Dipole Moment and Conformational Analysis of Itaconate Polymers

The dipole moments (μ) of poly(monobenzyl itaconate) (PMBzI), and of poly(dibenzyl itaconate)(PDBzI), of known tacticity (w_m), have been determined in dioxane at 25 °C: μ = 1.96 D, w_m=0.50 (PMBzI); and μ = 1.52 D,w_m= 0.25 (PDBzI). The dipole momentand the unperturbed dimensions (characteristic ratio, Cα) of polyitaconate chains are calculated theoretically, as a function ofpolymer tacticity, by matrix multiplication methods. A two-state scheme (t, g⁺) is used, with backbone bond angles close to each other.The Cα calculated increases with wm from 15.7 (syndiotactic)to 23.0 (isotactic). These high values reflect the preference for the tt conformation, andthe increase with wm shows that the preference is higher for the meso diads. Although thecomparison withthe experimental Cα's shows good agreement with those calculated, the tacticity is not enough to explain the differences between PMBzI and PDBzI, and it must be admitted that the tt conformation is favored to a greater degree in PMBzI than in PDBzI. 2,2-Dimethylsuccinate is used as model compound to obtain the modulus and orientation of the dipole moment of the repeat unit. The polymer μ calculated is scarcely sensitive to tacticity. Comparison with experimental μ shows excellent agreement in the case of PDBzI. For PMBzI, the experimental μ ishigher than calculated, and agreement requires modification of the conformational parameters (but within the precision limits of the calculation).