Piezoelectric properties and molecular motion of poly(β-hydroxybutyrate) films

Piezoelectric, elastic, and dielectric properties of films of poly(β-hydroxybutyrate) (PHB), an optically active natural polymer, were measured as functions of frequency and temperature. In mechanical properties, three relaxation processes were observed at 10 Hz: the α dispersion at 130°C, the β dispersion at room temperature, and the γ dispersion at ?120°C. It was concluded from x-ray diffraction and the thermal expansion coefficient that the α dispersion can be ascribed to thermal molecular motions in the crystalline phase, that the β dispersion is the primary dispersion due to the glass transition, and that the γ dispersion is related to local molecular motion of the main chains in the amorphous phase. Piezoelectric relaxations were also observed in these relaxation regions. It is proposed that the high-temperature process is due to ionic dc conduction. The piezoelectric relaxation at room temperature is ascribed to the increase of piezoelectric activity in the oriented noncrystalline phase, in which the sign of the piezoelectric modulus is opposite to that in the oriented crystalline phase.     

Piezoelectricity in oriented films of poly(γ-benzyl-L-glutamate)

Oriented films of poly(γ-benzyl L -glutamate) (PBLG) were prepared by two methods. Films of PBLG cast from chloroform solutions were elongated by rolling at 70°C. A solution of PBLG in methylene bromide was placed in a magnetic field of about 7000 gauss and the solvent was slowly evaporated for a few days until an oriented film was obtained. The real and imaginary components of the complex piezoelectric strainconstant d₂₅^* = d₂₅′ ? jd₂₅″ were determined over the temperature range from ?180°C to +180°C at a frequency of 20 Hz. The constants showed dispersions at about 20°C and about 100°C, where dynamic viscoelastic dispersions were also observed. Degree of crystallinity X_c and degree of orientation II_a of crystallites were determined from x-ray diffraction diagrams. The product X_cII_α and the value of d₂₅′ at room temperature were found to be linearly related, and both showed a maximum at an elongation ratio of 1.5 (the ratio of the final to initial length) for roll-oriented films and at an initial solution concentration of 15% by weight for magnetically oriented films. The largest values of d₂₅′ were approximately 2 × 10^?12 and 4 × 10^?12 coulomb/newton, respectively, at room temperature.     

Temperature variation of piezoelectric moduli in oriented poly(γ-methyl L-glutamate)

The real and imaginary components of the complex piezoelectric strain constant, which relates the polarization to the applied stress, have been determined for elongated films of poly(γ-methyl L -glutamate) over the temperature range ?170°C to +170°C at a frequency of 20 Hz. The variation of the piezoelectric constant with temperature is similar for both α-helical and β-form molecular conformations. The sign of piezoelectric polarization is opposite for L and D polymers. A simple model, representing the piezoelectric crystallites as embedded in nonpiezoelectric amorphous regions, is proposed to account for the piezoelectric temperature dispersion curves.     

Thermal properties of some hydrogenated poly(α-methyl styrenes)

The Synthesis of poly(isopropenyl cyclohexane) via the hydrogenation of poly(α-methyl styrene) is described. Depending on the reaction time and catalyst system a homopolymer or a copolymer is obtained. Under the conditions of synthesis both materials are highly syndiotactic. For the pure hydrogenated homopolymer (>99.9%) the glass transition temperature was found to be 185.4°C, about 20°C above T_g of poly(α-ethyl styrene). Contrary to expectations, the glass transitions of the 92/8, 33/67 poly(isopropenyl cyclohexane-co-methyl styrene) and poly(α-methyl styrene) are almost identical, as are the decomposition temperature ranges. Thermal data indicate that the decomposition mechanism of the copolymers and hydrogenated homopolymer is random scission. The thermogravimetric curves also indicate that the copolymers are random. Thus, chain stiffness appears not to increase rapidly with hydrogenation of this highly syndiotactic polymer.     

Piezoelectric relaxation in poly(γ-benzyl-glutamate)

The piezoelectric d- and e-constants, together with the elastic constant and the dielectric constant, were measured for oriented poly(γ-benzyl-glutamate) (PBG) films with various elongation ratios as a function of frequency and temperature, using an apparatus developed by us. The results are discussed in terms of a general theory of piezoelectricity for inhomogeneous systems, in particular for a disperse two-phase system. The piezoelectricity of PBG film is proved to originate from the piezoelectric and optically active symmetry of PBG crystallities and their orientation distribution by three findings: (1) the d₁₄ component of the piezoelectric matrix, which is the only component for a uniaxially or uniplanarly oriented system, is observed; (2) d₁₄ > 0 for PBDG and d₁₄ < 0 for PBLG; (3) d₁₄ is proportional to the degree of orientation F_c of PBG crystallites, as determined by x-ray diffraction. By extrapolating to perfect orientation, d₁₄ is determined to be 5 × 10^?8 cgs esu, if the side chains of PBG are rigid. The piezoelectric relaxation of PBG due to thermal motion of the side chains has a dual character: it is relaxational at lower frequencies and retardational at higher frequencies. On the assumption that the α-helical main chains surrounded by the bulky side chains are responsible for the origin of the piezoelectricity, such relaxation phenomena are interpreted in terms of the relaxation of the local elastic field in the main chains. An equivalent model having the same frequency characteristics is proposed to include the higher order structure of the PBG film.     

Crystal structure of poly(γ-methyl L-glutamate) at high temperature

A unique crystal structure of the α-helical form of poly(γ-methyl L -glutamate) appearing above 170°C is analyzed by x-ray diffraction. At room temperature, the unit cell determined for a well-annealed sample is hexagonal with dimension a = 11.8₂ Å and contains one α helix with pitch P = 5.42 Å and unit height p = 1.493 Å. This form is reversibly transformed at about 170°C into a modification characterized by a trigonal unit cell (a = 21.2₇ Å) having three times the cross section of the single-chain unit cell and containing three α helices with P = 5.50 Å and p = 1.504 Å. In a narrow temperature range below 180°C, the three chains in the unit cell are not interrelated by any crystallographic symmetry element, but they are reasonably associated with one another so that all helices are surrounded by other helices in the same way. The axial and azimuthal displacements between neighboring chains are expressed by z = ±4p/3 and ? = ± (2π/3)(4p/P ? 1), respectively. The segmental main-chain motion, which becomes appreciable above 150°C, is composed of screw-type motion along the α-helix fold and correlated P/3 axial jumps. The relation between the structural transition and thermal motion is discussed.     

Piezoelectric relaxation in poly(γ-methyl-L-glutamate) at high temperature

Piezoelectric relaxation has been studied on elongated poly(γ-methyl-L-glutamate) films with the α-helical molecular conformation. Relaxation processes are observed near 0 and 100°C. Each process has a dual character composed of relaxational and retardational frequency dependences. The low-temperature process is ascribed to thermal motion of side chains. The high-temperature process, discussed in relation to the dielectric relaxation, is attributed to the ionic dc conduction connected with the two-phase structure of crystalline regions and the electrode polarization.     

Synthesis of poly(γ-methoxypropylmethylsilylene) and poly(γ-methoxypropylmethylsilylene-co-di-n-hexylsilylene)

The synthesis of γ;-methoxypropylmethyldichlorosilane, and its subsequent polymerization and copolymerization with di;-n;-hexyldichlorosilane through the reductive coupling with sodium has been accomplished. The resulting polymers contain methyl ether side groups that allow further synthetic transformations on the polysilane backbone. For poly (γ;-methoxypropylmethylsilylene) these groups impart solubility characteristics different than typical alkyl and aryl substituted polysilanes. These new polymers and copolymers have been characterized by GPC and ¹H-, ¹³C-, and ²⁹Si-NMR. © 1994 John Wiley & Sons, Inc.     

Thermal and transport properties of copoly(γ-stearyl L-glutamate-γ-methyl L-glutamate)

Copoly(γ-stearyl L-glutamate-γ-methyl L-glutamate)s with various compositions were synthesized by ester exchange of poly(γ-methyl L-glutamate) with stearyl alcohol. The temperature dependence of the volume and helical spacing of the copolyglutamates thus prepared was examined from 0 to 100°C, observing the melting and crystallization of the long alkyl side chain attached to the polypeptide backbone. The melting temperature of the long side chain increased with increasing stearyl L-glutamate content. With increasing temperature, the α helical spacing decreased, especially with the melting of the side chain. On the other hand, the volume increased with increasing temperature and a marked increase was observed on melting. The above two phenomena were elucidated according to the structural model of the long side chain of the copolyglutamates proposed here. The transport properties, permeability coefficients were found to be considerably affected by the side-chain structure of the copolyglutamate and by the melting or crystallization of the side chain. The permeability coefficient of the copolyglutamate with 67% degree of stearylation, varied as much as two orders of magnitude before and after melting or crystallization. It was also confirmed that the permeability coefficient is controllable by the side-chain structural change of polypeptides.     

Piezoelectric properties of oriented deoxyribonucleate films

The piezoelectric effect due to shear in oriented films of DNA is strongly dependent on the relative humidity at which the films are equilibrated. Below about 60% relative humidity, the sign of the piezoelectric modulus is negative and its magnitude passes through a maximum with increasing temperature. This type of polarization appears to be due to the stress-induced orientation of dipoles in sugar-phosphate main chain. Above 75% relative humidity, water molecules are adsorbed by the bases and stabilize the ordered structure of double strand helices. In this crystalline state, the sign of the piezoelectric modulus is positive and its magnitude decreases markedly at about?75°C. This type of polarization appears to be due to the stress-induced orientation of dipoles in bases attached to the main chain. From comparisons between piezoelectric, elastic, and dielectric measurements, it is concluded that the piezoelectric relaxation observed at?75°C and 75% relative humidity is mainly due to the dielectric relaxation of the bases in the double helix.     

New technique of processing highly oriented poly(vinylidene fluoride) films exclusively in the β phase

Oriented β‐phase films were obtained by utilizing two different techniques: conventional uniaxial drawing at 80 °C of predominantly α‐phase films, and by drawing almost exclusively β‐phase films obtained by crystallization at 60 °C from dimethylformamide (DMF) solution with subsequent pressing. Wide angle X‐ray diffraction (WAXD) and pole figure plots showed that with the conventional drawing technique films oriented at a ratio (R) of 5 still contained about 20% of phase α, a crystallinity degree of 40% and β‐phase crystallographic c ‐axis orientation factor of 0.655. Drawing at 90 °C and with R = 4 of originally β‐phase films results in exclusively β‐phase films with crystallinity degree of 45% and orientation factor of 0.885. Crystalline phase, crystallinity degree, and crystallographic c‐axis orientation factor of both phases were also determined for α‐phase oriented films obtained by drawing α‐phase films at 140 °C. For films drawn at 140 °C the α to β phase transition drops to about 22%. Reduction in crystallinity degree with increasing R is more pronounced at draw temperature of 140 °C compared with 80 °C. Moreover, for both phases the c ‐axis orientation parallel to the draw direction is higher at draw temperature of 140 °C than at 80 °C. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2793–2801, 2007     

A structure with an irregular layer lattice in poly(γ-methyl L-glutamate-co-γ-benzyl L-glutamate) film

Two types of films showing different characteristic x-ray equatorial patterns were prepared from chloroform and N,N-dimethylformamide solutions of poly(γ-methyl L -glutamate-co-γ-benzyl L -glutamate). In the film cast from chloroform solution, the x-ray pattern on the equator consisted of a remarkable mixture of sharp and diffuse reflections, with the sharp reflections corresponding to integral values of 1/3k. On the other hand, in the film cast from N,N-dimethylformamide solution, a well-defined x-ray pattern was observed. An explanation for this characteristic pattern of chloroform-cast film was made on the basis of a structural model wherein stacking faults or dislocations are incorporated into the ordered structure characteristic of N,N-dimethylformamide-cast film. Two domains divided by a stacking fault are mutually displaced along the (100) crystal planes, but the shape and size of the unit cell is everywhere the same. The intensity distribution of x-ray diffraction was calculated as a function of the probability of a stacking fault occurring in a regular sequence of (100) planes. The best correspondence with observation was obtained with a stacking fault in every three layers, on the average.     

Effect of γ irradiation on the surface properties of wet polysulfone films containing poly(vinylpyrrolidone)

In Japan, hemodialyzers are usually sterilized by γ irradiation. However, the polymer materials used in the dialysis membrane, such as polysulfone (PSf) and poly(vinylpyrrolidone) (PVP), undergo crosslinking or degradation on exposure to γ radiation. In the present study, we prepared PSf/PVP films (PVP content, 0–50 wt%) and used atomic force microscopy (AFM) to perform nanoscale evaluations of the effect of γ irradiation (25 and 50 kGy) on the surface properties of wet PSf/PVP surfaces. Force‐curve measurements were used to evaluate the hardness of and fibrinogen adsorbability on the wet PSf/PVP surface; fibrinogen adsorbability on the wet PSf/PVP surface was evaluated using AFM probes with fibrinogen immobilized on the tips of the probes. At PVP levels greater than 5 wt%, the wet PSf/PVP film surface was completely covered with hydrated and swollen PVP particles. The surface hardness of the wet PSf/PVP films exposed to 25‐kGy γ irradiation greatly decreased with increasing PVP content, whereas the surface hardness of the wet PSf/PVP films exposed to 50‐kGy γ irradiation did not decrease significantly. At higher PVP levels, the reduction in the fibrinogen adsorbability on a wet PSf/PVP film exposed to 25‐kGy γ irradiation was more significant than that on a wet PSf/PVP film exposed to 50‐kGy γ irradiation. PVP particles on the wet PSf/PVP film surface exposed to 50‐kGy γ irradiation did not show significant hydration and swelling because the polymer materials PVP–PSf and PVP‐PVP in these membranes has undergone excessive crosslinking due to γ irradiation. Copyright © 2010 John Wiley & Sons, Ltd.     

Directional anisotropy of dielectric β-relaxation in oriented poly(ethylene terephthalate)

The dielectric β-relaxation in oriented poly(ethylene terephthalate) was investigated over wide ranges of frequency and temperature, with the electric field applied at inclinations of 0°, 45°, and 90° to the draw direction. Pronounced directional anisotropy is observed over the entire range of temperature and frequency. With the external field parallel to the draw direction the dielectric loss is considerably smaller than the value obtained with the field normal to the draw direction. The value obtained with the electric field at 45° to the draw direction is intermediate between the other two. On the other hand, the activation energy is largest for 0° inclination and smallest for 90° inclination. It is suggested that motions of the dipoles involve localized rocking of the molecular chain backbone, particularly when the external electric field is parallel to the chain direction.