Effect of carbon nanotubes on free radical polymerization of N-isopropylacrylamide in supercritical carbon dioxide and in methanol.

Effect of carbon nanotubes (CNT) on free radical polymerization of N -isopropylacrylamide (NIPAAm) initiated by azobisisobutyronitrile at 55 °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 × 10 6 g/mol but that of PNIPAAm in MeOH was 0.3 × 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. [ABSTRACT FROM AUTHOR]