Effect of carbon nanotubes (CNT) on free radical polymerization of N-isopropylacrylamide (NIPAAm) initiated by azobisisobutyronitrile at 55 degrees C in supercritical carbon dioxide (scCO(2)) of 27.6 MPa and in methanol (MeOH) was investigated. The weight average molecular weight (M-w) of PNIPAAm polymerized in scCO(2) for 10 h was 1.2 x 10(6) g/mol but that of PNIPAAm in MeOH was 0.3 x 10(6) g/mol as determined by the intrinsic viscosity. Yield of the polymerization for 10 h in scCO(2) was higher than that in MeOH. Gel permeation chromatography was not effective for molecular weight characterization of PNIPAAm, with a higher M-w giving a larger discrepancy as compared to the viscometric method. PNIPAAm of higher M-w as prepared in scCO(2) giving more chain entanglements that could enhance formations of intrachain and interchain hydrogen bonds resulted in a decrease of the lower critical solution temperature of PNIPAAm. CNT reduced yield but raised M-w of PNIPAAm much more in scCO(2) than in MeOH, an indication that radical scavenging efficiency of CNT in the precipitation polymerization of NIPAAm in scCO(2) was higher than that in the solution polymerization of NIPAAm in MeOH. (C) 2015 Elsevier B.V. All rights reserved.