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

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