Molecular orbital study of the Q–e scheme in free radical copolymerization

✍ Scribed by Colthup, Norman B.

• Publisher: John Wiley and Sons
• Year: 1982
• Weight: 706 KB
• Volume: 20
• Category: Article
• ISSN: 0360-6376
• DOI: 10.1002/pol.1982.170201112

✦ Synopsis

Abstract

Molecular orbital calculations were used to study free radical polymerization. Calculations show that the monomer is activated during the reaction and the pi bond becomes a diradical. The radical on the carbon that is about to form the new bond is called the e radical in this article. The other is the Q radical. For different monomers it is shown indirectly that changes in the energies of formation of the Q and e radicals are related to changes in the Q and e terms in the empirical Q–e scheme of Alfrey and Price. The polar effect in the Q–e scheme involves the e‐radical, unpaired electron density. Specifically, the Q–e sum (e~x~ + e~y~) is correlated with the e radical spin density. Also the e term is correlated with the electron density on the unsubstituted carbon of the monomer. The relationship of the Q radical to the adjacent substituent is shown by correlating ln Q values with the energy of addition of a hydrogen atom to a monomer. These relationships give theoretical meaning to the Q–e terms and allow calculation of Q and e values from molecular orbital properties for small monomers.