Showing papers by "Yoshiharu Kimura published in 2002"

Properties and Biodegradability of Polymer Blends of Poly(L‐lactide)s with Different Optical Purity of the Lactate Units

Abstract: Polylactides with high and low L-isomeric ratios of the lactate units (PLA99.0 and 77.0, where the numbers correspond to the L-ratios) ware melt-blended to analyze the changes in properties and biodegradability with the polymers blend. The crystallinity of the blends was almost similar to that of the blends of PLLA and PDLLA. The glass transition behavior supported the compatibility of both polymers. The glass transition behavior was indicative of a compatible nature of both polymers. The tensile modulus of the blends was almost identical irrespectively of the blend ratio, while their tensile strength decresed with decreasing composition of PLA99.0. Above T g , the storage modulus of the blends dropped from 2-3 × 10 9 Pa 1-3 × 10 6 Pa and then increased to a different level depending on the crystalline nature of the blends. The biodegradability of the blends increased with decreasing composition of PLA99.0. This difference in degradability can be well explained by our random packing model of local hedices of the L-sequenced chains for the l-rich PLA samples.

Macromolecular Organization of Poly(L‐lactide)‐block‐Polyoxyethylene into Bio‐Inspired Nano‐Architectures

Abstract: Block copolymers create various types of nano-structures, e. g., spheres, rods, cubes, and lamellae. This review discloses the dynamic macromolecular organization of block copolymers comprising poly(L-lactide) (PLLA) and poly(oxyethylene) (PEG) that allows to simulate elaborate biological systems. The block copolymers, AB- (PLLA-PEG) and ABA-type (PLLA-PEG-PLLA), are synthesized by ordinary lactide polymerization to have a controlled block length. They are dispersed into an aqueous medium to prepare nano-scale particles, consisting of hydrophobic PLLA and hydrophilic PEG in the core and shell, respectively. Then, the particles are placed on a flat substrate by the casting method. The particles are detected as discoids by AFM, having shrunk with loss of water. Heat-treatment of these particles at 60°C (above Tg of PLLA) gives rise to a collapse into small fragments, which then aggregate into bands with nano-size width and thickness. The PLLA-PEG bands align parallel to each other, while the PLLA-PEG-PLLA bands form a characteristic network resembling the neuron system created in animal tissue. As analyzed by TEM diffraction, each is composed of α-crystal of PLLA whose c-axis (molecular axis) is perpendicular to the substrate surface. Based on this fact, a doubly twisted chain structure of PLLA is proposed in addition to a plausible mechanism for the self-organization of the block copolymers. Derivatives of the PLLA-PEG block copolymers can form far more interesting nano-architectures. An equimolar mixture of enantiomeric copolymers, PLLA-PEG-PLLA and PDLA-PEG-PDLA, forms a hydrogel that is thermo-responsive. The terminal-modified poly(L-lactide)-block-polyoxyethylene monocinnamate (PLLA-PEG-C) forms a highly stabilized nanofiber by the photo-reaction of the cinnamates placed in the outer layer of the nanobands.

Mechanism of Enzymatic Hydrolysis of Poly(butylene succinate) and Poly(butylene succinate‐co‐L‐lactate) with a Lipase from Pseudomonas cepacia

Abstract: Enzymatic hydrolysis of poly(burylene succinate) (PBS) and poly (butylene succinate-co-L-lactate) (PBSL) has been studied by using a lipase originated from Paeudomonas cepacia. It has been found that the drawn fibers of PBSL are readily hydrolyzed by the action of the lipase, while, those of PBS undergo little enzymatic hydrolysis. Since the polymer films of PBS and PBSI are readily hydrolyzed under the same conditions, the enzymatic hydrolysis should depend not only on the crystallinity but also on the molecular orientation. The molecular weight of the samples gradually decreases with incubation time, because nonspecific hydrolysis occurs on the main chains of both PBS and PBSL even in the absence of lipase. The enzymatic hydrolysis of PBS and PBSL gives 4-hydroxybutyl succinate (HBS) as the main product with traces of succinic acid and butane-1,4-diol together with L-lactic acid in the case of PBSL. In addition, the hydrolysis rate of the carboxyl endcapped PBS is much slower than that of the original or hydroxyl end-capped PBS, These results imply a hydrolysis mechanism involving the preferential exo-type chain scission from the carboxyl terminals.

Dynamic mechanical properties of solution-cast poly(l-lactide) films

Abstract: Dynamic mechanical measurements were conducted on different kinds of poly( l -lactide) (PLLA) films to understand the transformation of internal structure of PLLA by both processing and annealing. Effects of annealing condition on the properties of PLLA films including crystallinity change were investigated by wide angle X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results from this study indicate that PLLA films made by both casting and pressing processes exhibit significantly different dynamic mechanical behavior and that the solvent casting process is relatively suitable for retention of mechanical properties because of the development of the crystalline phase even below the glass-transition temperature, T g . Moreover, the results of the dynamic mechanical analysis reveal a simpler relationship between the thermal history and the internal structure of the PLLA films prepared by solution casting, compared with that of PLLA films prepared by pressing.

Preparation of Nano-Particles of Poly(phenylsilsesquioxane)s by Emulsion Polycondensation of Phenylsilanetriol Formed in Aqueous Solution

Abstract: Spherical nano-particles of Poly(phenylsilsesquioxane) (PPSQ) were prepared by emulsion polymerization of phenylsilanetriol (PST) that had been formed in aqueous solution after hydrolysis of trichlorophenylsilane (TCP). The average size of the resultant particles was controlled from 30 nm to 110 nm in diameter by changing the amount of the emulsifier added to the solution. The PPSQ forming the particles was low molecular weight oligomer, consisting of silanol groups that can be utilized as functional groups for further chemical modification.

Method for decomposing polyesters containing aromatic moieties, a denier reduction method of fiber, and microorganisms having activity of decomposing the polyester

Abstract: A polyester containing aromatic moieties is contacted with microorganisms having the activity of decomposing the polyester to decompose or reduce it. Preferably, either or both of Trichosporon FERM BP-6445 or Arthrobacter FERM BP-6444 was contacted with the polyester to decompose or reduce it. A fiber made of the polyester or a cloth made of such fiber may be reduced by contacting it with the microorganisms having the activity of decomposing the polyester.

Properties and enzymatic degradability of melt-spun fibers of poly(butylene succinate) and its various derivatives

Abstract: Chain-extended poly(butylene succinate) (PBS-e) and poly(butylene succinate/adipate) (PBSA-e) as well as high polymers of poly(butylene succinate-co-carbonate) (PBSC) and poly(butylene succinate-co-e-hydroxycaproate) (PBSCL) were melt-spun into mono-filament fibers by the on-line spinning and drawing technique. The mechanical properties and degradability of these fibers were totally compared in reference to those of the poly(butylene succinate) homopolymer (PBS) and poly(butylene succinate-co-L-lactate) (PBSL). It was found that the tensile strength of the drawn fibers decreases in the order of PBSA-e» PBS-h> PBSL> PBS-e> PBSC> PBSCL corresponding with the decreasing order of their molecular weight. Their enzymatic degradability was studied with a lipase originated from Pseudomonas cepacia. It was found that the rate of enzymatic degradation is in the order of PBSA-e> PBSC> PBSL> PBSCL» PBS-e ≅ PBS-h. This rate difference can be explained by the difference in crystal size and the polarity effect of the comonomer units that may affect the accessibility of the enzyme to the polymer chains.

Macromolecular organization of poly(L-lactide)-block-polyoxyethylene into bio-inspired nano-architectures

Abstract: Review: Block copolymers create various types of nanostructures, e.g., spheres, rods, cubes, and lamellae. This review discloses the dynamic macromolecular organization of block copolymers comprising poly(L-lactide) (PLLA) and poly(oxyethylene) (PEG) that allows to simulate elaborate biological systems. The block copolymers, AB- (PLLA-PEG) and ABA-type (PLLA-PEG-PLLA), are synthesized by ordinary lactide polymerization to have a controlled block length. They are dispersed into an aqueous medium to prepare nano-scale particles, consisting of hydrophobic PLLA and hydrophilic PEG in the core and shell, respectively. Then, the particles are placed on a flat substrate by the casting method. The particles are detected as discoids by AFM, having shrunk with loss of water. Heat-treatment of these particles at 60 °C (above T g of PLLA) gives rise to a collapse into small fragments, which then aggregate into bands with nano-size width and thickness. The PLLA-PEG bands align parallel to each other, while the PLLA-PEG-PLLA bands form a characteristic network resembling the neuron system created in animal tissue. As analyzed by TEM diffraction, each is composed of α-crystal of PLLA whose c-axis (molecular axis) is perpendicular to the substrate surface. Based on this fact, a doubly twisted chain structure of PLLA is proposed in addition to a plausible mechanism for the self- organization of the block copolymers. Derivatives of the PLLA-PEG block copolymers can form far more interesting nano-architectures. An equimolar mixture of enantiomeric copolymers, PLLA-PEG-PLLA and PDLA-PEG- PDLA, forms a hydrogel that is thermo-responsive. The terminal-modified poly(L-lactide)-block-polyoxyethylene monocinnamate (PLLA-PEG-C) forms a highly stabilized nanofiber by the photo-reaction of the cinnamates placed in the outer layer of the nanobands.

Chemical Synthesis and Properties of Well‐defined Oligomeric Esters

Abstract: Introduction Historical Outline Synthesis and Properties of Oligomeric Polyesters Poly(butylene succinate) Poly(ɛ-caprolactone) Poly(3-hydroxybutyrate) Poly(glycolic acid) Poly(lactic acid) Poly(malic acid) Polyesters Synthesized by Enzymatic Polymerization Applications Industrial Uses Biomedical Uses Patents Keywords: aliphatic polyester; chain extender; drug delivery system; enzymatic polymerization; guided tissue engineering; poly(butylene succinate); poly(butylene succinate-co-caproate); poly(butylene succinate-co-l-lactate); poly(butylene succinate-co-terephthalate); poly(ethylene terephthalate); poly(glycolic acid); poly(ɛ-caprolactone); poly(3-hydroxybutyrate); poly(lactic acid); poly(malic acid); oligomeric polyester; ring-opening polymerization; telechelic oligomer; thermal polycondensation

Changes in the barrier properties to gaseous H2S accompanying elongational and bending deformations imposed on silicate deposited nylon 6 films

Abstract: The changes in the barrier properties due to the damage imposed on the SiOx deposited nylon 6 films accompanying various deformations such as bending and elongation were examined by evaluating the corrosion rate of the copper plates by H2S kept in the pouches made of the damaged films. After application of elongational deformation of as high as 2% or less, only slight corrosion of the copper plates, almost similar to those of the copper plates kept in the pouches made of undeformed films, was observed. After application of elongational deformations of 3% or more, the corrosion of the copper plates was more distinct and proceeded significantly with time, Bending deformation given to the SiOx deposited nylon films also deteriorated the barrier property to H2S when the radius of curvature at the bent part was small. Comparison of the corrosion rates of the copper plates kept in the pouches made of films deformed in various ways and undeformed commercial films shows a clear relationship between the H2 permeation rate of the films and the corrosion rate of the copper plates by H2S.