Synthesis and thermoresponsive property of end-functionalized poly(N-isopropylacrylamide) with pyrenyl group

N-Isopropylacrylamide (NIPAM) was polymerized using 1-pyrenyl 2-chloropropionate (PyCP) as the initiator and CuCl/tris[2-(dimethylamino)ethyl]-amine (Me6TREN) as the catalyst system. The polymerizations were performed using the feed ratio of [NIPAM](0)/[PyCP](0)/[CuCl](0)/[Me6TREN](0) = 50/1/1/1 in DMF/water of 13/2 at 20 degrees 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,M-MS). The lower critical solution temperature (LCST) for the liquid-solid phase transition was 21.7, 24.8, 26.5, and 29.3 degrees 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,M-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,,,SLS. The aqueous solutions of the Py-PNIPAMs with the M-n,M-MS's of 3000, 3400, 4200, and 5000 showed the M-w,M-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 degrees C for Py-PNIPAM with the Mn,MS of 3000 was effectively raised by adding beta-cyclodextrin (beta-CD) and reached the constant value of similar to 26 degrees C above the molar ratio of [beta-CD]/[Py-PNIPAM] = 2/1, suggesting that beta-CD formed an inclusion complex with pyrene in the chain-end to disturb the formation of PNIPAM aggregates, thus raising the LCST. (c) 2005 Wiley Periodicals, Inc.