Polymer reactions. VI. Inhibited autoxidation of polypropylene

Abstract

SynopsisThe autoxidation of polypropylene inhibited by 2,6-di-tertbutyl-pcresol (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 welldefined induction period duFing which the ROO. concentration is estimated to be lo-* 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 lO71./molesec. at 130°C. At the end of the induction period, [ROOH], [ROO.], and --d[Oz] /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. I n all systems where the oxidation rates were appreciably suppressed there was formed a very stable paramagnetic species, S., which was inert toward AH and IZ but reactive toward triethyl phosphite. Because of its similarity with spin centers in carbon black, Sis postulated to be a delocalized polysulfide spin center. With both S and'AH p y e n t , the combined effect of stabilization is synergistic. The obsemed time-dependent variations of [ROOH], [ROO.], and [A.] follow familiar mechanisms. Mathematical relationships describing each of these three systems are included.

The origins of volatile oxidation products in the thermal degradation of polypropylene, identified by selective isotopic labeling

“…The labeling observations derived in this GC/MS study correlate well with the findings reported in our recent paper on the C-13 NMR identification of solid-phase oxidation products in this same set of selectively-labeled PP samples, which showed methyl ketones derived exclusively from C(2), acids and esters from both C(1) and C (2), and with the preponderance of products (w80e85%) involving oxidation chemistry at the C(2) carbon atom. Unlike the solid-phase products, however, we have found small amounts of volatile products involving oxidation of the C(3) methyl carbon.…”

Photostabilization of Polymers

“…286,355 End-of-pulse transient absorption spectroscopy of 2,6-di-tert.-butylp-cresol (Topanol OC) (8.3) shows the formation under UV irradiation of phenoxy radicals, which can further decay by three bimolecular processes, namely:98.696 286,355 End-of-pulse transient absorption spectroscopy of 2,6-di-tert.-butylp-cresol (Topanol OC) (8.3) shows the formation under UV irradiation of phenoxy radicals, which can further decay by three bimolecular processes, namely:98.696…”

ESR Spectroscopy in Polymer Research

“…A number of workers recorded the ESR studies of radiation-produced peroxy radicals of polypropylene 332,[456][457][458]603,623,683,684,838,1034,1154,1158,1159,1330,1476,1481,1591,1639,1648,1560,1651,2243) ESR spectra of peroxy radicals produced by 'Y-irradiation of polypropylene in the presence of oxygen at room temperature and at 77 K are asymmetric and do not show any distinct dependence upon temperature (Fig. 7.6).…”