm-unit in the copolymer and the degree of T_c change for PiPMAm-stat-PDMAm was greater than that for PiPMAm-b-PDMAm, PiPMAm_x/2-b-PDMAm_y-b-PiPMAm_x/2, and PDMAm_y/2-b-PiPMAm_x-b-PDMAm_y/2.