ISSN:
1022-1352
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
To investigate chain-initiating and crosslinking mechanisms, radical formation in dilute aqueous solutions of N-isopropylacrylamide (NIPAAm) and poly-NIPAAM was studied using electron pulse radiolysis with optical detection at room temperature. Several transients of NIPAAm generated by reactions with electrons, hydroxyl radicals and hydrogen atoms were observed. Electron attachment to the carboxyl group (ke = 9.0 x 109 dm3 · mol-1 · s-1) forms the radical anion, which undergoes fast and reversible protonation (pKa = 7.8) at the carboxyl oxygen. At pH 〉 pKa, slow and irreversible protonation of the electron adduct at the vinyl group leads to the α-carboxyalkyl radical CH3(.CH)CONHCH(CH3)2, which is also formed by addition of H atoms to NIPAAm (kH = 7.3 × 109 dm3 · mol-1 · s-1). Addition of OH radicals (kOH = 5.4 × 109 dm3 · mol-1 · s-1) forms CH2(OH)(.CH)CONHCH(CH3)2. Hydrogen abstraction was not observed in the case of NIPAAm monomer, but it was found for the reaction of OH radicals with thermally polymerized NIPAAm. Semi-empirical quantum chemical calculations support the assignment of the observed spectra to the radicals. A reaction mechanism for the formation of crosslinks is discussed.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
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