Tamaichi Ashida

Crystallization of block copolymers: 3. Crystallization behaviour of an ε-caprolactone-butadiene diblock copolymer

Abstract The crystallization behaviour of an e-caprolactone-block-butadiene diblock copolymer was observed by small-angle X-ray scattering employing synchrotron radiation. The processes of primary and secondary crystallizations were separately analysed by procedures usually used for homopolymer crystallization, and were compared with the case of a poly(e-caprolactone) homopolymer (PCL). The Avrami analysis at the primary crystallization showed an exponent n ranging from 2 to 3. This value is comparable to n evaluated for PCL and also n widely reported for crystalline homopolymers, indicating that the crystallization of the PCL block drives the primary stage without the influence of the existing microphase structure of the block copolymer. In the secondary crystallization, on the other hand, the rate was significantly retarded when a microphase structure existed in the system.

Morphology and crystal structure of an a axis oriented, highly crystalline poly(ethylene terephthalate)

Abstract The morphological structure of an extremely highly crystalline poly(ethylene terephthalate) (PET) which was obtained by very long term annealing after direct esterification was characterized by small angle and wide angle X-ray diffraction, infra-red spectroscopy, and density and fusion measurements. The specimen has a high melting point of 302.5°C, an observed density of 1.468 g cm−3 and a calculated density of 1.501 g cm−3. From these results, together with small angle X-ray scattering data and the dependence of the fusion curves on the heating rate, this highly crystalline material is proposed to consist of molecules which are either fully extended or which contain only a few folds. Moreover, the specimen has a good double orientation: the crystallites not only have their a axes parallel, but also have their (001) planes approximately parallel to the main plane of the specimen. The structure determined from the X-ray diffraction intensity data is basically consistent with that obtained by Daubeny et al.

Small-angle X-ray scattering study of the morphology of blends of poly(ε-caprolactone) and polystyrene oligomer

Abstract A small-angle X-ray scattering (SAXS) study was carried out to investigate the morphology of blends of poly(e-caprolactone) (PCL) and polystyrene oligomer (PSO) when the former component was crystallized. This PCL-PSO system shows an upper critical solution temperature type of phase diagram. For blends with ф PCL ( ф PCL is the weight fraction of PCL), the scattering observed is the superposition of the intensities arising from the crystalline region (made up by alternate stacking of lamellae and thin amorphous layers) and from the inhomogeneity in the system (due to the crystalline regions and the amorphous domains). For blends with ф PCL > 0.8 , only scattering from the crystalline region was observed. From the SAXS curve, the lamella thickness lc, the amorphous layer thickness la and the linear crystallinity χc of the crystalline region were obtained on the basis of the Hosemann-Tsvankin model. The value of lc was 5.5 nm independent of composition, while la and χc were 8.1 nm and 0.4 for blends with ф PCL but varied linearly with composition for blends with ф PCL > 0.8 . These parameters were also studied by the correlation function from Vonks model.

Crystallization behaviour of a microphase-separated diblock copolymer

Abstract The crystallization behaviour of a microphase-separated diblock copolymer, ϵ-caprolactone-block-butadiene (PCL-b-PB), was observed by small-angle X-ray scattering employing synchrotron radiation. The Avrami analysis at the early stage of crystallization did not show any significant difference between PCL-b-PB and a poly(ϵ-caprolactone) homopolymer (PCL), suggesting that the initially existing microphase structure does not affect the early stage of crystallization. In the late stage, the crystallization of PCL-b-PB was significantly retarded compared to the case of PCL, and the rate was dependent on the microphase structure and/or molecular characteristics of the copolymer.

Formation of Anisotropic Phase of Low-molecular-weight Poly(γ-benzyl-l-glutamate)s in Solution

Abstract Low-molecular-weight poly(γ-benzyl-l-glutamate)s having degrees of polymerization (D. P.) 4 and 8 give an anisotropic phase in ethylene dichloride, if the concentration is appropriately chosen and the solution is incubated at a suitable temperature range. The optimum condition of concentration and temperature is more restricted for D. P. 8 than for D. P. 4. Ethylene dibromide solutions of the D. P. 4 specimen also give an anisotropic phase at some conditions. Infrared spectra and x-ray diffraction together with polarized microscopic observations suggest that the anisotropic phase consists of the β-structure of antiparallel arrangement of extended polypeptide chains; it has regular sequences of chains in the main chain direction and a stack of β-sheets in the side chain direction.

Morphology formed in binary blends of poly(ε-caprolactone) and ε-caprolactone-butadiene diblock copolymer

Abstract The morphology formed in binary blends of poly(e-caprolactone) (PCL) and e-caprolactone-butadiene diblock copolymer (PCL-b-PB) has been investigated by small-angle X-ray scattering (SAXS). The difference in the microdomain structure in the melt yielded different morphologies after crystallization: when PCL dispersed uniformly in the PCL domain in the melt, the morphology was an alternating structure composed of lamellane and amorphous layers (lamellar morphology). When PCL was localized within the PCL domain, a mosaic structure of two lamellar morphologies, each consisting of a PCL region and a PCL-b-PB-rich region, was formed over a limited composition range.

Absolute stereochemistries and conformations of clerodin and caryoptin. Why conflicting results in absolute stereochemistry based on CD and ORD spectra

Abstract The reverse of absolute stereochemistries of clerodin and caryoptin means that the correct chirality conflict with the absolute stereochemistries based on Cotton effects. Molecular mechanics and X-ray studies confirmed that the B ring of the 6-keto derivatives retained the boat form as the stable conformer. Furthermore, the steric factors causing the conformational changes were proved by derivation to the strain-free derivatives. The conformation of the B ring in the derivatives changed to the chair form which is confirmed by the X-ray and CD.

Roles of lysine‐69 in dimerization and activity of Trimeresurus flavoviridis venom aspartate‐49‐phospholipase A2

Trimeresurus flavoviridis (Habu snake) venom aspartate‐49‐phospholipase A2 (Asp‐49‐PLA2) was reacted at pH 9.0 with a 2‐fold molar excess of 2,4,6‐trinitrobenzenesulfonate in the absence of Ca2+ and two trinitrophenylated derivatives were isolated by HPLC. One was a derivative modified at Lys‐11 and its activity was mostly retained. The other was a derivative modified at both Lys‐11 and Lys‐72 and its activity was 40% that of unmodified enzyme. Trinitrophenylation of Lys‐72 appeared to bring about a conformational disorder at the lipid‐water interface recognition site and thus a reduction of activity. When the enzyme was modified in the presence of Ca2+, activity decreased at a rate much faster than that in the absence of Ca2+ and Lys‐69 came to be modified. These results suggested that conformational displacement of Asp‐49‐PLA2 of a local to global type occurs upon the binding of Ca2+. The derivative modified at Lys‐69 had 28% activity and existed as a monomer. This supports a previous assumption that Lys‐69 participates in dimerization of group II Asp‐49‐PLA2s [Brunie et al. (1985) J. Biol. Chem. 260, 9742–9749] and shows that dimerization is not necessarily essential for activity manifestation.

Crystallization and preliminary X-ray studies on the trypsin inhibitor I-2 from wheat germ and its complex with trypsin

A Bowman-Birk type trypsin inhibitor I-2, M(r) = 14 000, 123 amino-acid residues, isolated from wheat germ, and its complex with trypsin have been crystallized. For I-2 two morphologically different crystal forms were obtained. Crystal form 1 is tetragonal, P4(1)22 or P4(3)22, with a = 55.45 (2), c = 129.1 (2) A and V = 3.97 (2) x 10(5) A(3). The crystals diffract X-rays very anisotropically, to less than 6 A resolution normal to the c* direction, but up to 3 A resolution in the other directions. Crystal form 2 is monoclinic, space group C2. The cell parameters show significant variation even for crystals in the same batch. The median parameters are: a = 83.9, b = 41.5, c = 45.7 A, beta = 95.9 degrees and V = 1.58 x 10(5) A(3). The diffraction pattern is isotropic and reflections up to 2.2 A resolution were observed. The crystals of the complex between bovine trypsin and I-2 (2:1) belong to the orthorhombic space group P2(1)2(1)2(1) with a = 73.49 (2), b = 120.56 (3), c = 70.04 (2) A and V = 6.206 (5) x 10(5) A(3). The crystals diffract up to 2.3 A resolution, and contain one complex of 60 100 Da in an asymmetric unit.

Crystallization and preliminary X-ray analysis of β-­amylase from Bacillus polymyxa

A truncated beta-amylase (E.C. 3.2.1.2) from Bacillus polymyxa has been crystallized using the hanging-drop vapour-diffusion method at 277 K. The crystals belong to the orthorhombic space group P212121 with cell dimensions a = 64.6, b = 141.9, c = 155.1 A and diffract to 2.5 A resolution. The asymmetric unit containing three protein molecules was derived from an electron-density map calculated at 4 A resolution using MIR phases. This gives a Vm value of 2.36 A3 Da-1.