Formation and properties of polymer carbon

Abstract

Divinylbenzene (48%)/ethylvinylbenzene copolymer was converted to a series of pyrolytic derivatives. Enough of the carbon bond network remained intact throughout thermal rearrangement and condensation to retain the original gross shape of the copolymer in the final polymer carbon. Although a carbon residue (6% by weight) was obtained by direct heating of the copolymer, yields were increased eightfold by preoxidation or prechlorination. Such an alteration of thermal degradation is obviously a complex process involving both “inhibition,” in the ordinary sense, and a considerable contribution toward an increased valence network density. As a consequence, the average molecular weight of volatile fragments evolved during carbonization is inversely proportional to the oxygen content of the original hydrocarbon polymer. Pyrolysis of divinylbenzene copolymer, containing 18% oxygen, resulted in a 50% volume shrinkage, 50% weight loss, and a 100% density gain. Unless these data are attributable to extensive microporosity, it is difficult to account for the sorption of up to 3 cc. of helium gas per gram of polymer carbon at 30°C. and 600 mm. pressure; and calculated surface areas as large as 1400 sq.m./g. Abrupt changes in the progress of polymer carbon formation occurred between 600 and 700°C. The residue became rigid; vigorous evolution of volatile products, principally hydrogen, suddenly diminished; and paramagnetic resonance absorption (unpaired electron concentration) dropped about tenfold while d.c. resistivity decreased 106 ohm cm. In this region, also, x‐ray patterns were most diffuse, exhibiting no maxima characteristic of carbon scattering in either hydrocarbons or condensed rings. Finally, the x‐ray patterns of polymer carbon intermediates became less diffuse in samples prepared at 700°C. or above. Yet, scattering indicated the presence of crosslinked graphitic layers of such stability that reordering or true graphitization did not occur at 2400°C.

Multi‐instrument characterization of poly(divinylbenzene) microspheres for use in liquid chromatography: as received, air oxidized, carbonized, and acid treated

“…Winslow et al similarly observed volume shrinkage after the air oxidation of their divinylbenzene/ethylvinylbenzene copolymer. [33] Somewhat unexpectedly, Li and coworkers report no decrease in particle size in a similar process. [29] However, they worked with particles that had a broad size distribution so any change in diameter may have been less obvious than for the particles we employed.…”

“…These surface areas are quite low and not far from the theoretical surface area for the particles (1.91 m 2 /g), which was calculated using a density of PDVB nanoparticles (1.18 g/cm 3 ) reported by Ethirajan et al [35] However, after carbonization at 900°C, the surface area and pore volume of the particles increase dramatically, indicating that the particles had become quite porous. [9,33] Nitric acid treatment did not substantially change the properties of these particles.…”

“…This decrease is resonable as more C-C bonds are formed during the process, and hydrogen is lost. [33] These carbonized PDVB particles were then treated with nitric acid to oxidize their surfaces. After acid treatment, the particle size (3.50 ± 0.06 μm) was similar to that of the carbonized PDVB particles (see Fig.…”

“…Thus, FTIR confirms the oxidation of PDVB and its chemical transformation to an oxidized material when it is heated to 250°C. [29,33] PDVB appears to enjoy good chemical stability to about 100°C. Reasonable stability is suggested to 150°C, although there is already evidence of oxidation at this temperature.…”

“…At 700°C, any FTIR signals attributable to molecular functional groups have disappeared, where these result are consistent with other reports of the carbonization of PDVB. [21,33,41] Also, at 700°C and at 900°C, the particles absorb strongly with decreasing photon energy, that is, decreasing wavenumber. [16,42] For this strongly absorbing carbon, the particles were also probed with an ATR accessory with a germanium crystal.…”