Yozo Chatani

Structural studies of polyesters: 5. Molecular and crystal structures of optically active and racemic poly (β-hydroxybutyrate)

Abstract The molecular and crystal structure of naturally occurring optically active poly(β-hydroxy-butyrate) was analysed by X-ray diffraction. The unit cell is orthorhombic, P2 1 2 1 2 1 -D 4 2 , with a = 5·76 A , b = 13·20 A , and c( fibre period )=5·96 A and two molecules pass through the unit cell. The molecule has a conformation shown by the Fischer projection for the case of a rectus polymer, giving a left-handed ( 2 1 ) helix. The crystalline synthesized racemic polymer gave the same X-ray diffraction pattern as the naturally occurring optically active polymer. This result indicates that the racemic polymer has an isotactic configuration and consists of two kinds of crystallites, each composed only of the left-handed helices of rectus polymer chains, or only of the right-handed helices of sinister polymer chains.

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.

Phase Transition and Structure Change of Urea Adducts with n-Paraffins and Paraffin-type Compounds

Abstract The phase transition temperatures of urea adducts with many n-paraffins and several paraffin-type compounds were measured by differential thermal analysis and the general structure change causing the phase transitions was revealed by X-ray structure analysis. The ordinary hexagonal adducts (high-temperature form) transform commonly into orthorhombic adducts (low-temperature form) except for a few adducts with guest molecules possessing cylindrical shapes. The phase transition can be regarded as an order-disorder transition with respect to the orientation of the guest molecules about the urea channel axis with a cooperative deformation of the urea channels resulting in the orderly orientation of guest molecules below the transition temperatures. The changes in orientation and motion of the guest molecules through the phase transitions are discussed on the basis of X-ray analysis, potential energy and broad-line NMR.

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.

Structural change of st-PMMA on drawing, absorption and desorption of solvents

Abstract Well-oriented crystalline samples of syndiotactic poly(methylmethacrylate) (st-PMMA) could be prepared from stretched non-crystalline samples on solvent-induced crystallization using chloroacetone, diethyl ketone, etc. as the solvent. X-ray fibre diagrams of these samples usually show period of 35.4A and also suggest that the st-PMMA chains have a helical conformation of large radius and small axial pitch along the original stretched direction. Inversion of dichroism for most infra-red absorption bands during the crystallization, which is an indication of a wide variation in the orientation of the chains, again supports the large helical conformation. It was also confirmed that the solvents are necessary in maintaining the crystalinity as the samples lose crystallinity on desorption of the solvents. From these results, it is conceivable that st-PMMA forms a complex with the solvents similar to the well-known amylose-iodine complex.

X-ray crystallographic study of solid-state polymerization of trioxane and tetraoxymethylene

Abstract An X-ray study has been applied to clarify the relationship between crystal structures and crystal orientations of tetraoxymethylene and polyoxymethylene obtained by solid- state polymerization of tetraoxymethylene. The polyoxymethylene crystal obtained by the solidstate polymerization of a tetraoxymethylene single crystal was found to be definitely oriented with respect to the original tetraoxymethylene single crystal without any aftertreatment; i.e., the polymer chain (the c-axis) is parallel to the b-axis of tetraoxymethylene and the a-axis of polyoxymethylene coincides to the c-axis of tetraoxymethylene. In addition to the main orientation, other preferred crystalline orientations (“twin structure”) of polyoxymethylene were observed in polymers polymerized at lower temperatures (60-80°C); i.e., the polymer chains are parallel to either the [100], [001], or [101] direction of the original tetraoxymethylene crystal, though the amount of such oriented crystallites is small. The twin structure is...

Structure of polyethylene sulfide

Abstract The structure of the polyether series expressed by the general formula [─(CH2)m─O─]n with m = 1-4, 6, 8-10, and 12 was previously determined [l]. The molecular structure of polyoxymethylene (m = 1) is a sequence of nearly gauche forms (9/5 o r 29/16 helix [a]). On the other hand, the conformation of polythiomethylene, the first member of the polythioether series [─(CH2)m ─S─]n, was found to also be a nearly gauche sequence (l7/9 helix) by Carrazzolo and Valle [3]. Both of these polymers have the highest melting point of each series (polyoxymethylene, 180°C; polythiomethylene, 245°C). Polyethylene oxide (m = 2) is a 7/2 helix consisting of nearly trans, trans, and gauche forms and has rather a low melting point (66°C). Polyethylene sulfide has a very high melting point (210°C) compared with polyethylene oxide. In this respect it is thus of much interest to investigate the structure of polyethylene sulfide. Boileau et al. [4] synthesized high molecular weight polyethylene sulfide and reported its u...

The crystal structure of isotactic poly(methyl methacrylate) : packing-mode of double stranded helices

Abstract The X-ray structure analysis of isotactic poly(methyl methacrylate) was performed by adopting the 10 1 double-stranded helix model as the molecular model, and the crystal structure analysis, which has remained as an unsettled problem for a long time, has been brought to an end. The crystals are orthorhombic, with rather large cell dimensions, i.e. a = 41.96, b = 24.34, and c ( fibre axis ) = 10.50 A . There are eight 10 1 double-stranded helices of the right-handed and left-handed senses in the unit cell, which take up a slightly complicated hexagonal-like closest packing-mode, and where among the first six neighbour helices the two same-handed senses are located at z = c 2 and the four opposite-handed senses are located at z = c 4 and 3c 4 . The space group is Fddd-D2h24 for the disordered structure, which is composed of upward and downward helices related by a twofold rotation axis perpendicular to the helix axis. This complicated helical packing-mode originates from (i) the fact that iPMMA as synthesized is an apparently racemic polymer, and (ii) the fact that two molecular chains form a robust and rod-like 10 1 double-stranded helix.

A preliminary X-ray study on ferroelectric phase transition of poly(vinylidene ruoride) crystal form I

SummaryFerroelectric phase transition of poly(vinylidene fluoride) crystal form I has been investigated by X-ray diffraction measurements. The X-ray reflections of form I decrease in intensity steeply in the vicinity of 172°C and new reflections of the high-temperature phase, the conformation of which is essentially equivalent to that of form III (T3GT3¯G), begin to appear, maximize in intensity at about 183°C, and disappear above 190°C. These phenomena are consistent with the previously reported infrared spectral data. The X-ray reflections observed for the high-temperature phase contain the (100), (120), etc. forbidden for polar form III, suggesting a possibility of another crystal structure of anti-polar or non-polar form III.

Solid-state polymerization of pentoxane (─CH2─O─)5

Abstract In the course of systematic study of the solid-state polymerization of the cyclic oligomers of formaldehyde (─CH2─O─)m, it was found that pentoxane (─CH2─O─)5 undergoes polymerization in the solid state to form polyoxymethylene (─CH2─O─)n by X-irradiation. The present article contains (a) the molecular and crystal structure determination of pentoxane, (b) the determination of the relative crystal orientation of pentoxane and the resultant polyoxymethylene, and (c) some discussions on the role played by the crystal structure of pentoxane in the solid state polymerization comparing with the cases of trioxane and tetraoxane. Pentoxane forms an orthorhombic crystal. The crystallographic data are a = 8.194 A, b = 10.691 A, c = 7.682 A, D14 2h - Pbcn, four molecules in the unit cell. The relative crystal orientation of pentoxane and polyoxymethylene was determined using X-ray diffraction from single crystals of pentoxane which were partially converted into polyoxymethylene by X-irradiation. The polyoxy...