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Conformational Preferences and the Norrish II Cleavage of Polymers

IP.com Disclosure Number: IPCOM000045622D
Original Publication Date: 1983-Apr-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Jackson, WR: AUTHOR

Abstract

The degradation of ketone polymers frequently relies on the Norrish type I and/or type II photochemical reaction. This is moderately effective in cases where the ketonic group is attached to the polymer backbone (pendant group) (Fig. 1) . In this case there is only one b-hydrogen atom available to partake in the Norrish II cleavage reaction. Also, since polymer chains or portions thereof in thin films do not undergo significant confromational change during the lifetime of a ketone-excited state, a high quantum yield for the Norrish II reaction in Fig. 1 follows only if polymer I exists within a rather narrow range of conformations. However, it may be possible to utilize an observation recently reported by Reimschuessel and DeBona (Macromol 13, 1582 (1980)) to greatly enhance the degradation of a ketone polymer.

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Conformational Preferences and the Norrish II Cleavage of Polymers

The degradation of ketone polymers frequently relies on the Norrish type I and/or type II photochemical reaction. This is moderately effective in cases where the ketonic group is attached to the polymer backbone (pendant group) (Fig. 1) . In this case there is only one b-hydrogen atom available to partake in the Norrish II cleavage reaction. Also, since polymer chains or portions thereof in thin films do not undergo significant confromational change during the lifetime of a ketone-excited state, a high quantum yield for the Norrish II reaction in Fig. 1 follows only if polymer I exists within a rather narrow range of conformations. However, it may be possible to utilize an observation recently reported by Reimschuessel and DeBona (Macromol 13, 1582 (1980)) to greatly enhance the degradation of a ketone polymer. It was observed by the above authors that polyester II was characterized by an unusually high glass transition temperature (Tg=120 degrees, Tm=250degrees C) while polyester III (Fig. 2), in addition to being lower melting (Tm=185 degrees C) then the more alphatically substituted II, had a "normal" Tg. This result, along with other data, was interpreted in terms of a lower free energy of II in the glassy state due to a conformational preference. It was purposed that the intra-aromatic portion of II existed in structure IV (Fig. 3) due to the fact that the electronegatively polarized carbonyl oxygen atom can closely approach the electropositively polarized gem-dimethyl carbon atom via a relatively strainless conformation. In addition, it was suggested that in this conformation not only is the electrostatic potential minimize...