摘要: A full-relaxation optimization of molecule and the Dreiding force field are employed toobtain the geometry parameters and the conformational energy surfaces of meso or racemicdyad of poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA). Three differentcarbonyl-bond orientations of side-groups resulted in the differences in depth of potentialwells in their energetic contours for a meso or a racemic dyad. These discrepancies areinterpreted as a result of various fine structures corresponding to grid search conformations as the as thereby different interactions.The analysis on the most stable conformations of PMAA confirmed that the ester groups are nearly perpendicular to the plane defined by the two adjacent skeletal bonds but may possibly change their relative orientations to meet the requirement of lower energy during the conformational state transition.For each polymer,two global energy maps of a meso and a racemic dyad were finally constructed from the superposition of energy data for the three kinds of side-group orientations by the Boltzmann factors.From an ensemble average,the proposed scheme with three rotational isomeric states(RIS) allowed us to access the experimentally unperturbed dimensions of PAA chain via the configurational statistical mechanics.Although the calculation was based on the short-range,local interactions,it was interested to note that the experimental characteristic ratios just fell within the range calculated for atactic chains.