Masamichi Kobayashi

THEORETICAL EVALUATION OF THREE-DIMENSIONAL ELASTIC CONSTANTS OF NATIVE AND REGENERATED CELLULOSES : ROLE OF HYDROGEN BONDS

Three-dimensional elastic constants were calculated for cellulose crystalline forms I and II (native and regenerated celluloses, respectively). The calculated Youngs modulus El along the chain axis is 167.5 GPa for form I and 162.1 GPa for form II. The El of form II has only a slightly lower value than that for form I. This is consistent with the X-ray data (c. 120–140 GPa for form I and c. 110 GPa for form II) although the absolute values are large. The El was found not to be affected by intermolecular interactions but by intramolecular hydrogen bonds along the chain axis, especially the bond between the hydroxyl side group and the ether oxygen atom of the glucose ring (type a). A calculation neglecting this hydrogen bond gives the largely reduced El of c. 70 GPa. Anisotropy of the Youngs modulus and linear compressibility in the planes perpendicular to the molecular chain axis were also calculated. In the form I crystal, where the hydrogen-bonded sheet planes are stacked together by non-bonded van der Waals interactions, the modulus is large within the sheet plane and small in the direction perpendicular to the sheet: the anisotropy is similar to that reported for the nylon 6 α and γ forms. In form II the modulus is large but the anisotropy is not so remarkable, which is similar to atactic poly(vinyl alcohol) and poly(m-phenylene isophthalamide). The same tendency is seen also for the linear compressibility. In parallel with the calculation of the elastic constants, the lattice vibrational frequencies were calculated for forms I and II and compared with the observed infra-red and Raman spectral data so as to confirm whether the force fields used were reasonable.

Structural study on ferroelectric phase transition of vinylidene fluoride-trifluoroethylene copolymers (III) dependence of transitional behavior on VDF molar content

Abstract Structural changes occurring in the ferroelectric phase transition of vinylidene fluoride-trifluoroethylene (VDF-TrFE) copolymers with the various VDF molar contents have been investigated by means of X-ray diffraction and infrared spectroscopic methods. The phase transition occurs among three crystal phases of the low-temperature (regular all-trans conformation), the high-temperature (gauche conformation with a large rotational motion), and the cooled phases (disordered trans conformation). In the copolymer with low VDF molar content less than 40%, the broad transition between the cooled phase and the high-temperature phase is observed and the conformational change from trans to gauche is not so perfect. In the range of VDF 50–60%, the transition becomes more definite, and on the way of heating the low-temperature phase transforms to the cooled phase, which transfers continuously to the high-temperature phase. For copolymers of VDF 70–80%, a clear and discontinuous first order transition between...

Normal Vibrations of the Polymer Molecules of Helical Conformation. V. Isotactic Polypropylene and Its Deuteroderivatives

Polarized infrared spectra of isotactic polypropylene (IPP), [Complex chemical formula] were measured in the region from 4000 to 80 cm−1. The normal vibrations of these three polymers were calculated for the infrared‐ and Raman‐active A and E species, by the use of the GF‐matrix method with the Urey—Bradley force field. The results show a fairly good agreement between the observed and calculated frequencies. The assignments of the absorption bands were given, and discussions were made on the vibrational modes of the bands characteristic of the isotactic helical structures. A computation program for calculating the characteristic values and vectors of a Hermitian matrix was presented.From the normal coordinate treatment applied to the threo‐ and erythro‐ model of di‐isotactic polypropylene‐1‐d, [Complex chemical formula] it was found that the polymers prepared from trans‐ and cis‐propylene‐1‐d, CHD, CH–CH3, have threo‐ and erythro‐di‐isotactic structures, respectively, suggesting cis‐opening mechanism in t...

Structural phase transition in ferroelectric fluorine polymers: X-ray diffraction and infrared/Raman spectroscopic study

Abstract The structural phase transition has been investigated by X-ray diffraction and infrared and Raman spectroscopic measurements for ferroelectric fluorine polymers, including poly(vinylidene fluoride) and its copolymers with trifluoroethylene or tetrafluoroethylene. One of the most characteristic features of this ferroelectric transition is the large conformational change of the molecular chains between the trans and gauche rotational isomers, quite different from the structural change observed generally in the usual ionic ferroelectric materials. The crystallization and transition behaviors depend sensitively on the monomer composition in the copolymers as well as on the sample preparation conditions. The roles of the optic and acoustic phonons in the ferroelectric phase transition have been discussed based on the temperature dependences of the far-infrared spectra and the ultrasonic velocity.

Normal Vibrations of the Polymer Molecules of Helical Configuration. III. Polyoxymethylene and Polyoxymethylene‐d2

Polarized infrared spectra of polyoxymethylene (POM), — (CH2O)n—, and POM‐d2, — (CD2O)n— have been measured in the region from 4000 to 100 cm—1. The spectra of POM at elevated temperatures were also observed. The selection rules for POM molecules are derived under the factor group D(10π/9). The normal vibrations of POM and POM‐d2 are calculated for the Raman active A1 symmetry species, the infrared active A2 species and the Raman and infrared active E1 species, by the use of the GF‐matrix method with the Urey—Bradley force field taking into account the torsional displacement coordinates of the skeleton. The results show fairly good agreement of the observed and calculated frequencies. The assignments of the bands are given and discussed.

Crystal structural change in poly(3-alkyl thiophene)s induced by iodine doping as studied by an organized combination of X-ray diffraction, infrared/Raman spectroscopy and computer simulation techniques

Abstract Preliminary results of the structural analysis of pristine and iodine-doped poly(3-alkylthiophene)s [poly(3-hexylthiophene) and poly(3-dodecylthiophene)] have been recorded by utilizing an organized combination of X-ray imaging plate and computer simulation techniques. The crystal structure of the pristine polymers was found to be composed of stacked layers constructed by a side-by-side arrangement of alkyl groups, where both the single and double layer structures were possible. The iodine-doped poly(3-alkylthiophene)s have been found to possess a tunnel structure produced by a cooperative translation of the polymer chains along the chain axis by half the repeating period, into which polyiodide ions such as I 3 − and I 5 − were trapped to form a charge-transfer complex with polythiophene skeletal chains. These structural changes were simulated by constructing energetically minimized crystal structural models, which gave X-ray fibre diagrams close to those of the observed ones. The infrared and Raman spectra were found to change in two stages during iodine doping, and the possibility of polaron and bipolaron species constructed by a combination of polythiophene and iodine ions was proposed.

Structure and piezoelectricity of poly(vinylidene fluoride)

Abstract A theoretical equation for calculating piezoelectric constants (dij) of polymer crystals has been derived and applied to poly(vinylidene fluoride) form 1. The calculated d 33 = -2.5 × 10−11 C/N, is in good agreement with the value of -2 × 10−11 C/N measured by the x-ray method. The calculated d 31, -0.025 × 10−11 C/N, is smaller by two digits than d 33, consistent with the experimental result that the x-ray (002) spot was not shifted nearly as much by the application of the electrostatic field as in the case of d 33 The macroscopic piezoelectric constants d M 31 and d M 33 have been estimated by using a model where the piezoelectric crystal form 1 is embedded in the nonpiezoelectric amorphous matrix; d M 31 = 0.6 × 10−11 C/N and d: = -1.4 × 10−11 C/N at room temperature and d M 31 = 6.8 × 10−13 C/N and d M 33 = -0.5 × 10−11 C/N below the glass transition temperature (Tg ), respectively. These are in the same order as the values observed both at room temperature and below Tg . In the present estim...

Structure and ferroelectric phase transition of vinylidene fluoride-trifluoroethylene copolymers: 2. VDF 55% copolymer

Abstract Molecular and crystal structure changes in ferroelectric phase transition of vinylidene fluoride-trifluoroethylene (VDF-TrFE) copolymer with a VDF content of 55 mol% have been investigated by X-ray diffraction and infra-red and Raman spectroscopy. As the temperature rises from room temperature to the Curie point of ∼60°C, the polar low-temperature phase consisting of all-trans chains experiences a first-order transition to the phase of tilted long trans segments connected by some skew bonds. At higher temperature this new phase transforms continuously and steeply to the non-polar high-temperature phase, where the molecular structure consists of a random combination of TG, TḠ, T3G and T 3 G rotational sequences. In the cooling process the high-temperature phase transforms to the cooled phase, which is essentially equivalent to the phase appearing intermediately in the heating process from the low-temperature to the high-temperature phase. The cooled phase gives a tilting X-ray fibre diagram and is found by X-ray analysis to contain an appreciable amount of so-called 60° domain structure. These are well interpreted by a conformational model of tilting trans structure containing skew linkages. The tensile stress along the fibre axis causes the transformation from the cooled phase to the low-temperature phase, where the probability of 60° domain structure and the degree of chain tilting are remarkably reduced.

Morphological effect on the Raman frequency shift induced by tensile stress applied to crystalline polyoxymethylene and polyethylene: spectroscopic support for the idea of an inhomogeneous stress distribution in polymer material

A tensile-stress-induced low-frequency shift was measured for the Raman bands of crystalline polyoxymethylene (POM) and polyethylene (PE) with different draw ratios λ. The apparent frequency-shift factor p (= ΔvΔσbulk) for the 539 cm−1 skeletal bending mode δ (COC) was found to become larger for the POM sample with lower λ: p = −24 cm−1/GPa (λ = 7), −19 (λ = 17) and −11 (λ = 34). Such a difference in p was too small to detect for the skeletal stretching modes of PE samples with λ = 7 to 100: p = −6.0 cm−1/GPa for vas (CC) at 1064 cm−1 and −4.5 for vs (CC) at 1131 cm−1. This experimental fact, i.e. the dependence of the frequency-shift factor p on sample morphology, cannot be reasonably explained in terms of a homogeneous stress distribution or the simple mechanical series model of crystalline and amorphous phases. Based on the complex mechanical model (i.e. the parallel-series and series-parallel models), the Raman shift could be understood quantitatively, and the intrinsic shift factor α of the crystalline region was estimated as −11 cm−1/GPa for the δ (COC) mode of POM and as −5.0 cm−1/GPa for vas (CC) and −3.8 cm−1/GPa for vs (CC) of PE. A change in the Raman band profile under tensile stress was simulated and compared with the observed data.

Phase transition at a temperature immediately below the melting point of poly(vinylidene fluoride) from I: A proposition for the ferroelectric Curie point

Abstract A phase transition at a temperature immediately below the melting point of poly(vinylidene fluoride) form I has been found by means of differential scanning calorimetry (d.s.c.) and infra-red (i.r.) vibrational spectroscopy. An endothermic d.s.c. shoulder has been observed at a temperature about 10°C below the melting point, in the vicinity of which the i.r. crystalline trans bands decrease in intensity steeply and the crystalline gauche bands increase in intensity, indicating the conformational change from all- trans to T 3 GT 3 G type. These observations have been found to be detectable more clearly for samples subjected to the poling treatment under a d.c. high voltage. The transition shows the characteristic behaviour essentially identical to those observed for ferroelectric copolymers of vinylidene fluoride and trifluoroethylene, except for the irreversibility of the structural change, suggesting that the phase transformation revealed here may be a ferroelectric-to-paraelectric phase transition of polar form I crystal and the the Curie point may be about 172°C. It is consistent with Micherons measurement of the temperature dependence of the dielectric constant. Other structural changes in the form I sample occurring in the temperature range from 20° to 170°C have also been discussed based on the i.r. spectral measurements.