Abstract
Molecular mechanics has been applied to model compounds of syndiotactic poly(methyl methacrylate) (PMMA). The results for the energy minimum correspond with the conformation derived in literature from wide-angle X-ray scattering. Barriers to rotation calculated for the ester and the main-chain methyl groups correspond well with available experimental data. The barrier to rotation obtained for the alkoxy group is much higher than usually expected, but the two-well potential model rules this rotation out as the molecular process responsible for the β-maximum of PMMA. The barrier to rotation obtained for the alkoxycarbonyl group is much too low to correspond to the β-maximum. Constraint of the main-chain torsion angles brings the barrier near to the activation energy of this process. We conclude that about half the experimental barrier can be attributed to matrix effects.
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