THE RADIATION INDUCED cis-trans ISOMERIZATION OF POLYBUTADIENE. PART III
A study was made of the gamma -ray induced cis-trans isomerization of polybutadiene in solution and in the solid state in the absence of any deliberately added sensitizer. Starting with an essentially all-cis or all-trans polybutadiene, the unsensitized isomerization approached a radiostationary equilibrium in which the cis/trans ratio in the polymer was about 20/80, in contrast to the thermodynamic equilibrium ratio of 8/92 obtained in previous sensitized isomerizations of polybutadiene. The unsensitized reaction was first order in cis (or trans) content with a rate that was proportional to the radiation inteasity. The isomerization in a 1% solution in benzene was about eight times as fast as that in the pure polymer. The G/sub 0/ values for the cis yields trans reaction (i.e., the number of cis double bonds initially convented to trans per l00 ev of energy absorbed by the polymer and the solvent in the solution case and by the polymer alone in the solid state case) are about l.2 and l4.6, respectively. The corresponding G/sub 0/ values for the trans yields cis reaction are about 0.3 and 3.6, respectively. The mechanism of the unsensitized isomerization is believed to involve excitation of the pi electrons of the polymer double bonds to an antibonding state where free rotation, and hence geometric interconversion, can occur. This excitation in the solid state presumably results from collisions of energetic electrons with the polymer molecules. The double bond electrons are excited directly ard/or indirectly through intramolecular energy transfer from the methylenic groups in the polymer. These processes occur also in solution but are less important there than intermolecular energy transfer from excited or ionized solvent molecules to the polymer double bonds. (auth)
- Research Organization:
- B.F. Goodrich Co. Research Center, Brecksville, Ohio
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-15-000243
- OSTI ID:
- 4130060
- Journal Information:
- Journal of the American Chemical Society (U.S.), Journal Name: Journal of the American Chemical Society (U.S.) Vol. Vol: 82; ISSN JACSA
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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