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.     

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.     

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.     

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.     

Crystal transition and structure of poly (γ-n-alkyl glutamate)s

The nature of the crystal transition of the α-helical forms of poly (γ-n-alkyl glutamate)s (alkyl = ethyl, propyl, and butyl) is described. The transition is thermally reversible, and its temperature T₂ is much higher than the glasslike transition temperature T₁ associated with the side-chain motion. The main chains undergo large-scale motion (librational about the chain axis and translational along the axis) above T₃ ≈ 200°C. The structure observed below T₂ is anomalously disordered compared with that observed between T₂ and T₃. The crystal structure emerging above T₂ is analyzed for a typical sample of poly(γ-n-propyl L -glutamate). The trigonal unit cell contains three α-helices so that each helix is surrounded by other helices in the same fashion, but the helices are not interrelated by a crystallographic symmetry element. The side chains suffer no particular change at T₂. The main-chain motion gives rise to the T₂ transition by inducing attractive forces between interpenetrating side chains.     

A crystal transition in poly(γ-n-alkyl L-glutamate)s

A thermally reversible crystal transition was found for γ-helical poly(γ-n-alkyl L -glutamate)s (alkyl = ethyl, propyl, butyl, and amyl). The transition temperature is higher than that of the side-chain mechanical dispersion, and decreases from 115 to ?5°C, as the alkyl groups become longer. The transition in poly(γ-n-propyl L -glutamate) is clearly first order. The structures were analyzed by x-ray diffraction at various temperatures. It is noteworthy that the pseudohexagonal form observed below the transition temperature is less ordered than the hexagonal form at higher temperatures. The mechanism of this transition is discussed.     

Growth stages in epitaxial crystallization of poly(γ-benzyl L-glutamate)

The electron microscope study of the isothermal epitaxial crystallization of PBLG on 001 cleavage surface of NaCl or KCl from 0.01% chloroform solution with various n-octane contents has shown that the epitaxial growth process could be divided in two stages. In the first stage a rapid growth of a lamellar layer 20–40 Å thick could be observed; the PBLG molecules in αhelix conformation are oriented along <110> substrate directions. The dimensions and perfectness of alignment of these lamellae along the <110> direction depends on the molecular weight of the PBLG. In the second stage of PBLG epitaxial crystallization the relatively slow thickening of some initial lamellae takes place and one can observe many types of secondary structures. With increasing thickness of the epitaxial structures and increasing molecular weight of the PBLG the degree of orientation in relation to <110> substrate direction diminishes. The two growth stages in PBLG epitaxial crystallization are related to different kinds of orienting and attracting forces of the alkali halide substrate.     

Piezoelectric properties of oriented films of poly(γ-methyl D-glutamate)

The dynamic piezoelectric stress constant e^*₂₅ of drawn films of poly(γ-methyl D -glutamate) (PMDG) cast from solutions in α-helix-promoting solvents 1,2-dichloroethane (DCE) and chloroform and from the nonhelicogenic solvent dichloroacetic acid (DCA) was measured from ?180°C to 200°C at 110 Hz. The drawn and annealed films cast from chloroform show a small peak for the real part of piezoelectric stress constant ?e′₂₅ in the temperature range of the mechanical α₂-crystalline relaxation, which is caused by the distortion motion of the backbone chain of the α-helix. On the other hand, drawn films cast from DCE show the peak of the real part of the piezoelectric stress constant, whose magnitude decreases in the range of the mechanical α₁-crystalline relaxation or the β-relaxation processes, which were previously ascribed, respectively, to mutual slipping of α-helices and to the micro-Brownian motion of disordered regions. Also, ?e′₂₅ becomes virtually zero near 180°C where the α₂-relaxation is located. These results suggest that the polarization change induced by applied strain is caused by distortion of the backbone chains in the α-helix. Near 0°C, the temperature range of the side-chain mechanical relaxation, ?e′₂₅ exhibits a marked peak both for films cast from chloroform and from DCE. The maximum value of ?e′₂₅ and the orientation function of the α-helix axis are linearly related and extrapolation of ?e′_25,max to unit orientation function gives 1.3 × 10⁴ cgs esu which corresponds to 2.4 Debye per residue. This value corresponds reasonably to the value of 3.71 Debye for the permanent dipole moment of NHCO bond if the correction for crystallinity is made. This result also indicates the piezoelectric properties of PMDG arise from distortion of the backbone chain of the α-helix induced by applied strain.     

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.     

Reactive polypeptides. II. Photochemistry of poly(γ-cinnamyl L-glutamate)

Poly(γ-cinnamyl L -glutamate) was irradiated in the presence and absence of benzophenone in dichloroethane. The irradiated polymers were analyzed by gas chromatography after hydrolysis. It was possible to assign the transformation in the presence of benzophenone to trans-cis photoisomerization by comparing the effects with those observed for a model compound cinnamyl acetate. The equilibrium composition of cis and trans isomers in the photostationary state was similar for the model compound and the polypeptide. Photoisomerization was found to be accompanied by marked side reactions for the direct irradiation. Circular dichroism spectra were empolyed to study the structure, and no changes in the structure were found for the irradiated polymers.     

Structural differences between two crystal modifications of poly(γ-benzyl L-glutamate)

X-ray diffraction patterns were obtained for as-cast and oriented films of poly(γ-benzyl L -glutamate) and a comparison was made of the molecular packing of the α-helices in forms B and C. Form B snowed Bragg reflections on the layer lines as well as on the equator. The spacings were explained by a monoclinic unit cell comprising two chains, with a = 29.0₆ Å, b = 13 2₀ Å, c = 27.2₇ Å α = γ = 90°. and β = 96°. The chains contained in this unit cell and consequently alternating in the crystal have opposite chain directions. Form C showed continuous scattering on the layer lines and reflections on the equator. This form, therefore, is a nematiclike paracrystal in which the packing of α-helices is periodic in the direction lateral to the chain axis (a = 14.8–115.2 Å, b = 14.3–14.8 Å, c = 27 Å, and γ = 118°–120°), but the relative levels of the chains along the chain axes are displaced. The formation of form C may be attributed to random placement of two chains with mutually opposite chain directions.     

Crystal structure of poly(ω‐pentadecalactone)

The crystal structure of poly(ω‐pentadecalactone) (PPDL) synthesized by enzyme‐catalyzed polymerization was determined by full‐profile refinement. A pseudo‐orthorombic monoclinic unit cell with dimensions a = 7.49(1), b = 5.034(9), and c = 20.00(4)Å (fiber axis), and α = 90.06(4)° hosts two monomeric units belonging to polymer chains with opposite orientation, according to the P2₁ space‐group symmetry. A close similarity to the crystal structure of poly(?‐caprolactone) was evident. However, the even number of backbone atoms in the monomer unit of PPDL leads to a lower crystal symmetry. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1009–1013, 2003     

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.     

Polymerization of β‐pinene with Schiff‐base nickel complexes catalyst: Synthesis of relatively high molecular weight poly(β‐pinene) at high temperature with high productivity

A series of easily accessible and stable Schiff‐base nickel complexes (complex 1 – 4 ) in conjunction with methylaluminoxane (MAO) were employed for the synthesis of relatively high molecular weight β‐pinene polymers at high temperature with high productivity. The ligand structure of the complex had a substantial effect on the polymerization in terms of the productivity and the molecular weight. With complex 4 in the presence of MAO, high molecular weight polymers of β‐pinene (M_n ～ 10,900) were obtained at 40 °C with an extremely high productivity up to 1.25 × 10⁷ g polyβ‐pinene/mol of Ni. ¹H NMR analyses showed that the obtained β‐pinene polymer was structurally identical to that formed by conventional cationic Lewis acid initiators. The polymerization was presumably initiated by the nickel cation formed by the reaction of the schiff‐base nickel complex and MAO, while the propagation proceeded in a manner typical for a conventional carbocationic polymerization process. Direct evidence for the carbocationic polymerization was offered by the fact that quenching of the polymerization with methanol at a low monomer conversion resulted in incorporation of a methoxyl end group into the polymer chain. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3739–3746, 2007