Nitroxyl radicals and nitroxylethers beyond stabilization: radical generators for efficient polymer modification

Pfaendner, Rudolf

doi:10.1016/j.crci.2006.08.001

Cited by 56 publications

(53 citation statements)

References 5 publications

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“…Furthermore, after 1680 h of irradiation no cracks were observed on the surface of the specimen. The long induction period of the photo-oxidation of the composite is in agreement with the reported literature [27][28][29][30] which has proposed the hypotheses that within polymer matrix, NOR HAS are readily converted to nitroxide radicals which scavenge alkyl radicals. Then, the formed alkoxyamines do subsequently react with peroxy radicals to regenerate the active nitroxide radical.…”

Section: Resultssupporting

confidence: 80%

Effects of sterically hindered N-alkoxyamines on photooxidative stability of reinforced polypropylene

Enescu

Frache

2012

E-Polymers

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Abstract:In the present paper the influence of Flamestab ® NOR TM 116 (abbrev. FNOR), a sterically hindered N-alkoxyamine stabilizer, on the photo-oxidative stability of calcium carbonate reinforced polypropylene (abbrev. CCPP) used for production of plastic collars has been investigated. The samples, prepared by melt compounding, were exposed to artificial accelerated photo-ageing carried out at λ>300 nm and 45 o C in air. FT-IR and UV-VIS analysis revealed that the deterioration of neat CCPP takes place very rapidly in comparison with the composites containing FNOR. Hydroperoxides and various carbonyl species are formed as the main degradation products during the photo-oxidation process. Moreover, the intensity of the absorption bands grows with increasing of UV exposure time indicating that the material suffers a photo-oxidative degradation process. Indeed, addition of only 0.1 wt.-% FNOR did not significantly modify the length of the induction period of neat CCPP, but a strong efficiency was obtained by increasing the amount of FNOR (0.5 wt.-%) which shows an increase of eight times more as compared with neat CCPP. Therefore, it may be supposed that OIT is linked to the level of concentration of the stabilizer. This remarkable increase in composite stability demonstrated by a lengthening of OIT is typical for sterically hindered N-alkoxyamine stabilizers since they are very efficient at scavenging freeradicals formed as the polymer degrades. In other words, these UV stabilizers are converted to nitroxide radicals (see Scheme 1) which readily trap the polymer degradation species to produce alkoxyamines. Then, the formed alkoxyamines do subsequently react with peroxy radicals to regenerate the active nitroxide radical, thereby this process (called Denisov cycle) proceed in a regenerative cycle, thus retarding oxidative polymer degradation. The increase of absorbance in the carbonyl region as a function of irradiation time was used to determinate the photooxidation rate. It was found out that the photooxidation rate measured from the slope of linear part of the curves is significantly decreased for the CCPP/FNOR0.5 composite compared to neat CCPP. In the light of the above mentioned findings, FNOR could be taken into consideration as an UV stabilizer for CCPP.

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Section: Resultssupporting

confidence: 80%

Effects of sterically hindered N-alkoxyamines on photooxidative stability of reinforced polypropylene

Enescu

Frache

2012

E-Polymers

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“…Even without any additional flame retardant, it was demonstrated that alkoxyamines alone can achieve flame retardancy, e.g. in polypropylene fibers and films [15,16]. Meanwhile, various structures and process patents have been published that claim alkoxyamines to be efficient flame retardants [17,18].…”

Section: Introductionmentioning

confidence: 99%

Design and Utilization of Nitrogen Containing Flame Retardants Based on N-Alkoxyamines, Azoalkanes and Related Compounds

Wilén

Pfaendner

2014

Polymer Green Flame Retardants

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“…From the viewpoint of flame retardancy of polymers mainly radical generators triggered by thermolysis or redox systems have been successfully used to suppress and retard the fire response of polymeric materials [21,22]. In the past it has been demonstrated that certain peroxides can be used as synergists to enhance the action of brominated flame retardants (BFR) [23][24][25][26][27][28][29], whereas azo compounds [30] and alkoxyamines [12,31] have been shown to provide self-extinguishing properties to polymers even by themselves. Thus, it has been established that radical precursors that are capable of generating various carbon (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…Various radical generators based on different substance classes have had undoubtedly an impact on both polymer chemistry and have played an important role in many different fields of natural sciences. In particular, free radicals are involved in polymer degradation [11][12][13][14], controlled free radical polymerization [15], grafting processes [16], cross-linking of polymers and chemical reactions (cyclizations, additions, decarboxylation) [17] and wide applications in biochemistry [18]. It is well known, that free radicals are also important (and influence ignition, heat release, flame propagation and/or flame quenching) as intermediates in the combustion reactions of various materials and the flammability of a given material is strongly dependent on the concentration of free radicals [19].…”

Section: Introductionmentioning

confidence: 99%

Disulfides – Effective radical generators for flame retardancy of polypropylene

Pawelec

Holappa

Tirri

et al. 2014

Polymer Degradation and Stability

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The potential of thirteen aliphatic, aromatic, thiuram and heterocyclic substituted organic disulfide derivatives of the general formula R-S-S-R' as a new group of halogen-free flame retardants (FR) for polypropylene films have been investigated. According to DIN 4102-1 standard ignitibility test, for the first time it has been demonstrated that many of the disulfides alone can effectively provide flame retardancy and self-extinguishing properties to polypropylene (PP) films at already very low concentrations of 0.5 wt%. In an effort to elucidate the mechanism of the thermal decomposition of disulfide derivatives the fragmentation patterns of the evolved gases from a thermogravimetric analyzer (TGA) have been analyzed by simultaneous mass spectrometry (MS) and Fourier transform infrared spectrometry (FTIR). The main decomposition products initiated by homolytic scission of the S-S bond and/or scission of the C-S bond were identified as thiols, aliphatic and aromatic hydrocarbons, isothiocyanates (depending on the disulfide structures) with further evolution of elemental sulfur and sulfur dioxide at temperatures of above 300 o C and 450 o C, respectively. Based on this preliminary study, we have shown that disulfides represented by e.g. diphenyl disulfide (1), 5,5'-dithiobis(2-nitrobenzoic acid) (2), bis(1-phenyl-1H-tetrazol-5yl)-disulfide (4), 2-bisbenzothiazole-2,2′-disulfide (6) and N,N-dithiobis-(phtalimide) (10) constitute a new halogen-free family of additives for flame retarding of polypropylene.

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Nitroxyl radicals and nitroxylethers beyond stabilization: radical generators for efficient polymer modification

Cited by 56 publications

References 5 publications

Effects of sterically hindered N-alkoxyamines on photooxidative stability of reinforced polypropylene

Effects of sterically hindered N-alkoxyamines on photooxidative stability of reinforced polypropylene

Design and Utilization of Nitrogen Containing Flame Retardants Based on N-Alkoxyamines, Azoalkanes and Related Compounds

Disulfides – Effective radical generators for flame retardancy of polypropylene

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