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

Abstract

Beyond traditional polymer stabilization, sterically hindered piperidine derivatives move into new application areas where radical functions are key elements. Recent achievements in using nitroxyl derivatives in degradation, polymerization and grafting processes are discussed together with the involved chemical reactions and the resulting material properties. The examples shown cover selected nitroxylethers (NORs) performing as flame retardants and flame retardant synergists or replacing peroxides in manufacturing controlled rheology polypropylene (PP). Furthermore, NORs and nitroxyl radicals mediate radical polymerization processes resulting in tailor-made intermediates for polymer modification via radical and condensation steps and offer access to complex polymer architecture. .

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

“…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.…”

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

“…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.…”

Synergistic Fire Retardancy of Bis(1‐methoxy‐2,2,6,6‐tetramethylpiperidin‐4‐yl)sebacate and Tris(2,4,6‐tribromophenoxy)‐1,3,5‐triazine/Sb2O3 in HIPS

“…As the concentration of NORSM in sample-6 was only 0.50 wt%, no pyrolysis product of NORSM in sample-6 was detected. Compared with sample-2, no tribromophenol but bromophenol was found in the pyrolysis products of sample-6, which indicated that NORSM could promote the decomposition of TTBPC and the release of bromine free radicals, which was similar to the phenomenon described in the literature [23,[47][48][49]. Although NORSM itself can pyrolyze to CO 2 , its concentration is very small; therefore, the marked content increase of CO 2 from 1.68 wt% to 7.27 wt% indicated that NORSM could obviously promote the decomposition of the triazine ring in TTBPC.…”

Effect and mechanism of N-alkoxy hindered amine on the flame retardancy, UV aging resistance and thermal degradation of intumescent flame retardant polypropylene

“…However, with the further increasing of NOR116, the LOI value of the flame retardant PP decreased gradually and the UL-94 only classed a V-2 rating, which was consistent with the inverse concentration effect reported in Cao's work [6]. These could be explained by that when being heated, NOR116 could generate four kinds of free-radicals, i.e., nitroxyl radicals, alkyl radicals, aminyl radicals and alkoxy radicals [14]. The nitroxyl radicals could quench the active freeradicals and reduce their concentration in the gas phase, thus effectively improved the flame retardancy of the mixtures.…”

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

“…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.…”

Synergistic Fire Retardancy of Bis(1‐methoxy‐2,2,6,6‐tetramethylpiperidin‐4‐yl)sebacate and Tris(2,4,6‐tribromophenoxy)‐1,3,5‐triazine/Sb2O3 in HIPS

“…As the concentration of NORSM in sample-6 was only 0.50 wt%, no pyrolysis product of NORSM in sample-6 was detected. Compared with sample-2, no tribromophenol but bromophenol was found in the pyrolysis products of sample-6, which indicated that NORSM could promote the decomposition of TTBPC and the release of bromine free radicals, which was similar to the phenomenon described in the literature [23,[47][48][49]. Although NORSM itself can pyrolyze to CO 2 , its concentration is very small; therefore, the marked content increase of CO 2 from 1.68 wt% to 7.27 wt% indicated that NORSM could obviously promote the decomposition of the triazine ring in TTBPC.…”

Effect and mechanism of N-alkoxy hindered amine on the flame retardancy, UV aging resistance and thermal degradation of intumescent flame retardant polypropylene

“…However, with the further increasing of NOR116, the LOI value of the flame retardant PP decreased gradually and the UL-94 only classed a V-2 rating, which was consistent with the inverse concentration effect reported in Cao's work [6]. These could be explained by that when being heated, NOR116 could generate four kinds of free-radicals, i.e., nitroxyl radicals, alkyl radicals, aminyl radicals and alkoxy radicals [14]. The nitroxyl radicals could quench the active freeradicals and reduce their concentration in the gas phase, thus effectively improved the flame retardancy of the mixtures.…”

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

“…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.…”

Synergistic Fire Retardancy of Bis(1‐methoxy‐2,2,6,6‐tetramethylpiperidin‐4‐yl)sebacate and Tris(2,4,6‐tribromophenoxy)‐1,3,5‐triazine/Sb2O3 in HIPS

“…As the concentration of NORSM in sample-6 was only 0.50 wt%, no pyrolysis product of NORSM in sample-6 was detected. Compared with sample-2, no tribromophenol but bromophenol was found in the pyrolysis products of sample-6, which indicated that NORSM could promote the decomposition of TTBPC and the release of bromine free radicals, which was similar to the phenomenon described in the literature [23,[47][48][49]. Although NORSM itself can pyrolyze to CO 2 , its concentration is very small; therefore, the marked content increase of CO 2 from 1.68 wt% to 7.27 wt% indicated that NORSM could obviously promote the decomposition of the triazine ring in TTBPC.…”

Effect and mechanism of N-alkoxy hindered amine on the flame retardancy, UV aging resistance and thermal degradation of intumescent flame retardant polypropylene

“…However, with the further increasing of NOR116, the LOI value of the flame retardant PP decreased gradually and the UL-94 only classed a V-2 rating, which was consistent with the inverse concentration effect reported in Cao's work [6]. These could be explained by that when being heated, NOR116 could generate four kinds of free-radicals, i.e., nitroxyl radicals, alkyl radicals, aminyl radicals and alkoxy radicals [14]. The nitroxyl radicals could quench the active freeradicals and reduce their concentration in the gas phase, thus effectively improved the flame retardancy of the mixtures.…”