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

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

doi:10.1039/c9ra01849b

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.

Highlights

Polymerized ionic liquids or poly(ionic liquid)s (PILs), a subclass of polyelectrolytes with ionic moieties as the repeating unit, have attracted much attention due to their combination of properties from both ionic moieties and neutral polymers.[1]
The second approach is via direct polymerization of ionic liquid monomers through conventional free radical polymerization,[8,9,10,11,12] controlled radical polymerization (CRP)[13,14,15,16,17,18,19,20,21,22,23,24,25,26,27] and polycondensation,[28,29] by which major PILs have been prepared
Scheme 1 outlines the synthesis of P[VBMI][BF4]-b-PNIPAM by sequential reversible addition–fragmentation chain-transfer (RAFT) polymerization, in which the initial synthesis of P[VBMI][BF4] by solution RAFT polymerization under [[VBMI] [BF4]]0 : [DDMAT]0 : [AIBN]0 1⁄4 60–270 : 3 : 1 and the subsequent synthesis of P[VBMI][BF4]-b-PNIPAM by solution RAFT polymerization under [NIPAM]0 : [P[VBMI][BF4]]0 : [AIBN]0 1⁄4 360–1200 : 3 : 1 are included

Summary

Introduction

Incorporation of ionic liquid moieties into the appending groups of neutral polymers.[3,4,5,6,7] this method suffers from the nonquantitative metathesis reactions and the polymer is usually contaminated by a tiny fraction of halides.[6]. The aqueous solution of P[VBMI][BF4]-b-PNIPAM does not become turbid even at temperature above PTT of the PNIPAM block, the soluble-to-insoluble phase transition of the PINIPAM block is con rmed by dynamic light scattering (DLS) analysis and variable temperature 1H NMR analysis. This abnormal thermoresponse of P[VBMI][BF4]-bPNIPAM is different from those of ILBCs and is ascribed to the formation of small-sized micelles. Average size of formed micelles was obtained by analyzing more than 100 nanoparticles using the ImageJ so ware

Results and discussion

Conclusions

Conflicts of interest