What will happen when thermoresponsive poly(N-isopropylacrylamide) is tethered on poly(ionic liquid)s?

Guangmei Luo; Yakun Guo; Chonggao Liu; Guang Han; Xiaodong Ma; Wangqing Zhang

doi:10.1039/c9ra01849b

What will happen when thermoresponsive poly(N-isopropylacrylamide) is tethered on poly(ionic liquid)s?

RSC Adv. 2019 Apr 26;9(23):12936-12943. doi: 10.1039/c9ra01849b. eCollection 2019 Apr 25.

Authors

Guangmei Luo¹, Yakun Guo¹, Chonggao Liu¹, Guang Han², Xiaodong Ma³, Wangqing Zhang^{1

4}

Affiliations

¹ Key Laboratory of Functional Polymer Materials of the Ministry of Education, Institute of Polymer Chemistry, College of Chemistry, Nankai University Tianjin 300071 China wqzhang@nankai.edu.cn +86-22-23503510.
² State Key Laboratory of Special Functional Waterproof Materials, Beijing Oriental Yuhong Waterproof Technology Co., Ltd Beijing 100123 China hanguang@yuhong.com.cn.
³ School of Energy and Environmental Engineering, Hebei University of Technology Tianjin 300401 China.
⁴ Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Nankai University Tianjin 300071 China.

Abstract

The thermoresponsive ionic liquid diblock copolymer of poly[1-(4-vinylbenzyl)-3-methylimidazolium tetrafluoroborate]-block-poly(N-isopropylacrylamide) (P[VBMI][BF₄]-b-PNIPAM) containing a hydrophilic poly(ionic liquid) block of P[VBMI][BF₄] is prepared by sequential reversible addition-fragmentation chain transfer (RAFT) polymerization. This P[VBMI][BF₄]-b-PNIPAM exhibits an abnormal thermoresponsive phase transition at a temperature above the phase transition temperature (PTT) of the PNIPAM block. For P[VBMI][BF₄]-b-PNIPAM including a short P[VBMI][BF₄] block, its aqueous solution becomes turbid at a temperature above the PTT of the thermoresponsive PNIPAM block, whereas for P[VBMI][BF₄]-b-PNIPAM containing a relatively long P[VBMI][BF₄] block even in the case of a relatively long PNIPAM block, the aqueous solution remains transparent at a temperature far above the PTT of the PNIPAM block, although a soluble-to-insoluble phase transition of the PINIPAM block is confirmed by dynamic light scattering (DLS) analysis and variable temperature ¹H NMR analysis. The reason that P[VBMI][BF₄]-b-PNIPAM exhibits an abnormal thermoresponse is discussed and ascribed to the highly hydrophilic and charged poly(ionic liquid) block of P[VBMI][BF₄] leading to the formation of small-sized micelles at a temperature above the PTT.