CALCULATION OF BARRIERS TO ROTATION IN PEEK AND SOME OF ITS SUBSTITUTED DERIVATIVES

Barriers to rotation have been calculated by molecular mechanics, usin g the force field MM+, for a fragment of PEEK and its methyl, ethyl, i sopropyl, tert-butyl and di-tert-butyl, substituted derivatives. The b arrier for the nearer C-O bond increases from 2.0 kcal/mol in KEEK to 16 kcal/mol in dibutyl substituted KEEK as the bulkiness of the substi tuent increases. The rotation barrier of the further C-O bond is not a ffected by the substituent.