A Study of Deuterium Distribution in Deuterated Polyolefins by Pyrolysis−Photoionization Mass Spectrometry

Abstract

The saturation of polydienes with deuterium produces labeled polyolefins that, when studied with the identical hydrogenated polydienes, have proven quite useful for the understanding of many of the basic properties of these materials. However, until now the only way to determine the amount of deuterium substitution on the labeled molecules has been to compare the densities of the hydrogenated and deuterated polymers, which gives no information on how the deuterium is distributed along the chains. The information is important, since it is clear from the density results that with some saturation catalysts (Pd) there must be some H-D exchange since there are more than two deuterium atoms per diene monomer on the labeled species, while for others (Wilkinson's) there appears to be no exchange. In this work, pyrolysis-photionization mass spectrometry has been used to examine the structure of the hydrogenated and deuterated polydienes in more detail. The deuterium distributions were determined using a modified Bernoullian model that takes into account the first two D's that were added by the saturation event. The most revealing data come from the tetramer C 4H8-xDx, which confirm the average level of deuteration as measured by density. For polymers saturated with Pd catalysts, the pyrolysisphotionization mass spectra show that the deuterium was randomly distributed by the H-D exchange. Perdeuteriopolyisobutylene was also examined, as was its blend with hydrogenous polyisobutylene, which helped to confirm that exchange had occurred during the saturation of the polydienes using the catalyst rather than during the measurement step. The data for the polydiene deuterated using Wilkinson's catalyst confirmed that there was little, if any, exchange.

Regularity of Deuteration in Linear Polyethylene Prepared by Saturation of Polycyclopentene over Homogeneous Catalysts

“…On the other hand, if the unbinding rate is high and Rh–HD equilibrates with D 2 to release HD and form Rh–D 2 , a net positive H/D exchange and a DL above 20% would result. A DL of 20.1% for dPE–Rh suggests that Rh–HD unbinding is slow and that elimination reactions mostly lead to H/D scrambling, consistent with what has been found by pyrolysis-photoionization mass spectrometry . Of course, low levels of exchange between hydrides bound to the catalyst and reducing gases dissolved in solution (D 2 , HD, or H 2 ) are not ruled out by this analysis.…”

“…/D scrambling, consistent with what has been found by pyrolysis-photoionization mass spectrometry 25. Of course, low levels of exchange between hydrides bound to the catalyst and reducing gases dissolved in solution (D 2 , HD, or H 2 ) are not ruled out by this analysis.…”

“…Experimentally, Bond and Hillyard have shown that cis -2-pentene isomerizes to 1-pentene and trans -2-pentene during hydrogenation over Wilkinson’s catalyst at one-third of the hydrogenation rate . Moreover, with polybutadiene saturated with D 2 over Wilkinson’s catalyst, Zoller et al showed via pyrolysis-photoionization mass spectrometry the presence of H/D interchange (“scrambling”) between mers, concluding that the deuteration is not entirely regular . Analogous H/D scrambling during the deuteration of cycloalkenes had been previously reported. , While these studies indicate that the deuteration of double bonds over Wilkinson’s catalyst can involve isomerization and consequent H/D scrambling, there has been only limited investigation into the mechanism and extent of these side reactions.…”

Vacuum Ultraviolet Photoionization Mass Spectra and Cross-Sections for Volatile Organic Compounds at 10.5 eV

“…VUV-SPI is a soft ionization technique that can be adjusted to be nearly fragmentation free. Thus, recently VUV-SPI-TOFMS has been applied to diagnose several systems such as automobile exhaust gas, [3][4][5][6] pyrolysis of polymers [7][8][9][10][11] and coals, 12 flue gas, 13,14 cigarette smoke, 11,[15][16][17] silicon chemical vapor deposition, [18][19][20][21][22] and aerosol particles. 23 A coherent VUV laser light at 10.5 eV (118 nm) generated by a frequency tripling of the third harmonics (355 nm) of a Nd:YAG laser is a good photoionization light source due to the easy generation and high intensity.…”

“…Thus, VUV light at 10.5 eV has been used as the photoionization source of molecules. 3,4,[7][8][9][10][11][12][13]15,[20][21][22][23][24][25][26][27][28] When the photoionization cross-sections for VOCs are known, quantitative detection becomes possible by comparison with intensities from the standard sample. Although photoionization efficiency curves for many molecules have been reported, the data of the absolute photoionization cross-sections of VOCs are very limited.…”