ISSN:
0449-296X
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The autoxidation of polypropylene inhibited by 2,6-di-tert-butyl-p-cresol (AH) and dilauryl thiodipropionate (S) was studied by the combined methods of electron spin resonance, oxygen absorption, and chemical analysis. With AH alone, there is a critical concentration of about 6 X 10-3 mole/l. below which there is no inhibition. This critical concentration agrees with that determined for inhibited squalane autoxidation and that calculated from known rate constants. Above the critical concentration there is a well-defined induction period during which the ROO· concentration is estimated to be 10-8 mole/l. [ROOH] decreased rapidly as did [A·] and [AH]; the latter are kinetically related. The rate constant for the reaction between A· and ROO· is estimated to be 7 X 107 l./mole-sec. at 130°C. At the end of the induction period, [ROOH], [ROO·], and -d[O2]/dt increased rapidly until steady-state values were attained for all of them. With S alone, there are only retarded oxidation but no well-defined induction periods. [ROOH] is greatly reduced by S. In all systems where the oxidation rates were appreciably suppressed there was formed a very stable paramagnetic species, S·, which was inert toward AH and I2 but reactive toward triethyl phosphite. Because of its similarity with spin centers in carbon black, S· is postulated to be a delocalized polysulfide spin center. With both S and AH present, the combined effect of stabilization is synergistic. The observed time-dependent variations of [ROOH], [ROO·], and [A·] follow familiar mechanisms. Mathematical relationships describing each of these three systems are included.
Additional Material:
9 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1967.150050717
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