An approximate analytical solution is presented for the rotational isomeric state model of flexible polymer configurations. lgr;max, the largest eigenvalue of the generating matrix, is obtained as a perturbation expansion in powers of sgr;/lgr;1, where lgr;1is the largest eigenvalue of the statistical matrix and sgr;=exp(minus;Eg/kT), whereEgis thegaucheenergy relative to thetrans. The method results in a characteristic polynomial for which lgr;maxis the largest root. For the cubic polynomial the results differ from the exact results, obtained by diagonalizing the generating matrix, by 0.5ndash;5percnt; depending on sgr;/lgr;1. The method was applied to calculate lang;r2nrang; and lang;D200(OHgr;n) rang;.
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