On the exotherm of polyacrylonitrile. II. Examination of deuterated polymers

Abstract

A series of a-, /3,P-, and a,P,P-deuterium-labelled acrylonitrile monomers were prepared and polymerized. Secondary deuterium isotope effects on the polymerization and on the pyrolysis reactions that precede carbon fiber formation were observed. When deuterium is in the a-position, the polymerization rate is greater and the molecular weight is higher. It is proposed that either the propagation rate constant or both that constant and the termination rate constant are increased on deuterium substitution. In differential scanning calorimetry, the polyacrylonitrile exotherm occurs at higher temperatures and is narrower when deuterium is substituted at the a-position. On the other hand, the thermal gravimetric analysis activation energy for weight loss of polymer at temperatures below the acrylic exotherm is lower when deuterium is in the a-position, relative to the a-hydrogen polymers. As there is no correlation between the weight loss energy of activation and the various exotherm parameters, the weight loss and the exotherm are considered to be independent events. Examination of the distribution of deuterium substituted ammonia species evolved during 10O-24O0C thermal treatment of the a-and P,P-deuterated polyacrylonitriles provides a clear indication that both the a-and /3-positions are directly involved in hydrogen migration to nitrogen, but the mechanism of ammonia generation remains unclear. 0 1995

Structural Identification of Polyacrylonitrile during Thermal Treatment by Selective 13C Labeling and Solid-State 13C NMR Spectroscopy

“…Up to now, various spectroscopic methods have been used to identify the chemical structures of the residues after the thermal treatment of PAN, including Fourier transform infrared spectroscopy (FT-IR), ,,,,− solid-state nuclear magnetic resonance (ssNMR), ,,,, elemental analysis, ,, X-ray diffraction, , thermal analysis, , pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS), , etc. However, the precise chemical reactions occurring during PAN stabilization under either inert or oxidative conditions are still not well understood. ,, NMR spectroscopy is always considered as a powerful tool in the study of polymer chain structure and dynamics . As the residue obtained from the thermal treatment of PAN is usually an insoluble resin, 13 C ssNMR is suitable to be employed for probing the chemical structural changes .…”

Mass DSC/TG and IR ascertained structure and color change of polyacrylonitrile fibers in air/nitrogen during thermal stabilization

“…It is the precursor material for carbon fiber, an outstanding engineering material. It has been reported1, 2 to undergo chemical reactions in stages on thermal treatment. The following chemical reactions are believed to take place: (1) cyclization of nitrile groups leading to hydronaphthiridine rings (cyclization)3–5; (2) oxidation of hydrogenation leading to a certain degree of aromatization (dehydrogenation)6; and (3) oxidation of hydronaphthiridine rings leading mainly to acridone and some other structure (oxidative reaction) 7.…”

Photoactive Polyacrylonitrile Fibers Coated by Nano-Sized Titanium Dioxide: Synthesis, Characterization, Thermal Investigation

“…Study of the degradation of polyacrylonitrile has been a subject of interest for decades owing to its commercial value for the production of carbon fibers [6][7][8][9][10]. Spectroscopy, including infrared, ultraviolet, solid-state nuclear magnetic resonance (NMR) and x-ray photoelectron spectroscopy (XPS), and thermal analysis, including differential scanning calorimetry (DSC), differential thermal analysis (DTA) and thermogravimetric analysis (TGA), are the common tools in the study of polyacrylonitrile degradation [11][12][13][14].…”

“…Study of the degradation of polyacrylonitrile has been a subject of interest for decades owing to its commercial value for the production of carbon fibers [6][7][8][9][10]. Spectroscopy, including infrared, ultraviolet, solid-state nuclear magnetic resonance (NMR) and x-ray photoelectron spectroscopy (XPS), and thermal analysis, including differential scanning calorimetry (DSC), differential thermal analysis (DTA) and thermogravimetric analysis (TGA), are the common tools in the study of polyacrylonitrile degradation [11][12][13][14].Semiconductor photocatalysis has been gathering much attention recently due to its promising application in chemical conversion and storage of solar energy for solar cells, hydrogen production, refractory pollutants elimination and self-cleaning surface [15][16][17][18].Among various oxide semiconductor photocatalysts, titanium oxide (TiO 2 ) has been proven so far to be the most promising material used for both fundamental research and practical applications. Because of its highly efficient photoreactivity, biological and chemical inertness, cost effectiveness, non-toxicity, and long-term stability against photocorrosion and chemical corrosion, titanium dioxide has been frequently employed in the environmental treatment and purification purposes [18][19][20][21][22].…”