Ryosuke Kusumi

Cellulose Ester-graft-poly(ε-caprolactone): Effects of Copolymer Composition and Intercomponent Miscibility on the Enzymatic Hydrolysis Behavior

Enzymatic hydrolysis was conducted with Pseudomonas lipase for film samples of graft copolymers of cellulose acetate (CA) and butyrate (CB) with poly(epsilon-caprolactone) (PCL), CA-g-PCL, and CB-g-PCL, respectively. The two trunk polymers CA and CB, both having the degree of acyl substitution (DS) of >2, are respectively immiscible and miscible with PCL. A hindrance effect of the cellulose ester trunks on the enzymatic attack to the PCL component was observed for the two copolymer series; the situation was more conspicuous in the use of CB trunks. After the selective hydrolytic degradation of the PCL component, a topographical study by AFM revealed that the CA and CB constituents as residues formed a protuberant structure on the surface of the respective film specimens. The altitude and regularity of the protuberances were variant depending on the initial copolymer composition. In a phase-imaging mode of AFM, a hydrolyzed film of CA-g-PCL with an extremely low graft-density (acetyl DS > 2.95) showed particularly larger CA domains of >25 nm in diameter. The domain sizes were in accordance with a heterogeneity scale in the original intercomponent mixing state estimated by (1)H spin-lattice relaxation time (T(1)(H)) measurements in solid-state (13)C NMR spectroscopy. The present results demonstrate a high potential in application of the PCL-grafted cellulosic copolymers as spatiotemporally biodegradation-controllable materials.

Chemical shift tensor determination using magnetically oriented microcrystal array (MOMA): 13C solid-state CP NMR without MAS

Chemical shift tensors for the carboxyl and methyl carbons of L-alanine crystals were determined using a magnetically oriented microcrystal array (MOMA) prepared from a microcrystalline powder sample of L-alanine. A MOMA is a single-crystal-like composite in which microcrystals are aligned three-dimensionally in a matrix resin. The single-crystal rotation method was applied to the MOMA to determine the principal values and axes of the chemical shift tensors. The result showed good agreement with the literature data for the single crystal of L-alanine. This demonstrates that the present technique is a powerful tool for determining the chemical shift tensor of a crystal from a microcrystal powder sample.

Blends and Graft Copolymers of Cellulosics

This chapter is a general introduction to the present monograph and first describes the significance of the studies on “Blends and Graft Copolymers of Cellulosics” in the research field of compositional materials based on cellulose and related polysaccharides. Secondly, some technical key-terms and methods used for characterizing cellulosic blends and graft copolymers are explained. Finally, the outline of this book is provided by summarizing the main subjects of the constituting chapters with a perspective to tie together the subjects.

Crystal Orientation of Poly(l-Lactic Acid) Induced by Magnetic Alignment of a Nucleating Agent

The orientation of poly(l-lactic acid) (PLLA) crystals was controlled through crystal growth from a magnetically oriented nucleating agent, phenylphosphonic acid zinc (PPAZn). The one-dimensional magnetically oriented microcrystal array of PPAZn microcrystals revealed the relationship between the magnetization and crystallographic axes in the PPAZn crystal. The PPAZn microcrystals were homogeneously dispersed in PLLA via melt mixing, which decreased the molecular weight of the PLLA component due to degradation. The PPAZn microcrystals in the molten PLLA were uniaxially aligned under an 8-T static or rotating magnetic field. The wide-angle X-ray diffraction and small-angle X-ray scattering patterns of the PPAZn/PLLA composite films crystallized under each magnetic field showed that the PLLA lamellae grew from the surface of the PPAZn microcrystals, which were uniaxially oriented along the easy- or hard-magnetization axis, with the c-axis of PLLA parallel to the bc-plane of PPAZn. It was also suggested that the greater nucleating effect of PPAZn on PLLA was derived not from geometrical matching, but from factors such as favorable interactions and/or the plate-like shape of the microcrystal.

Cellulosic Polymer Blends 2: With Aliphatic Polyesters

This chapter presents a review of the authors’ studies on blends of cellulosic and chitinous polymers with a typical biodegradable polyester, poly(e-caprolactone) (PCL). A miscibility map is constructed for a series of cellulose ester (CE)/PCL blends as a function of the carbon number (N) in the acyl substituent of CE and the degree of substitution (DS). The map reveals that cellulose butyrate (CB), with N = 4, is miscible with PCL at a comparatively lower DS, owing to a structural similarity advantage for the ester side-group of CB with a repeating unit of PCL. The melt-crystallization behavior of PCL in the miscible blends is also described, and the observed slower kinetics is interpreted in terms of a thermodynamic diluent effect of the CE component. A similar miscibility characterization is made for a comparable series of acylated chitin (Acyl-Ch)/PCL blends. The blend miscibility of the chitinous series is generally lower owing to the concurrence of N-acylation at the C2 position than that for the cellulosic series. The tensile ductility and cytocompatibility are evaluated for selected Acyl-Ch/PCL blends with different degrees of miscibility and crystallinity, by using their thermally molded and alkali-treated films. The adaptability of the chitinous blends as cell-scaffolding materials is attainable by adequately controlling the mixing state of the polymer components.

Cellulosic Graft Copolymers

Graft copolymerization of cellulosics has been widely investigated to modify the polymer molecules and alter the surface properties of the bulk materials. While practical advantages for the graft copolymerization were found in the surface modifications, basic and systematic studies on the cellulosic molecular grafting were not conducted very well throughout the past century. One reason for the lesser amount of systematization work was the difficulty of elaborate synthesis involved in the controlled polymerization and product isolation and characterization for obtaining the target copolymers. However, since 2000, serious efforts have been made to tackle the formulation of the structure–property relationships at molecular and supramolecular levels and the material functionalization based on those elucidations. In this chapter, the authors review the progress in copolymerization and product isolation, molecular characterization, general thermal transition scheme, thermal treatment effect on the supramolecular structure development, molecular dynamics, and orientation characteristics, mainly for cellulose ester-graft-aliphatic polyesters. Examples of material functionalization include controlled biodegradation and modulation of optical birefringence for molded films of the graft copolymers.

Characterization of crystalline linear (1 → 3)-α- d -glucan synthesized in vitro

We investigated the crystal structure and molecular arrangement of the linear (1→3)-α-d-glucan synthesized by glucosyltransferase GtfJ cloned from Streptococcus salivarius using sucrose as a substrate. The synthetic products had two morphologies: wavy fibril-like crystals as major and thin lamellae as minor products. Their structures were analyzed using electron microdiffraction, synchrotron X-ray powder diffraction, and solid-state 13C NMR spectroscopy. The fibrils and lamellae had the same allomorphic form but different molecular arrangements. The wet crystals were in a hydrated form, which converted into an anhydrous form with a significant decrease in crystallinity on drying. The hydrated and anhydrous forms had an extended-chain conformation with 2/1 helix, and the hydrated form was estimated to contain one water molecule per glucose residue. The long glucan chains were folded in the fibril crystals, while the short, extended chains were arranged perpendicular to the base plane of the lamellae.

Single Crystal Solid-State NMR of Magnetically Oriented Powder

Solid-state NMR spectroscopy is one of the most widely used methods for investigating crystal structures, along with the X-ray and neutron diffraction methods. Solid-state NMR can provide structural information including isotropic chemical shift, dipolar and quadrupolar couplings, spin diffusion, and chemical shift tensor. Among these, the chemical shift tensor is of particular significance because the electronic environment around a nucleus is directly reflected on the chemical shift tensor. However, full information of the chemical shift tensor, including principal values and axes, is difficult to obtain experimentally because a large single crystal is required for the measurement. On the other hand, we have proposed the use of a magnetically oriented microcrystal array (MOMA) as an alternative to a single crystal.[1,2] A MOMA is a composite in which microcrystals are aligned three-dimensionally, prepared by using a time-dependent magnetic field. We recently demonstrated that the 13 C chemical shift tensors of L-alanine crystal can be completely determined by application of the standard procedure in the single-crystal rotation method to a MOMA of L-alanine microcrystals,[3] as shown in Figure 1. The L-alanine MOMA produces sharp resonance peaks without resolution enhancement by magic angle spinning (MAS). In addition, we observed that the positions of the 13 C resonance peaks vary systematically as a function of the angle ψ that is the sample-rotation angle about the axis inclined by the magic angle with respect to the NMR magnetic field. From the ψ-dependence of the chemical shifts, 13 C chemical shift tensor was completely determined. We confirmed that the combination of MOMA with the single-crystal rotation method can be applied to other nuclei such as 31 P and 15 N. These results clearly show that the MOMA method is a powerful tool for obtaining full information of the chemical shift tensor from a microcrystalline powder without MAS.