Synthesis and thermoresponsive property of end‐functionalized poly(<i>N</i>‐isopropylacrylamide) with pyrenyl group

Abstract

Abstract N –Isopropylacrylamide (NIPAM) was polymerized using 1‐pyrenyl 2‐chloropropionate (PyCP) as the initiator and CuCl/tris[2‐(dimethylamino)ethyl]amine (Me 6 TREN) as the catalyst system. The polymerizations were performed using the feed ratio of [NIPAM] 0 /[PyCP] 0 /[CuCl] 0 /[Me 6 TREN] 0 = 50/1/1/1 in DMF/water of 13/2 at 20 °C to afford an end‐functionalized poly( N ‐isopropylacrylamide) with the pyrenyl group (Py–PNIPAM). The characterization of the Py–PNIPAM using matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry provided the number–average molecular weight ( M n,MS ). The lower critical solution temperature (LCST) for the liquid–solid phase transition was 21.7, 24.8, 26.5, and 29.3 °C for the Py–PNIPAMs with the M n,MS 's of 3000, 3400, 4200, and 5000, respectively; hence, the LCST was dramatically lowered with the decreasing M n,MS . The aqueous Py–PNIPAM solution below the LCST was characterized using a static laser light scattering (SLS) measurement to determine its molar mass, M w,SLS . The aqueous solutions of the Py–PNIPAMs with the M n,MS 's of 3000, 3400, 4200, and 5000 showed the M w,SLS of 586,000, 386,000, 223,000, and 170,000, respectively. Thus, lowering the LCST for Py–PNIPAM should be attributable to the formation of the PNIPAM aggregates. The LCST of 21.7 °C for Py–PNIPAM with the M n,MS of 3000 was effectively raised by adding β‐cyclodextrin (β‐CD) and reached the constant value of ∼26 °C above the molar ratio of [β‐CD]/[Py–PNIPAM] = 2/1, suggesting that β‐CD formed an inclusion complex with pyrene in the chain‐end to disturb the formation of PNIPAM aggregates, thus raising the LCST. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1117–1124, 2006