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Golub, Morton A.

Publications and source records attributed to Golub, Morton A..

27 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

ESCA Study of Poly (Vinylidene Fluoride) Tetrafluoroethylene - Ethylene Copolymer and Polyethylene Exposed to Atomic Oxygen

The ESCA (electron spectroscopy for chemical analysis) spectra of films of poly(vinylidene fluoride) (PVDF), tetrafluoroethylene-ethylene copolymer (TFE/ET) and polyethylene (PE) exposed to atomic oxygen (O(P-3)), in or out of the glow of a radio-frequency O2 plasma, were compared. ESCA spectra of PE films exposed to (O(P-3)) in low Earth orbit (LEO) on the STS-8 Space Shuttle were also examined. Apart from O(P-3)-induced surface recession (etching), the various polymer films exhibited surface oxidation, which proceeded towards equilibrium saturation oxygen levels. The maximum surface oxygen uptakes for in-glow or out-of-glow exposures were in the order: PE greater than TFE/ET greater than PVDF; for PE itself, the oxygen uptakes were in the order: in glow greater than out of glow greater than LEO. Given prior ESCA data on poly(vinyl fluoride) and polytetrafluoroethylene films exposed to O(P-3), the extent of surface oxidation is seen to decrease regularly with increase in fluorine substitution in a family of ethylene-type polymers. (Keywords: ESCA; poly(vinylidene fluoride); tetrafluoroethylene ethylene copolymer; polyethylene; atomic oxygen; radio-frequency oxygen plasma; low Earth orbit)

Golub, Morton A.↗
NASA NTRS1988

ESCA study of Kapton exposed to atomic oxygen in low earth orbit or downstream from a radio-frequency oxygen plasma

The ESCA spectra of Kapton polyimide film exposed to atomic oxygen O(3P), either in low earth orbit (LEO) on the STS-8 Space Shuttle or downstream from a radio-frequency oxygen plasma, were compared. The major difference in surface chemistry induced by the two types of exposure to O(3P), both of which caused surface recession (etching), was a much larger uptake of oxygen by Kapton etched in the O2 plasma than in LEO. This difference is attributed to the presence of molecular oxygen in the plasma reactor and its absence in LEO: in the former case, O2 can react with radicals generated in the Kapton molecule as it etches, become incorporated in the etched polymer, and thereby yield a higher steady-state 'surface oxidation' level than in LEO.

Golub, Morton A.↗
NASA NTRS1988

Reactions of atomic oxygen (O/3P/) with various polymer films

An attempt is made to obtain the etch rates for various polymer films exposed to O(3P) downstream from, and out of the glow of, the O2 plasma. These rates are compared with published values from the following sources: etching in the glow of an O2 plasma, the Space Shuttle STS-8 flight experiment, and beam experiments. The etch rate data for Kapton fit a logarithmic plot (with a positive slope) of the reaction probability versus O(3P) impact energy.

Golub, Morton A.↗
NASA NTRS1987

Reactions of Atomic Oxygen (O(3P)) with Polybutadienes and Related Polymers

Thin films of the following polymers were exposed at ambient temperature to ground-state oxygen atoms (O(3P)), generated by a radio-frequency glow discharge in O2: cis- and trans-1,4-polybutadienes (CB and TB), amorphous 1,2-polybutadiene (VB), polybutadienes with different 1,4/1,2 contents, trans polypentenamer (TP), cis and trans polyoctenamers (CO and TO), and ethylene-propylene rubber (EPM). Transmission infrared spectra of CB and TB films revealed extensive surface recession, or etching, unaccompanied by any microstructural changes within the films, demonstrating that the reactions were confined to the surface layers. Contrary to the report by Rabek, Lucki, and Ranby (1979), there was no O(3P)-induced cis-trans isomerization in CB or TB. From weight-loss measurements, etch rates for polybutadienes were found to be markedly dependent on vinyl content, decreasing by two orders of magnitude from CB (2% 1,2) to structures with 30 to 40% 1,2 double bonds, thereafter increasing by half an order of magnitude to VB (97% 1,2). Relative etch rates for EMP and the polyalkenamers were in the order: EMP is greater than CO (or TO) is greater than TP is greater than CB. The sole non-elastomer examined, TB, had an etch rate about six times that of CB, ascribable to a morphology difference. Cis/trans content had a negligible effect on the etch rate of the polyalkenamers. Mechanisms involving crosslinking through units are proposed for the unexpected protection imparted to polybutadienes by the 1,2 double bonds.

Golub, Morton A.↗
NASA NTRS1981

Thermal Rearrangements of Polybutadienes with Different Vinyl Contents

A study was made of the loss of double bonds in equibinary (1,4-1,2) polybutadiene (EB) and in polybutadienes with 30% 1,2, 70% 1,4 (FI), and 10% 1,2, 90% 1,4 (DI) double-bond content, when heated in vacuum under nonpyrolitic conditions (temperature range 220-280 C). These polymers were found to undergo second-order loss of 1,2 unsaturation with similar activation energies (E(sub a) = 34.0 +/- 3 kcal/mole), by analogy to the previously reported thermally induced loss of double bonds in 1,2-polybutadiene (VB) (E(sub a) = 33.6 +/- 3 kcal/mole). Moreover, EB and Fl exhibited also second-order loss of 1,4 unsaturation, with E(sub a) ca. 36 and 40 kcal/mole, respectively, while DI showed negligible loss of 1,4 unsaturation below 260 C, in common with cis-1,4-polybutadiene (CB) (with 2% 1,2 double bonds) examined earlier. The loss of 1,2 double bonds in the various polybutadienes with different vinyl contents is accompanied by substantial methyl production, ranging from about one methyl group formed for every 4-5 vinyl units lost in VB, to one methyl for every two vinyls lost in EB,and to almost one methyl for each vinyl lost in DI or CB. Mechanisms are proposed for the thermally induced loss of 1,2 and 1,4 unsaturation in various polybutadienes and for the accompanying methyl production.

Golub, Morton A.↗
NASA NTRS1978

Low-Temperature Chemiluminescence From cis-1,4-Polybutadiene, 1,2-Polybutadiene, and trans-Polypentenamer at Temperatures Near Ambient

The chemiluminescence emission at 25-60 C was measured from films of cis-1,4-polybutadiene, 1,2-polybutadiene, and trans-polypentenamer. The polymers were autoxidized previously in air 100 C, or allowed to react with singlet molecular oxygen in solution, and then cast into films. Values of beta(or k(sub d,((1)O2 yields (3)03)/k(sub r)((1)O2 + polymer yields products)) were determined in benzene for cis-1,4-polybutadiene and cis-1,4-polyisoprene, and for model compounds cis-3-hexene and cis-3-methyl-3-hexene by independent methods. The chemiluminescence emission from irradiated films of the polymers containing a dye sensitizer showed a complicated time dependence, and the results depended on the length of irradiation.

Nathan, Richard A.↗
NASA NTRS1978

NMR and Infrared Study of Thermal Oxidation of cis-1, 4-Polybutadiene

A study of the microstructural changes occuring in CB during thermal, uncatalyzed oxidation was carried out. Although the oxidation of CB is accompanied by extensive crosslinking with attendant insolubilization, it was found possible to follow the oxidation of solid CB directly with C-13 NMR spectroscopy. The predominant products appearing in the C-13 NMR spectra of oxidized CB are epoxides. The presence of lesser amounts of alcohols, peroxides, and carbonyl structures was adduced from complementary infrared and NMR spectra of soluble extracts obtained from the oxidized, crosslinked CB. This distribution of functional groups contrasts with that previously reported for the autooxidation of 1,4-polyisoprene. The difference was rationalized in terms of the relative stabilities of intermediate radical species involved in the autoxidation of CB and 1,4-polyisoprene.

Gemmer, Robert V.↗
NASA NTRS1978

Chemiluminescence Study of the Autoxidation of cis-1,4-Polyisoprene

The free-radical mechanism for the autoxidation of cis-1,4-polyisoprene (natural rubber or its synthetic counterpart) has been investigated extensively. An important feature of this mechanism, and indeed also of the autoxidation of hydrocarbons generally, is that it is a chain process propagated by alkyl and peroxy radicals and terminated through bimolecular reactions involving these same radicals. In the usual oxidation situation, that is, at all oxygen pressures greater than a few torr, the alkyl radicals are rapidly converted to peroxy radicals, and the termination step proceeds almost exclusively through the latter radicals. The bimolecular decay of the peroxy radicals is accompanied by a weak emission of light or chemiluminescence. Kinetic evidence is consistent with an electronically excited ketone produced in the termination reaction as the source of the emission. The first observation of chemiluminescence from the oxidative degradation of polymers was reported by Ashby, who dealt mainly with polypropylene but made passing mention of several other polymers. Subsequently, a number of papers have appeared dealing with oxidative chemiluminescence from a variety of polymers. In this paper we report the first detailed study of the chemiluminescence emitted in the autoxidation of cis-1,4-polyisoprene. The chemiluminescence technique is extremely sensitive and can follow rates of oxidation that are too slow to be measured conveniently by other means. This work thus offered the potential of throwing new light on the autoxidation of cis-1,4-polyisoprene, especially in the very early stages or under ambient conditions where conventional spectroscopic procedures are rather insensitive.

Mendenhall, G. David↗