CONFORMATIONAL CHARACTERISTICS OF POLY[OXY(1-ALKYLETHYLENES)] CARRYING SIDE-CHAINS SUCH AS ETHYL, ISOPROPYL, AND TERT-BUTYL GROUPS

Configuration-dependent properties of a series of poly[oxy(l-alkylethylene)] chains CH3O- [-CH2CH(R)0-]xCH3 having various side chains differing in size and shape were examined. Conformational energy parameters established for poly(oxypropylene) in the preceding paper were adopted in common to the skeletal configuration, steric interactions imposed by larger substituents being taken into account separately. Within the reasonable range of conformational energies, observed values of the characteristic ratio (μ2)0/nP (R = CH2CH3, C(CH3)3) and the dipole moment ratio (μ2)/nm2 (R = CH(CH3)2) for isotactic polymers were reproduced. Fractions of the conformation about internal C-C bonds calculated by using the same parameter set were compared favorably with those estimated from NMR data (R = CH(CH3)2, C(CH3)3). Calculations were extended to evaluate (μ2)0/nl2 and (u2)/nm2 for atactic to syndiotactic chains. In the case of poly- [oxy(l-tert-butylethylene)], values of (μ2)0/nl2 decrease drastically from 16.0 for the isotactic to 0.9 for the syndiotactic chain. The latter value is smaller than that (2.2) calculated for the freely rotating model, indicating that the polymer chain configuration is remarkably compact in the state unperturbed by any long-range interactions. Finally, the partition function z for a monomer residue were deduced from the corresponding molecular partition function Z by Z = zx. The conformational flexibility of the isotactic chain thus estimated decreases in the order R = (z = 4.35) > CH2CH3 (3.96) > CH3 (3.65) ≫ CH(CH3)2 (2.15) ≫ C(CH3)3 (1.42). Characteristics associated with the cooperative nature of bond rotations along the polymer chain are discussed in comparison with those of vinyl polymers. © 1979, American Chemical Society. All rights reserved.