Grafting of functional nitroxyl free radicals to polyolefins as a tool to postreactor modification of polyethylene‐based materials with control of macromolecular architecture

Abstract

Nitroxyl radicals were used as functionalizing agents during the free radical postreactor modification process of polyolefins carried out in the melt. The 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl (HO‐TEMPO) and the 4‐benzoyloxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl (BzO‐TEMPO) free radicals were successfully grafted onto a polyethylene‐based material (ethylene‐co‐1‐octene copolymer) by coupling reaction with polymer macroradicals; these last were formed by H‐abstraction through peroxide addition. The macromolecular structure of the functionalized polyolefins was assessed by 1H‐NMR, FTIR spectroscopy, and SEC measurements which were used to evidence the grafting site, to evaluate the grafting level and to highlight the occurrence of chain extension through crosslinking side reactions. Indeed the use of proper model compounds allowed the preparation of accurate FTIR calibration curves for the quantitative determination of the functionalization degree. Besides the high temperature SEC analysis highlighted that this fast and simple coupling reaction between macroradicals and nitroxyl free radicals grants the grafting of functionalities onto the polyolefin backbone by contemporarily preventing the side reactions liable of the structure and MW modification of the pristine polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Effect of nitroxyl-based radicals on the melt radical grafting of maleic anhydride onto polyethylene in presence of a peroxide

“…3a) clearly shows signals between 0.5 and 2.5 ppm and a broad signal at 3.8 ppm. The signals in the range 0.5 and 2.5 ppm can be attributed to the PE backbone while the signal at 3.8 ppm is attributed to grafted TEMPO and in particular to the proton located onto the PE backbone in the alpha position with respect to the grafted nitroxide, as discussed by Cicogna et al [46]. By comparison of the signals of the TEMPO moiety at 3.8 ppm and the PE backbone in the range 0.5-2.5 ppm, the grafting yield of TEMPO was found to be approximately 37% (0.589 TEMPO for 1000 ethylene units = 0.33 wt.% of grafted TEMPO calculated from Fig.…”

Absorption and Emission Spectra of a Flexible Dye in Solution: A Computational Time-Dependent Approach

“…This compound is interesting because of its potential application in the design of "smart" polymers with mechanochromic attributes as proven by the experimental characterization obtained through spectroscopic techniques and reported in a recent paper. [52][53][54] More specifically, the 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO) unit was used, in combination with functionalizing groups such as hydroxyl, benzyl, naphthyl (HO-, BzO-and NfO-TEMPO), for grafting the fluorescent probe to polyethylene derivatives via post-reactor modification. 52,53 The NfO-TEMPO derivative, substituted with a methyl group at the grafting site, has been studied from both experimental and theoretical points of view in toluene solution.…”

“…[52][53][54] More specifically, the 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO) unit was used, in combination with functionalizing groups such as hydroxyl, benzyl, naphthyl (HO-, BzO-and NfO-TEMPO), for grafting the fluorescent probe to polyethylene derivatives via post-reactor modification. 52,53 The NfO-TEMPO derivative, substituted with a methyl group at the grafting site, has been studied from both experimental and theoretical points of view in toluene solution. 53,54 The theoretical analysis 54 depicted a complex conformational landscape, containing six stable conformers, characterized by different values of the three flexible dihedral angles describing the relative orientation of the naphthyl moiety and the TEMPO ring system (see Figure 2).…”

Structural, dynamic and photophysical properties of a fluorescent dye incorporated in an amorphous hydrophobic polymer bundle

“…In order to demonstrate its efficiency, this improved multi-level approach has been applied to the study of a specific dye, namely 4-naphtoyloxy-1-methoxy-2,2,6,6-tetramethylpiperidine (NfO-TEMPO) grafted onto an apolar polymer matrix, which was investigated experimentally by Passaglia and co-workers. 32,33 The behavior of this dye in toluene solution and its spectroscopic properties were already studied through a combination of theoretical and experimental methodologies and the results were reported and exhaustively discussed in a previous paper. 30 It turned out that maximum absorption and emission wavelengths, spectral line shapes and Stokes shifts were very well reproduced by the proposed computational protocol, which was based on a time-dependent statistical description of the whole system represented by explicit molecules.…”