Conformational characteristics of poly(ethylene sulfide) (PES), poly(ethylene oxide) (PEO), and their oligomeric model compounds have been investigated by the rotational isomeric state (RIS) analysis of ab initio molecular orbital (MO) calculations, NMR vicinal coupling constants, characteristic ratios, and dipole moment ratios. Conformational energies of PES were determined from 1H and 13C NMR vicinal constants of its monomeric model compound, 1,2-bis(methylthio)ethane (BMTE), and ab initio MO calculations for BMTE at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) and MP2/6-311+G(3df,2p)//HF/6-31G(d) levels. By the NMR analysis, the firs-order interaction energies for the gauche states around the C−C and C−S bonds, designated as Eσ and Eρ respectively, were evaluated as follows:  in benzene, Eσ = 0.41 kcal mol-1 and Eρ = −0.74 kcal mol-1; in chloroform, Eσ = 0.31 kcal mol-1 and Eρ = −0.41 kcal mol-1. The C−C and C−S bonds were shown to prefer the trans and gauche conformations, respectively. These tendencies ...

Conformational Characteristics of Poly(ethylene sulfide) and Poly(ethylene oxide): Solvent Dependence of Attractive and Repulsive Gauche Effects

Conformational characteristics of poly(ethylene imine) (PEI) have been investigated by a rotational isomeric state (RIS) analysis of ab initio molecular orbital (MO) calculations and 1H and 13C NMR experiments for a monomeric model compound, N,N‘-dimethylethylenediamine (di-MEDA). From the MO and NMR data, it was shown that the C−C and C−N bonds of di-MEDA have high gauche (71−93%) and trans (64−86%) preferences, respectively. Conformational energies of PEI were determined from the MO calculations for di-MEDA at the MP2/6-311++G(3df, 3pd)//HF/6-31G(d) level. The high gauche stability in the C−C bond was indicated to stem from a moderate and a weak intramolecular N−H···N hydrogen bonds; the interaction energies were evaluated as −1.54 and −0.58 kcal mol-1, respectively. The RIS scheme including rotational and inversional isomerizations was developed and applied to PEI to evaluate the chain dimension and diad probabilities. With the conformational energies determined as above, the characteristic ratio and m...

Conformational Analysis of Poly(ethylene imine) and Its Model Compounds: Rotational and Inversional Isomerizations and Intramolecular and Intermolecular Hydrogen Bonds

Conformational characteristics of poly(propylene sulfide) (PPS, [CH2C*H(CH3)S]x) have been investigated. Proton and carbon-13 NMR vicinal coupling constants observed from its monomeric model compound, 1,2-bis(methylthio)propane (BMTP, CH3S−CH2−C*H(CH3)−SCH3), were analyzed to yield bond conformations of the S−C, C−C*, and C*−S bonds. Ab initio molecular orbital (MO) calculations at the MP2/6-311+G(3df,2p)//HF/6-31G(d) and B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) levels were carried out for BMTP to evaluate free energies and dipole moments of all the possible conformers. Conformational energies and bond dipole moments of BMTP were estimated therefrom. Conformational energies of BMTP and PPS were also determined by simulations based on the rotational isomeric state scheme for experimental observations of bond conformations of BMTP, characteristic ratio of atactic PPS, and dipole moment ratios of isotactic and atactic PPS. The first-order interaction energies for the S−C (Eσ) and the C−C* (Eα and Eβ) bonds were...

Conformational Analysis of Poly(propylene sulfide)

Conformational characteristics of poly(tetramethylene oxide) (PTMO) have been investigated on the basis of the conformational energies evaluated for its monomer model 1,4-dimethoxybutane (DMB) from the ab initio molecular orbital (MO) calculations at the second-order Moller−Plesset correlation level with the 6-31+G* basis set. The reliability of our conformational energies was examined by comparison between calculations and observations of NMR vicinal 13C−1H and 1H−1H coupling constants of DMB and the characteristic ratio and dipole moment ratio of PTMO. Then the C−O bond dipole moment (mC-O) for the rotational isomeric state analysis of polyethers was determined from the MO and 1H NMR data reported previously for 1,2-dimethoxypropane, a monomeric model compound of poly(propylene oxide). The optimal mC-O value was obtained as 1.18 D. The conformational energies reproduced the experimental observations very well. The relationship between the conformational characteristics and crystal structures of polyethe...

Conformational Characteristics of Poly(tetramethylene oxide)

The polyoxyethylene chain—on the origin of its conformational flexibility

Third-order interactions imposed by a pair of atoms separated by five bonds are taken into account in computations of the mean-square end-to-end distance and the mean-square radius of gyration for linear polymer chains. The statistical weight matrices are established on the basis of the rotational isomeric state model. The conformational energy of n-hexane is calculated as a function of the CC bond rotation angles. The third-order interaction energy is obtained by comparison with that of n-pentane. The characteristic ratio of polymethylene is 6.6 in the third-order interaction approximation, which is in agreement with experimental data.

Xubing Song

Papers

Third‐order interaction approximation for linear polymer chains