SUMMARY:The thermal degradation mechanisms of poly [2,29-bis(3,4-dicarboxyphenoxy)phenylpropane-2-phenylenediimide] (PEI) have been investigated by thermogravimetry (TG) and by direct pyrolysis mass spectrometry (DPMS). TG data show that PEI has a main decomposition step centred at about 510 8 C followed by a less marked step in the 600 -650 8 C temperature range and leaving about 60% of charred residue at 800 8 C. The total ion curve (TIC) of a purified PEI sample, obtained by DPMS, closely reproduces the two maxima appearing in the derivative TG (DTG) curve, whereas the TIC curve of a crude PEI sample shows two less pronounced maxima in the temperature range of 250 -450 8 C due to low molar mass compounds, which volatilize undecomposed in the high vacuum of the MS. The structure of the pyrolysis compounds obtained in the first thermal degradation step of a purified PEI sample suggest that they are mainly formed by the scission of: i) the isopropylidene bridge of bisphenol A; ii) the oxygen-phthalimide bond; iii) the phenyl-phthalimide bond, which are apparently the weakest bonds of PEI. Extensive hydrogen transfer reactions and subsequent condensation reactions may account for the high amount of char residue. The pyrolysis compounds obtained in the second degradation step (620 8 C) are mainly constituted of CO 2 , benzene, aniline, benzonintrile, phenylenediamine, and dibenzonitrile, which may be generated by further thermal degradation reactions of pyrolysis compounds containing N1H phthalimide as end groups. Another degradation processes which may account for CO 2 formation is the hydrolysis of the imide moiety to form poly(amic acid) units which produce an aromatic amide structure by decarboxylation. The pyrolysis of an aromatic polyamide (NOMEX) was then studied for comparison. The structure of the pyrolysis products detected by the DPMS analysis of both polymers allowed a detailed schematization of the thermal degradation pathways involved in the degradation of PEI and on the reactions leading to the formation of the charred residue.

No abstract

No abstract

Matrix-assisted laser desorption ionization mass spectrometry (MALDI-TOF-MS) has been found to be an excellent method to determine the structure of the molecules produced in the photooxidative degradation of poly(butylene succinate) (PBSu) at 60 °C in air. Over 20 compounds are present in the MALDI spectrum of the oxidized sample, as compared to only 4 in the original PBSu sample. The MALDI spectra present many new well-resolved peaks, which provide information on the structure and end groups of the oxidation products. The MALDI peaks correspond to sodiated ions of oxidized oligomers, and they have been assigned to polymer chains containing succinic and malonic acid, butyl ester, ethyl ester, and butyl formate end groups. These oligomers had not been revealed before. The mechanisms accounting for the formation of photooxidation products of PBSu involve the operation of several reactions:  (i) oxidation of hydroxyl end groups; (ii) α-H abstraction decomposition; (iii) Norrish I photocleavage. Our results establish the photooxidation mechanisms of PBSu. The novelty of our approach consists of using a nonaveraging technique, such as mass spectrometry, which allows the detection of individual compounds formed during the oxidation process. This is a remarkable result, and it should be expected that future MALDI studies might have an impact on the current views on photooxidation processes of other polymer systems.

No abstract