Energy Transfer and Activated Chemiluminescence during Thermal Oxidation of Polypropylene:  Evidence for Chemically Induced Electron Exchange Luminescence

Abstract

The mechanism of chemiluminescence (CL) during thermal oxidation of polypropylene (PP) was probed by doping PP with an energy acceptor (9,10-dibromoanthracene [DBA]) and a chemiluminescence (CL) activator (9,10-diphenylanthracene [DPA]). Doping PP with DBA had little effect on the shape of the CL intensity (I CL)−time profile. This suggests that energy transfer from triplet states is probably not significant in the scheme of PP CL. However, the CL activator (DPA) had a significant effect on the shape and intensity of the I CL−time profile. In the absence of DPA, the I CL−time profile matches the profile for the formation of carbonyl-containing oxidation products from FTIR-emission spectra. In contrast, in the presence of DPA, it was the integrated DPA I CL−time profile which matched the oxidation product profile, indicating that now I CL was proportional to the hydroperoxide concentration. It is suggested that peroxides formed during PP oxidation are capable of reacting with DPA to produce chemically induced electron exchange luminescence (CIEEL). It is also suggested that CL from undoped PP, i.e., direct CL, may also occur by a CIEEL mechanism. This mechanism is believed to involve the reaction of PP peroxides with an easily oxidizable luminescent oxidation product. For the detector system used in this study the majority of light emitted is consistent with reactions between acyl peroxides and α,β-unsaturated carbonyls. The consequences of this mechanism are that the I CL−time curve measured during the oxidation of PP may reflect either the hydroperoxide profile or the oxidation product profile depending on the spectral wavelength analyzed or the state of purity of the polymer.

Use of 9,10-diphenylanthracene as a contrast agent in chemiluminescence imaging: The observation of spreading of oxidative degradation in thin polypropylene films

“…Another issue of concern might be the effect of DPA on the oxidation mechanism. In a previous study we have compared the rates of oxidation of doped and undoped PP using a DSC-CL apparatus and found that small amounts of DPA did not have a measurable effect on the rate of degradation [21].…”

“…Some of the films were doped with DPA (Aldrich), this was achieved by swelling the films in a concentrated solution of DPA in a 1:1 mixture of AR heptane and AR chloroform. In a previous study [21] we determined that by using this method the concentration of DPA in PP reached a level of 2 Â 10 À3 mol kg À1 . The fact that DPA is distributed homogeneously in the films is indicated by a constant maximum CL intensity regardless of the position in the film where it is measured.…”

“…In a previous publication we demonstrated that a CL signal with a significantly greater intensity was obtained from polymer samples doped with low levels of 9,10-diphenylanthracene (DPA) [21]. Furthermore, it was demonstrated that the luminescence observed followed a different profile compared with CL intensity (I CL )etime profiles of undoped, pure PP and that DPA-enhanced CL was directly proportional to the concentration of peroxides in the sample.…”

“…In previous publications we proposed that the primary light-emitting reaction during oxidation of unstabilised and undoped PP was the reaction between acyl peroxides and certain carbonyls, and that CL intensity (I CL )etime profile of pure PP represents the accumulation of secondary oxidation products, such as carbonyls [20,21]. More recently, Jacobson has reported that this is also true for the thermal oxidation of ultra high molecular weight polyethylene which is of high purity and additive-free [22,23].…”

Accelerating effect of poly(methyl methacrylate) on rubber oxidation, Part 1: A chemiluminescence study

“…Historically, most authors have attributed it to the termination reaction of peroxyl radicals [15,16] or directly to decomposition of hydroperoxides [17,18]. More recently it has been suggested that CL may arise from, or be moderated by interactions with impurities or deliberately added reagents, acting as CL activators [19][20][21][22]. However, despite the fact that the detailed mechanism of CL emission is uncertain, its intensity has been shown to correlate with oxidation as measured by oxygen uptake [23] accumulation of oxidation products (hydroperoxides, carbonyl) [12,[24][25][26][27] or failure time in oven ageing [28].…”