Radiation chemical studies on thermosensitive N-isopropylacrylamide and its polymer in aqueous solutions.
The pulse radiolysis technique has been employed to determine the initiation and propagation rates of different transient species involved in the polymerization of N-isopropylacrylamide (NIPA) in aqueous solutions. Polymerization by anionic mechanism has been observed to be faster than by the free-radical mechanism. The kinetic, spectroscopic and redox properties of the transient species formed upon reaction of primary radiolytic species of water radiolysis with NIPA have been evaluated. The one-electron oxidation potential for the formation of a radical cation is quite high (>2 V), but the one-electron reduction potential is low (in the range of -0.3 to -0.7 V). The radical anion of NIPA is able to undergo an electron-transfer reaction with MV(2+), and has a pK(a) value of 3.2. The tert-butyl alcohol radical was also able to initiate polymerization. Gamma radiation-induced polymerization studies showed that the reaction of H(.)/(.)OH/e(aq)(-)/tert-butyl alcohol radicals with NIPA results in a nearly equal yield of the gel fraction. The hydrogel is observed to have very little swelling below pH 3 and above pH 10. The linear polymer of NIPA formed by irradiating dilute aqueous solution is found to be a thermosensitive polymer with lower a critical solution temperature (LCST) of ~33 degrees C. The diameters of polymer molecules were 290 and 20 nm at temperature below and above LCST, respectively.
Acharya
Anjali
A
Radiation Technology Development Section, Bhabha Atomic Reseach Centre, Trombay, Mumbai 400 085, India.
Mohan
Hari
H
Sabharwal
S
S
D000178:Acrylamides / Q000737:chemistry* / Q000494:pharmacology*; D000438:Alcohols / Q000737:chemistry; D000838:Anions; D002412:Cations; D004307:Dose-Response Relationship, Radiation; D004583:Electrons; D005609:Free Radicals; D005720:Gamma Rays; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D011108:Polymers / Q000737:chemistry*; D011675:Pulse Radiolysis; D012996:Solutions; D013053:Spectrophotometry; D013696:Temperature; D014867:Water / Q000737:chemistry*
D000178:Acrylamides; D000438:Alcohols; D000838:Anions; D002412:Cations; D005609:Free Radicals; D011108:Polymers; D012996:Solutions; D014867:Water; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; C067295:N-isopropylacrylamide; D010100:Oxygen