Conformational characteristics of poly(3-hydroxyvalerate) (P3HV) and structure-property relationships of P3HV and poly(3-hydroxybutyrate).

Conformational analysis of biosynthetic and biodegradable poly(3-hydroxyvalerate) (P3HV), an analog of poly(3-hydroxybutyrate) (P3HB), was performed. The only structural difference between the two polymers consists in the side chain, which is either methyl (P3HB) or ethyl (P3HV). Molecular orbital calculations and NMR experiments were conducted on a monomeric model compound to determine the bond conformations of the main and side chains of P3HV. The refined rotational isomeric state (RIS) scheme was applied to derive configurational properties of P3HV. The characteristic ratio of P3HV (2.1-3.0) is smaller than that of P3HB (5.4-5.6), indicating greater conformational flexibility of the P3HV chain. The increased flexibility due to the internal rotation of the ethyl side group of P3HV results in a lower equilibrium melting point (130 °C) compared with P3HB (203 °C). The RIS calculations on P3HV also suggested its potential for rubber-like properties. Periodic density functional theory calculations were used to optimize the crystal structures of P3HB and P3HV and obtain their elastic moduli. Three-dimensional Young's modulus distributions of both crystals are closer to isotropic than anisotropic. In conclusion, the material design and usage of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) are discussed.

Conformational characteristics and conformation-dependent properties of poly(ε-caprolactone).

Structures and properties of isolated and crystalline poly(ε-caprolactone) (PCL) chains have been investigated. Ab initio molecular orbital (MO) calculations were conducted for methyl 6-acetoxyhexanoate (MAH), a model compound of PCL, to yield Gibbs free energies of all its existent conformers. Bond conformations of its seven bonds corresponding to the repeating unit of PCL were calculated therefrom; two C-C bonds close to the ester group show gauche preferences owing to intramolecular C-H⋯O attractions, and the other five prefer trans forms. 1H and 13C NMR vicinal coupling constants of 13C-labeled MAH yielded bond conformations consistent with the MO calculations. The rotational isomeric state (RIS) calculations on PCL led to the characteristic ratios (4.1-4.5) that agree with those estimated experimentally from the Stockmayer-Fixman plots. Periodic density functional theory calculations on PCL crystals yielded the optimum structures and Young's moduli in the a-, b-, and c (fiber)-axis directions. The fiber-axis modulus (252 GPa) falls short of that (333 GPa) of polyethylene but exceeds that (182 GPa) of poly(ethylene terephthalate), whereas the three-dimensionally averaged Young's modulus (10.7 GPa) of PCL is the smallest of those of representative polymers investigated so far. The enzymatic selectivity of biodegradable polyesters is discussed herein in terms of their conformational characteristics and surface structures of enzymes.

Molecular Design of Aromatic Polythionoesters.

As an example of molecular design of new polymers, structures and properties of poly(ethylene thionoterephthalate) (PET[S2]) and the related polymers have been predicted from calculations of ab initio molecular orbital (MO) theory, rotational isomeric state (RIS) scheme, and periodic density functional theory (DFT). The MO calculations were confirmed by NMR experiments and introduced to the RIS scheme for PET[S2] to yield its configurational properties, which are compared herein with those of analogous polyester, polythioester, and polydithioester. Configurational properties of randomly thiono-substituted poly(ethylene terephthalate) (PET), PET[S z O1-z ], were also evaluated as a function of sulfidity (z). On the assumption that the crystal of PET[S2] can be expressed as an isomorphic replacement of the PET crystal, the crystal structure was optimized by a periodic DFT simulation and its Young's moduli in the a-, b-, and c-axis directions were, respectively, evaluated to be Ea = 0.94(7.20) GPa, E b = 19.58(22.26) GPa, and E c = 142.1(182.4) GPa, where the parenthetic values are those of the PET crystal. There is a possibility that properties of PET[S z O1-z ] will be controlled between those of PET and PET[S2] by adjusting the sulfidity. The potential practical applications of the polythionoesters are also discussed herein. By purely theoretical computations, the structures and properties of the not-yet synthesized polymers were predicted quantitatively; that is, the theoretical molecular design of new polymers has been achieved.

Crystal structure of butane-1,4-diyl bis-(furan-2-carboxyl-ate).

The asymmetric unit of the title compound, C14H14O6, a monomeric compound of poly(butyl-ene 2,5-furandi-carboxyl-ate), consists of one half-mol-ecule, the whole all-trans mol-ecule being generated by an inversion centre. In the crystal, the mol-ecules are inter-connected via C-H⋯O inter-actions, forming a mol-ecular sheet parallel to (10). The mol-ecular sheets are further linked by C-H⋯π inter-actions.

Crystalline Moduli of Polymers, Evaluated from Density Functional Theory Calculations under Periodic Boundary Conditions.

A theoretical methodology based on quantum chemistry to calculate mechanical properties of polymer crystals has been developed and applied to representative polymers. By density functional theory calculations including a dispersion force correction under three-dimensional periodic boundary conditions, crystal structures of poly(methylene oxide) (PMO), polyethylene (PE), poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT), and poly(butylene terephthalate) (PBT) were optimized and their mechanical properties, such as crystalline moduli and linear and volume compressibilities, were calculated. The optimized crystal structures were proved to be fully consistent with those determined by X-ray and neutron diffraction. The crystalline moduli (E ∥) parallel to the chain axis were calculated to be 114 GPa (PMO), 333 GPa (PE), 182 GPa (PET), 7.1 GPa (PTT), and 20.8 GPa (PBT) and compared with those determined from X-ray diffraction, Raman spectroscopy, and neutron inelastic scattering experiments. Herein, the E ∥ values thus determined are interpreted in terms of conformational characteristics of the polymeric chains and the validity of the homogeneous stress hypothesis adopted in the X-ray diffraction method is also discussed.

Computational Characterization of Nylon 4, a Biobased and Biodegradable Polyamide Superior to Nylon 6.

This study is an attempt to develop a theoretical methodology to elucidate or predict the structural characteristics and the physical properties of an isolated polymeric chain and its crystalline state precisely and quantitatively. To be more specific, conformational characteristics of a biobased and biodegradable polyamide, nylon 4, in the free state have been revealed by not only ab initio molecular orbital calculations on its model compound but also nuclear magnetic resonance experiments for the model and nylon 4. Furthermore, the crystal structure and solid-state properties of nylon 4 have been elucidated by density functional theory calculations with a dispersion force correction under periodic boundary conditions. In the free state, the nylon 4 chain forms intramolecular N-H···O=C hydrogen bonds, which force the polymeric chain into distorted conformations including a number of gauche bonds, whereas nylon 4 crystallizes in the fully extended all-trans structure (α form) that is stabilized by intermolecular N-H···O=C hydrogen bonds. The intermolecular interaction energy (ΔE CP) in the crystal was accurately calculated via a counterpoise (CP) method contrived here to correct the basis set superposition error, and the ultimate crystalline modulus (E b ) in the chain axis (b axis) direction at 0 K was also evaluated theoretically. The results were compared with those obtained from the α and γ crystalline forms of nylon 6, and, consequently, the superiority of nylon 4 to nylon 6 in thermal stability and mechanical properties was indicated: the ΔE CP and E b values are, respectively, -214 cal g-1 and 334 GPa (nylon 4), -191 cal g-1 and 316 GPa (α form of nylon 6), and -184 cal g-1 and 120 GPa (γ form of nylon 6). In conclusion, nylon 4 is expected to be put to practical use as a tough environmentally friendly polyamide.

Crystal structures of 2-(benzene-carbo-thio-yloxy)ethyl benzene-carbo-thio-ate and 2-(benzene-carbo-thio-yloxy)ethyl benzoate.

The title compounds, C16H14O2S2 and C16H14O3S, which are monomeric models (models D and E) for a polythio-noester and a poly(ester-co-thio-noester), respectively, crystallize in the space group P21/c and are isostructural with each other. The mol-ecule in each crystal is located on an inversion centre and has an all-trans structure. The asymmetric unit comprises one half-mol-ecule. In the crystal, there are inter-molecular C⋯S contacts [3.391 (3) and 3.308 (3) Šfor models D and E, respectively] and C-H⋯π inter-actions, which form a layer structure parallel to the bc plane. The carbonyl and thio-carbonyl groups of the model E compound are each disordered over two equivalent sites about the inversion centre with equal occupancies.

Structure-Property Relationships of Poly(ethylene carbonate) and Poly(propylene carbonate).

Conformational characteristics of poly(ethylene carbonate) (PEC) and poly(propylene carbonate) (PPC) have been revealed via molecular orbital (MO) calculations and nuclear magnetic resonance (NMR) experiments on model compounds with the same bond sequences as those of the polycarbonates. Bond conformations derived from the MO calculations on the models were in exact agreement with those from the NMR experiments. Both PEC and PPC were indicated to adopt distorted conformations including a number of gauche bonds and cover themselves with negative charges, thus failing to form a regular packing and remaining amorphous. The MO data were applied to the refined rotational isomeric state (RIS) calculations to yield configurational properties such as the characteristic ratio, its temperature coefficient, the configurational entropy, and average geometrical parameters of unperturbed PEC and PPC chains. In the RIS calculations on PPC, the regio- and stereosequences were generated according to the Bernoulli trial or Markov stochastic process. In consequence, it was shown that the configurational properties of PPC do not depend significantly on its regio- and stereoregularities. The internal energy contribution to rubberlike chain elasticity, calculated from the temperature coefficient of the characteristic ratio, has indicated the possibility that PEC and PPC will behave as elastomers. The practical applications and potential utilizations of the polycarbonates are discussed on the basis of the conformational characteristics and configurational properties.

N,N'-(Propane-1,3-di-yl)dibenzo-thio-amide.

The title compound, C17H18N2S2, exhibits a trans-trans-trans-gauche(+) (tttg (+)) conformation with regard to the NH-CH2-CH2-CH2-NH bond sequence. In the crystal, mol-ecules are connected by N-H⋯S=C and C-H⋯S=C hydrogen bonds, forming a herringbone arrangement along the c-axis direction. The two thioamide groups make dihedral angles of 43.0 (2) and 33.1 (2)° with the adjacent phenyl rings.

N,N'-(Ethane-1,2-di-yl)di-benzene-carbo-thio-amide.

The title compound, C16H16N2S2, adopts a gauche (+)-gauche (+)-gauche (+) (g(+)g(+)g(+) ) conformation in the NH-CH2-CH2-NH bond sequence. In the crystal, mol-ecules are connected by pairs of N-H⋯S=C hydrogen bonds and C-H⋯π inter-actions, forming a tape structure along the c-axis direction.

S,S'-Butane-1,4-diyl bis-(benzene-carbo-thio-ate).

The title compound, C18H18O2S2, which lies on an inversion center, adopts a gauche (+)-trans-trans-trans-gauche (-) (g (+) tttg (-)) conformation in the S-CH2-CH2-CH2-CH2-S bond sequence. In the crystal, mol-ecules are packed in a herringbone arrangement through inter-molecular C-H⋯π inter-actions.

Butane-1,4-diyl bis-(benzene-carbodi-thio-ate).

The title compound, C18H18S4, which lies on an inversion center, adopts a trans-gauche (+)-trans-gauche (-)-trans (tg (+) tg (-) t) conformation of the S-CH2-CH2-CH2-CH2-S bond sequence. In the crystal, a π-π inter-action with a centroid-centroid distance of 3.8797 (16) Šis observed.

Ethane-1,2-diyl bis-(benzene-dithio-ate).

In the crystal structure, the title compound, C(16)H(14)S(4), is located on an inversion center and exhibits a gauche(+)-trans-gauche(-) conformation in the S-CH(2)-CH(2)-S bond sequence. The S-C=S plane makes a dihedral angle of 30.63 (17)° with the phenyl ring. An inter-molecular C-H⋯π inter-action is observed.

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

Conformational characteristics and configurational properties of poly(1-methylphosphirane) (PMePP) and poly(1-phenylphosphirane) (PPhPP) have been predictively elucidated by the refined rotational isomeric state scheme coupled with ab initio molecular orbital and density functional calculations. The lone pair of the phosphorus atom adopts an sp hybrid orbital. Owing to the high s character (50%), the polyphosphiranes exhibit low proton (hydrogen) affinities, and hence the lone pair does not form any intramolecular attractive interactions with hydrogen. As the meso-diad probability varies from 0 (syndiotactic) to 1 (isotactic), the characteristic ratio of PMePP slightly increases from 6.7 to 7.4, whereas that of PPhPP considerably decreases from 38 to 7.3. The large dimension of syndiotactic PPhPP is chiefly due to π-π attractions formed between adjacent phenyl groups. The trivalent phosphorus atom may be bonded to heavy, noble, and transition metals but readily or gradually oxidized. The usefulness and necessity of the polyphosphiranes have been assessed.

Structure-property relationships of polyselenoethers [-(CH2)ySe-]x (y=1, 2, and 3) and related polyethers and polysulfides.

Conformational characteristics, solution (melt) properties, and thermal properties of polyselenoethers [-(CH2)ySe-]x ( y=1, 2, and 3) have been revealed by the rotational isomeric state analysis of ab initio molecular orbital calculations and (1)H and (13)C NMR experiments for monomeric model compounds and compared with those of typical polyethers and polysulfides. The comparative results are summarized here as correlations in conformation among model compounds and unperturbed and crystalline states of the polymers, and thermal properties of the polymer crystals are discussed in terms of intramolecular and intermolecular interactions. By ab initio molecular orbital calculations under periodic boundary conditions, helical structures of poly(methylene oxide), poly(methylene sulfide), and poly(methylene selenide), and the crystal structure of poly(ethylene selenide) have been optimized, and their electronic structures have been predicted. A systematic methodology to predict and characterize up to higher-order structures and various physical properties of polymers incorporated in different phases has been attempted to be developed.

Conformational peculiarities of alcohols incorporated in lyotropic and thermotropic liquid crystals.

Conformational characteristics of 1-butanol incorporated not only in hexagonal and lamellar aggregates formed by a lyotropic liquid crystal composed of sodium octanoate, 1-butanol, and water but also in a thermotropic liquid crystal, 4'-methoxybenzylidene-4-n-butylaniline (MBBA), have been investigated from 2H NMR quadrupolar splittings of the perdeuterated and partially deuterated compounds. In the lyotropic phases, 1-butanol shows strong trans preferences and renders itself extended, and octanoate decreases the trans fraction toward the methyl terminal to fill the inner space of the aggregate on behalf of 1-butanol. In MBBA, 1-butanol prefers globular conformations. This tendency was also indicated from the phase behaviors of 1-butanol/MBBA and 1-decanol/MBBA systems. In the nematic field, two successive C-C bonds of 1-butanol mostly adopt g+/-g+/- conformations, which are formed in the vicinity of the headgroup of 1-decanol in the lamella of the sodium octanoate/1-decanol/water system. A large degree ofconformational freedom near the hydroxyl group of alcohols, being shown by ab initio molecular orbital calculations at the Gaussian-2 level, permits them to change conformation for each environment.