Prediction of Structures, Properties, and Functions of Alternating Copolymers of Ethylene Imine and Ethylene Oxide As an Example of Molecular Design for Polymers

Abstract

Conformational analysis of two alternating copolymers, poly(ethylene imine-alt-ethylene oxide) (PEIEO) and poly(N-methylethylene imine-alt-ethylene oxide) (PMEIEO), has been carried out by the inversionalrotational isomeric state (IRIS) analysis of ab initio molecular orbital (MO) calculations and 1 H and 13 C NMR experiments for their model compounds. On the basis of the conformational energies derived therefrom and molecular mechanics and MO calculations, higher-order structures, physical properties, and functions of the two copolymers have been predicted as an example of molecular design. These copolymers are expected to form various hydrogen bonds: PEIEO, N-H‚‚‚O (interaction energy, -1.75 kcal mol -1 ), C-H‚‚‚N (-0.68 kcal mol -1 ), and C-H‚‚‚O (-0.21 kcal mol -1 ); PMEIEO, C-H‚‚‚N (-0.66 kcal mol -1 ), and C-H‚‚‚O (-0.41 kcal mol -1 ). In particular, the N-H‚‚‚O hydrogen bond of PEIEO is too strong to be broken even by protic solvents such as methanol and water but replaced by an intermolecular N-H‚‚‚OdS attraction in dimethyl sulfoxide. The C-N and C-O bonds of PEIEO prefer the trans state as found for poly(ethylene imine) (PEI) and poly-(ethylene oxide), whereas the C-C bond does not have its own conformational preference and its conformational equilibrium is determined only by the hydrogen bond strength (HBS). The characteristic ratio of PEIEO largely depends on HBS: 1.5 (HBS ) 100%); 6.5 (0%). In contrast, the weak hydrogen bonds of PMEIEO little affect the characteristic ratio; 5.2 (HBS ) 100%); 5.9 (0%). According to Mattice's analysis (Macromolecules 2004, 37, 4711), PEIEO and PEI tend to form circular paths due to the intramolecular hydrogen bonds. Both molecular mechanics calculations using the Amber force field and density functional MO calculations under the periodic boundary condition have suggested that a double-helical structure may be formed in the PEIEO crystal. The possibility that these copolymers will be utilized as gene carriers and ion conductors is discussed, and the synthetic method is also suggested. In conclusion, these copolymers should be promising and deserve to be synthesized.

Computational design of polymers: poly(ester amide) and polyurethane

“…In a previous study, 28 we carried out conformational analysis of N-(2-methoxyethyl)methylamine (CH 3 OCH 2 CH 2 NHCH 3 ). Its most stable conformer is the tgt form with an intramolecular N-H/O attraction.…”

Predictive elucidation of conformational characteristics and configurational properties of poly(1-methylphosphirane) and poly(1-phenylphosphirane) as a molecular design

“…Solvent effects on conformations of chain molecules with heteroatoms such as nitrogen and oxygen are mainly due to selective interactions of solvents with N-H and O sites of the solutes; therefore, the solvents strongly disturb weak intramolecular attractions (e.g., N-HÁ Á ÁN, N-HÁ Á ÁO, and (C-H)Á Á ÁO) of the solutes. 2,5,13,14,17 Such solvent effects are much more influential than those due to medium permittivity. As shown here, the phosphines can hardly form attractive interactions with hard acids (e.g., hydrogen), thus being free from strong solvent a For the definitions, see Fig.…”

“…In a series of studies, we have also aimed to relate the structures and properties of the above polymers to the periodic table, i.e., electronic structures of the heteroatoms and, furthermore, to develop a methodology for molecular design of polymers. 12,17,18 By way of example of the molecular design, this study was conducted on polymers including trivalent phosphorus in the backbone, that is polyphosphines. Polyphosphines have been prepared by reduction of poly(phosphine oxide)s obtained from cationic ring-opening polymerization of deoxophostones.…”

Development of synthetic double helical polymers and oligomers

“…Besides PMMAs, poly(ethylene imine)42 and an alternating copolymer of ethylene imine and ethylene oxide43 were also reported to form a double helix in the solid state as postulated by XRD analyses.…”