Synthesis and Thermoresponsive Property of Linear, Cyclic, and Star-Shaped Poly(N,N‑diethylacrylamide)s Using B(C6F5)3‑Catalyzed Group Transfer Polymerization as Facile End-Functionalization Method

• Published in: Macromolecules 2016-07, Vol.49 (13), p.4828-4838
• Main Authors: Kikuchi, Seiya, Chen, Yougen, Ichinohe, Eiji, Kitano, Kodai, Sato, Shin-ichiro, Duan, Qian, Shen, Xiande, Kakuchi, Toyoji
• Format: Article
• Language: English
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.6b01075

The syntheses of linear, cyclic, and star-shaped poly­(N,N-diethyl­acrylamide)­s (PDEAAms) have been studied in order to clarify the topological effect on their thermoresponsive properties. For the group transfer polymerization of N,N-diethyl­acrylamide using tris­(pentafluoro­phenyl)­borane (B­(C6F5)3) as the organocatalyst, the α-, ω-, and α,ω-end-functionalizations of the PDEAAms with well-controlled molecular weights and narrow polydispersities were quantitaively produced using the silyl ketene aminals with hydroxyl, ethynyl, and vinyl groups as functional initiators and 2-phenyl acrylate derivatives with hydroxyl, ethynyl, and bromo groups as functional terminators. The ω-end-functionalized PDEAAm with the azido group and the α,ω-end-functionalized PDEAAm with the ethynyl and azido groups were used as the starting materials for the inter- and intramolecular copper­(I)-catalyzed click reactions leading to the 3-armed star-shaped and cyclic PDEAAms (s 3-PDEAAm and c-PDEAAm, respectively). In order to eliminate the unit effect of the triazole (taz) group on the thermoresponsive behavior, the linear PDEAAm with the taz group at the center of the polymer chain (l-taz-PDEAAm) was prepared by the click reaction between the end-functionalized PDEAAm with the ethynyl group and that with the azido group. The thermoresponsive property of these PDEAAms with the DPs of 26–29, 50–52, and 78–80 was evaluated by the cloud point (T c) determined by the turbidity measurements and the enthalpy changes (ΔH) of water molecules per molar monomer unit by highly sensitive differential scanning calorimetry (micro-DSC) measurements. The phase transition behavior of s 3-PDEAAm on the transmittance curve was similar to that of l-taz-PDEAAm, rather than c-PDEAAm. The T c values decreased in the order of l-taz-PDEAAm > c-PDEAAm > s 3-PDEAAm. The ΔH values for s 3-PDEAAm were almost the same as those for c-PDEAAm, which were lower than those for l-taz-PDEAAm.