bluuebunny/crossref_metadata_2025 huggingface dataset:
In‐Situ Atomic Force Microscopy Observation of Enzymatic Degradation in Poly(hydroxyalkanoic acid) Thin Films: Normal and Constrained Conditions
Authors: Kikkawa Yoshihiro , Hirota Takuya , Numata Keiji , Tsuge Takeharu , Abe Hideki , Iwata Tadahisa , Doi Yoshiharu
Published: March 2004

Summary: The enzymatic degradation of lamellar crystals in poly(hydroxyalkanoic acid) thin films has been visualized by using in‐situ dynamic force mode (tapping mode) atomic force microscopy (AFM) in buffer solution. It was found that poly(hydroxybutyric acid) (PHB) depolymerase from Ralstonia pickettii T1 degraded the thin surface layers formed at room temperature first, and that lamellar crystals formed at the crystallization temperature (110 °C) were eroded from the crystallographic a‐axis to show splintered morphologies at the tips of the crystals. In some cases, lamellar crystals were hydrolyzed from the crystallographic b‐axis, resulting in the formation of small crevices. These results suggest that disordered molecular chain‐packing regions exist in the crystal along the crystallographic a‐ and b‐axes, and that enzymatic degradation predominantly occurs from these defective regions. In addition, cantilever‐tip‐induced enzymatic degradation was carried out in the presence of PHB depolymerase. A concave area was artificially formed on the stacked lamellar crystals by the AFM tip. In‐situ AFM observation has revealed that enzymatic degradation proceeds along both the longitudinal and lateral directions of the lamellae. At the same time, the PHB depolymerase preferentially eroded the concave area along the crystallographic c‐axis. These results demonstrated that the PHB depolymerase predominantly degrades the less‐ordered molecular chain‐packing regions in the crystals.

A series of AFM images of a poly{[(R)‐3‐hydroxybutyric acid]‐co‐[8‐mol%‐(R)‐3‐hydroxyhexanoic acid]} thin film during the cantilever‐tip‐induced enzymatic degradation process.

image

A series of AFM images of a poly{[(R)‐3‐hydroxybutyric acid]‐co‐[8‐mol%‐(R)‐3‐hydroxyhexanoic acid]} thin film during the cantilever‐tip‐induced enzymatic degradation process.
Involvement of Hevea Latex Organelle Membrane Proteins in the Rubber Biosynthesis Activity and Regulatory Function
Authors: Wititsuwaannakul Dhirayos , Rattanapittayaporn Atiya , Koyama Tanetoshi , Wititsuwaannakul Rapepun
Published: March 2004

Summary: Centrifugation of fresh Hevea rubber latex yields three distinct fractions. The sediment bottom fraction (BF) content of membrane‐bound organelles is ca. 20 vol.‐% of latex. Prolonged storage or delayed use of fresh latex will result in disintegration and loss of the bottom fraction. This is due to the osmotically sensitive BF rupture and its membrane debris being tightly bound to the top rubber particles (RP) phase. The BF membrane was found to be highly active for rubber biosynthesis (RB), in contrast to previous reports that describe RB only occurring on the RP surface. It was clearly shown that washed BF membrane (WBM) was much more active than fresh RP for RB activity. WBM was highly activated by SDS for RB in a biphasic manner, but SDS strongly inhibited the RP. Probably WBM micelle formation resulted in a highly increased active surface area for RB. C55‐PP (UPP) was a very active allylic for WBM in RB function, but inactive for RP. Serial acetone extraction of WBM proteins showed a distinct profile of the fractions with different RB activity. WBM isolated proteins suspended in 2% sodium dodecyl sulfate (SDS) with an RB activity equal to that of intact WBM was with the 20% acetone protein fraction. The 60 and 80% fractions were inactive. Combining the 20 with 80% fractions showed a complete inhibition of RB activity. Complete RB loss was also found when WBM was mixed with the 80% fraction, indicating that WBM has both an enzyme system and a factor for regulation of the RB activity in a well controlled metabolic function for the latex RB process.

image
Microbial Polythioesters
Authors: Lütke‐Eversloh Tina , Steinbüchel Alexander
Published: March 2004

Summary: This feature article describes the current knowledge on biosynthesis of polythioesters (PTEs), which are exclusively accumulated by microorganisms capable to synthesize the well‐known polyhydroxyalkanoates (PHAs). Two bacterial PTE biosynthesis systems are discussed, both are depending on the cultivation conditions and appropriate feeding regimes. The first system comprises the production of PTE copolymers by Ralstonia eutropha, and the second system has been established in recombinant Escherichia coli to produce PTE homopolymers. Furthermore, synthetic PTEs and other related sulfur containing biopoylmers are briefly summarized.

General structural formula of PTEs accumulated as small granules in cells of metabolically engineered Escherichia coli.

image

General structural formula of PTEs accumulated as small granules in cells of metabolically engineered Escherichia coli.
Enzymatic Hydrolysis of α‐ and β‐Oligo(L‐aspartic acid)s by Poly(aspartic acid) Hydrolases‐1 and 2 from Sphingomonas sp. KT‐1
Authors: Hiraishi Tomohiro , Kajiyama Mariko , Yamato Ichiro , Doi Yoshiharu
Published: March 2004

Summary: The enzymatic hydrolysis of α‐ and β‐oligo(L‐aspartic acid)s by PAA hydrolase‐1 and PAA hydrolase‐2 (purified from Sphingomonas sp. KT‐1) was performed to elucidate the mechanism of the microbial degradation by Sphingomonas sp. KT‐1 of the thermally synthesized α,β‐poly(D,L‐aspartic acid) (tPAA). GPC analysis of the hydrolyzed products of α‐ and β‐tetra(L‐aspartic acid)s by PAA hydrolase‐1 has showed that PAA hydrolase‐1 is capable of hydrolyzing only the specific amide bonds between β‐aspartic acid units. The RP‐HPLC analysis of the enzymatic hydrolysis of β‐oligo(L‐aspartic acid)s (4 and 5 mers) by PAA hydrolase‐1 has suggested that the enzymatic hydrolysis of β‐oligo(L‐aspartic acid)s occurs via an endo‐mode cleavage. In contrast, PAA hydrolase‐2 hydrolyzed both α‐ and β‐oligo(L‐aspartic acid)s via an exo‐mode cleavage to yield L‐aspartic acid as a final product. A kinetic study on the enzymatic hydrolysis of α‐oligo(L‐aspartic acid)s (3 to 7 mers) by PAA hydrolase‐2 has indicated that Km values are almost independent of the number of monomer units in oligomers of 4 to 7 mers, while that Vmax values are markedly dependent on the chain length and show a maximum value at 5 mer.

A proposed mechanism of the enzymatic hydrolysis of tPAA by PAA hydrolase‐1 and PAA hydrolase‐2 in the cell of Sphingomonas sp. KT‐1.

image

A proposed mechanism of the enzymatic hydrolysis of tPAA by PAA hydrolase‐1 and PAA hydrolase‐2 in the cell of Sphingomonas sp. KT‐1.
Crystal Structure, Thermal Behavior and Enzymatic Degradation of Poly(tetramethylene adipate) Solution‐Grown Chain‐Folded Lamellar Crystals
Authors: Iwata Tadahisa , Kobayashi Shiomi , Tabata Kenji , Yonezawa Noriyuki , Doi Yoshiharu
Published: March 2004

Summary: Solution‐grown chain‐folded lamellar single crystals of poly(tetramethylene adipate) (PTMA) were prepared from a dilute solution of 2‐methyl‐1‐propanol by isothermal crystallization. PTMA crystals were hexagonal‐shaped and polyethylene decoration of the crystals resulted in a “six cross‐sector” surface morphology and showed that the average direction of chain folding is parallel to the crystal growth planes of {110} and {010}. Chain‐folded lamellar crystals gave well‐resolved electron diffraction diagrams corresponding to all the equatorial reflections of the X‐ray fiber diagram obtained from stretched PTMA melt‐quenched film (β structure). The unit cell parameters of the β structure of PTMA were determined as a = 0.503 nm, b = 0.732 nm and c (fiber axis) = 1.442 nm with an orthorhombic crystal system. The fiber repeat distance is appropriate for an all‐trans backbone conformation for the straight stems. The setting angle, with respect to the a axis, is ±46° for the corner and center chains. Thermal behavior of lamellar crystals has been investigated by means of transmission electron microscopy (TEM) and atomic force microscopy (AFM). The lamellar thickness at the edges of the crystal increased after thermal treatment with taking the molecular chains into recrystallization parts; the holes then opened up at the thickening front of the crystal. The morphological changes of lamellar crystals after enzymatic degradation by Lipase type XIII from Pseudomonas sp. and water‐soluble products were characterized by TEM, AFM, gel permeation chromatography, high performance liquid chromatography and fast atom bombardment mass spectrometry. The degradation progressed mainly from the edges of the lamellar crystals without decreasing the molecular weights and the lamellar thicknesses. The central portion of single crystals was often degraded by enzymatic attacks. This result combined with thermal behavior indicates that the loosely chain‐packing region exists inside the single crystal, and that molecular chains in this region have higher mobility against thermal and enzymatic treatments.

PTMA hexagonal‐shaped single crystal TEM micrograph.

image

PTMA hexagonal‐shaped single crystal TEM micrograph.
Lactic Acid‐Based Functionalized Polymers via Copolymerization and Chemical Modification
Authors: Saulnier Benjamin , Ponsart Stephanie , Coudane Jean , Garreau Henry , Vert Michel
Published: March 2004

Summary: Poly(lactic acid) polymers (PLA) are presently the most attractive compounds in the field of artificial degradable and biodegradable polymers. In order to enlarge the family, and thus the range of accessible properties, stereocopolymers and copolymers with various co‐monomers have been synthesized. However, very few are functionalized, i.e. include functional groups attached to the main chains or as part of the side chains. In the search for degradable PLA‐type polymers bearing functional groups to serve as intermediates for further chemical modifications, we are exploring two different routes. The first one is copolymerization with a protected hydroxyl‐bearing lactide‐type monomer, namely 3‐(1,2,3,4‐tetraoxobutyldiisopropylidene)dioxane‐2,5‐dione. The second route consists of the formation of a carbanionic site in the α‐position to intrachain carbonyl functions by using lithium N,N‐diisopropylamide followed by the coupling of electrophiles. Recent advances in this search are presented using several examples. In particular, it is shown that OH‐functionalized PLA‐type macromolecules can be made fluorescent by chemical coupling. It is also shown that substituents can be attached to PLA‐type macromolecules in solution or to the surface of PLA‐based devices selectively.

Example of chemical modifications of hydroxyl‐bearing PLA‐type polymers derived from gluconic and glycolic acids (via gluconolactone) and lactic acid (via lactide).

image

Example of chemical modifications of hydroxyl‐bearing PLA‐type polymers derived from gluconic and glycolic acids (via gluconolactone) and lactic acid (via lactide).
Synthesis and Properties of Graft Copolymers Based on Poly(3‐hydroxybutyrate) Macromonomers
Authors: Nguyen Sophie , Marchessault Robert H.
Published: March 2004

Summary: Graft copolymers of poly(methyl methacrylate) with poly(3‐hydroxybutyrate), PHB, segments as long side chains were prepared by the macromonomer method. PHB macromonomers were prepared from the esterification of oligomers with 2‐hydroxyethyl methacrylate at their carboxylic acid end. Esterification products displayed low polydispersity indices (ca. 1.2) and a functionality of over 83%, with a $\overline M _{\rm n}$ of 2 020. Using free radical polymerization methods, the macromonomers were copolymerized with methyl methacrylate to yield graft (comb type) copolymers at different comonomer feed ratios. The graft copolymers contained from 0.5 to 14 mol‐% of PHB blocks, with a glass transition temperature decreasing from 100 to 3 °C.

Synthesis of PMMA‐graft‐PHB by the copolymerization of PHB macromonomers with methyl methacrylate.

image

Synthesis of PMMA‐graft‐PHB by the copolymerization of PHB macromonomers with methyl methacrylate.
Metabolic Engineering for the Production of Copolyesters Consisting of 3‐Hydroxybutyrate and 3‐Hydroxyhexanoate by Aeromonas hydrophila
Authors: Qiu Yuan‐Zheng , Ouyang Shao‐Ping , Shen Zhongyao , Wu Qiong , Chen Guo‐Qiang
Published: March 2004

Summary: Aeromonas hydrophila 4AK4 was able to synthesize copolyesters consisting of 3‐hydroxybutyrate (3HB) and about 15 mol‐% 3‐hydroxyhexanoate (3HHx) (PHBHHx) when grown in long chain fatty acids such as dodecanoate regardless of growth conditions. To regulate the unit fraction in PHBHHx, phbA and phbB genes encoding β‐ketothiolase and acetoacetyl‐CoA reductase in Ralstonia eutropha, were introduced into A. hydrophila 4AK4. When gluconate was used as cosubstrate of dodecanoate, the recombinant produced PHBHHx containing 3–12 mol‐% 3HHx, depending on the gluconate concentration in media. Vitreoscilla hemoglobin gene, vgb, was also introduced into the above recombinant, resulting in improved PHBHHx content from 38 to 48 wt.‐% in shake flask study. Fermentor studies also showed that increased gluconate concentration in medium containing dodecanoate promoted the recombinant strain harboring phbA and phbB genes to incorporate more 3HB unit into PHBHHx, resulting in reduced 3HHx fraction. Recombinant A. hydrophila harboring phbA, phbB and vgb genes demonstrated better PHBHHx productivity and higher conversion efficiency from dodecanoate to PHBHHx than those of the recombinant without vgb in fermentation study. Combined with the robust growth property and simple growth requirement, A. hydrophila 4AK4 appeared to be a useful organism for metabolic engineering.

Metabolic pathways of PHBHHx biosynthesis in recombinant A. hydrophila 4AK4 (pTG01) from cosubstrates.

image

Metabolic pathways of PHBHHx biosynthesis in recombinant A. hydrophila 4AK4 (pTG01) from cosubstrates.
Polymer Alloys of Nodax Copolymers and Poly(lactic acid)
Authors: Noda Isao , Satkowski Michael M. , Dowrey Anthony E. , Marcott Curtis
Published: March 2004

Summary: Properties of polymer alloys comprising poly(lactic acid) and Nodax copolymers are investigated. Nodax is a family of bacterially produced polyhydroxyalkanoate (PHA) copolymers comprising 3‐hydroxybutyrate (3HB) and other 3‐hydroxyalkanoate (3HA) units with side groups greater than or equal to three carbon units. The incorporation of 3HA units with medium‐chain‐length (mcl) side groups effectively lowers the crystallinity and the melt temperature, Tm, of this class of PHA copolymers, in a manner similar to that of alpha olefins controlling the properties of linear low density polyethylene. The lower Tm makes the material easier to process, as the thermal decomposition temperature of PHAs is then relatively low. The reduced crystallinity provides the ductility and toughness required for many plastics applications. When a small amount of ductile PHA is blended with poly(lactic acid) (PLA), a new type of polymer alloy with much improved properties is created. The toughness of PLA is substantially increased without a reduction in the optical clarity of the blend. The synergy between the two materials, both produced from renewable resources, is attributed to the retardation of crystallization of PHA copolymers finely dispersed in a PLA matrix as discrete domains.

Effect of the particle size on the overall crystallization rate by low spontaneous nucleation frequency.

image

Effect of the particle size on the overall crystallization rate by low spontaneous nucleation frequency.
Lipase‐Catalyzed Transformation of Poly(lactic acid) into Cyclic Oligomers
Authors: Takahashi Yosuke , Okajima Sachiko , Toshima Kazunobu , Matsumura Shuichi
Published: March 2004

Summary: Enzymatic transformations into cyclic oligomers were carried out with the objective of developing chemical recycling of poly(lactic acid)s, such as poly(D,L‐lactic acid) (PDLLA), poly(D‐lactic acid) (PDLA) and poly(L‐lactic acid) (PLLA), which are typical biodegradable polymers. They were degraded by lipase in an organic solvent to produce the corresponding cyclic oligomer with a molecular weight of several hundreds. PDLLA (with a $\overline M _{\rm w}$ of 84 000) was quantitatively transformed into cyclic oligomers by lipase RM (Lipozyme RM IM) in chloroform/hexane at 60 °C. PLLA (with a $\overline M _{\rm w}$ of 120 000) was transformed into cyclic oligomer by lipase CA (Novozym 435) at a higher temperature of 100 °C in o‐xylene. The oligomer structure was identified by 1H and 13C NMR spectroscopy and MALDI‐TOF (matrix assisted laser desorption/ionization‐time‐of‐flight) mass spectrometry.

Enzymatic transformations into cyclic oligomers with the objective of developing chemical recycling of poly(lactic acid)s.

image

Enzymatic transformations into cyclic oligomers with the objective of developing chemical recycling of poly(lactic acid)s.
Organic‐Inorganic Hybrids from Renewable Plant Oils and Clay
Authors: Uyama Hiroshi , Kuwabara Mai , Tsujimoto Takashi , Nakano Mitsuru , Usuki Arimitsu , Kobayashi Shiro
Published: March 2004

Summary: This study deals with the preparation and properties of a new class of organic‐inorganic hybrids from renewable resources. The hybrids were synthesized by an acid‐catalyzed curing of epoxidized triglycerides in the presence of an organophilic montmorillonite (a modified clay). The mechanical properties were improved by the incorporation of clay in the oil‐based polymer matrix. The reinforcement effect due to the addition of clay was confirmed by dynamic viscoelasticity analysis. The hybrids showed relatively high thermal stability. The co‐curing of epoxidized soybean and linseed oils in the presence of clay produced hybrids with controlled mechanical and coating properties. The barrier property of the hybrid towards water vapor was superior to that of the oil polymer. The development of the present hybrids consisting of inexpensive renewable resources, triglyceride and clay is expected to contribute to global sustainability.

TEM image of the ESOC18‐Mont hybrid with a clay content of 10%.

image

TEM image of the ESOC18‐Mont hybrid with a clay content of 10%.
Hydrogel Formation between Enantiomeric B‐A‐B‐Type Block Copolymers of Polylactides (PLLA or PDLA: A) and Polyoxyethylene (PEG: B); PEG‐PLLA‐PEG and PEG‐PDLA‐PEG
Authors: Mukose Takashi , Fujiwara Tomoko , Nakano Junko , Taniguchi Ikuo , Miyamoto Masatoshi , Kimura Yoshiharu , Teraoka Iwao , Woo Lee Chan
Published: March 2004

Summary: A mixed suspension of the enantiomeric B‐A‐B triblock copolymers, polyoxyethylene‐block‐poly(L‐lactide)‐block‐polyoxyethylene (PEG‐PLLA‐PEG) and polyoxyethylene‐block‐poly(D‐lactide)‐block‐polyoxyethylene (PEG‐PDLA‐PEG), was found to induce reversible gel‐to‐sol transition depending on the polymer concentration and temperature. The storage and loss moduli of the gel formed at lower temperature were much higher than those of the gel prepared from the corresponding ABA‐type triblock copolymers because of the higher polymer concentration in the former. Although the stereo‐complexation of the PLLA and PDLA blocks occurred at higher temperature also in the B‐A‐B copolymers, it was not responsible for the gelation of the mixed suspension. The PEG chains, involved in the helix formation of the PLLA and PDLA, should form helices with opposite helical senses to aggregate and lead the gelation of the system.

Phase changes of the single dispersion of PLLA‐PEG at 37 °C (a) and 75 °C (b) and the mixed dispersion of PLLA‐PEG and PDLA‐PEG at 37 °C (c) and (d) 75 °C (d).

image

Phase changes of the single dispersion of PLLA‐PEG at 37 °C (a) and 75 °C (b) and the mixed dispersion of PLLA‐PEG and PDLA‐PEG at 37 °C (c) and (d) 75 °C (d).
Biodegradable Polyesters Reinforced with Surface‐Modified Vegetable Fibers
Authors: Zini Elisa , Baiardo Massimo , Armelao Lidia , Scandola Mariastella
Published: March 2004

Summary: Flax fibers are investigated as reinforcing agents for biodegradable polyesters (Bionolle and poly(lactic acid) plasticized with 15 wt.‐% of acetyltributyl citrate, p‐PLLA). The composites are obtained either by high temperature compression molding fiber mats sandwiched between polymer films, or by batch mixing fibers with the molten polymer. Fibers in composites obtained by the latter method are much shorter (140–200 μm) than those of the mats (5 000 μm). Flax fibers are found to reinforce both p‐PLLA and Bionolle (i.e. tensile modulus and strength increase) when composites based on fiber mats are investigated. Conversely, analogous composites obtained by batch mixing show poor mechanical properties. The observed behavior is attributed to the combined effect of fiber length and fiber‐matrix adhesion. If flax fibers with a modified surface chemistry are used, the strength of short fiber composites is seen to improve significantly because the interface strengthens and load is more efficiently transferred. Appropriate surface modifications are performed by heterogeneous acylation reactions or by grafting poly(ethylene glycol) chains (PEG, molecular weight 350 and 750). The highest tensile strength of p‐PLLA composites is reached when PEG‐grafted flax fibers are used, whereas in the case of Bionolle the best performance is observed with acylated fibers.

SEM micrograph of the fracture surface (from side to side) of a freeze fractured composite sheet of A‐p‐PLLA with A2 fibers.

image

SEM micrograph of the fracture surface (from side to side) of a freeze fractured composite sheet of A‐p‐PLLA with A2 fibers.
Mass Spectrometry Feedback Control for Synthesis of Polyhydroxyalkanoate Granule Microstructures in Ralstonia eutropha
Authors: Pederson Erik N. , Srienc Friedrich
Published: March 2004

Summary: Polyhydroxyalkanoate (PHA) granules with core‐shell layered microstructure were synthesized in Ralstonia eutropha using periodic feeding of valeric acid into a growth medium containing excess fructose. The O2 consumption and CO2 evolution rates, determined by off‐gas mass spectrometry, have been used as sensitive measures to indicate the type of nutrients utilized by R. eutropha during PHA synthesis. Domains of poly‐3‐hydroxybutyrate (PHB) were formed during polymer storage conditions when only fructose was present. Feeding of valeric acid (pentanoic acid) resulted in the synthesis of hydroxyvalerate (HV) monomers, forming a poly‐3‐hydroxybutyrate‐co‐valerate (PHBV) copolymer. The synthesis of desired polymer microstructures was monitored and controlled using online mass spectrometry (MS). The respiratory quotient (RQ) was unique to the type of polymer being synthesized due to increased O2 consumption during PHBV synthesis. MS data was used as the control signal for nutrient feeding strategies in the bioreactor. The core‐shell structures synthesized were verified in cells using transmission electron microscopy after thin sectioning and staining with RuO4. It was demonstrated that the synthesis of core‐shell microstructures can be precisely controlled utilizing a MS feedback control system.

Monitoring of R. eutropha growth and PHA synthesis in a batch reactor (oxygen uptake rate: OUR; carbon dioxide evolution rate: CER; respiratory quotient: RQ).

image

Monitoring of R. eutropha growth and PHA synthesis in a batch reactor (oxygen uptake rate: OUR; carbon dioxide evolution rate: CER; respiratory quotient: RQ).
High Temperature Bulk Reaction between Poly(ethylene terephtalate) and Lactones: 1H NMR and SEC/MALDI‐TOF MS Study
Authors: Tillier Delphine , Lefebvre Hervé , Tessier Martine , Blais Jean‐Claude , Fradet Alain
Published: March 2004

Summary: Copolyesters containing aliphatic units in the main chain were obtained by reacting high molar mass poly(ethylene terephthalate) (PET) with ε‐caprolactone or δ‐valerolactone at high temperature in the bulk. γ‐Butyrolactone did not react in these conditions. Thermal properties were studied by DSC and TGA, and structural characterizations were carried out by 1H NMR spectroscopy and SEC/MALDI‐TOF mass spectrometry off‐line coupling. These techniques demonstrate the insertion of lactone units in PET chains. Linear species with hydroxy, carboxy and vinyl ester end‐groups were clearly identified in the mass spectra, together with cyclic copolymer species. Narrow‐distribution copolyester SEC fractions were characterized by MALDI‐TOF mass spectrometry and used to establish a SEC calibration curve against absolute molar masses. The results indicate that the conventional polystyrene SEC calibration strongly overestimates copolyester molar masses. The degree of randomness of these copolyesters, determined by 1H NMR, shows that chain microstructure presents some block‐copolymer character. The thermal properties of the copolyesters are also discussed.

Reaction between PET and γ‐butyrolactone (x = 3), δ‐valerolactone (x = 4), or ε‐caprolactone (x = 5).

magnified image

Reaction between PET and γ‐butyrolactone (x = 3), δ‐valerolactone (x = 4), or ε‐caprolactone (x = 5).
Crystallization and Melting Behavior of Poly(3‐hydroxybutyrate)‐Based Blends
Authors: Chan Chin Han , Kummerlöwe Claudia , Kammer Hans‐Werner
Published: March 2004

Summary: Blends of high molecular weight poly(R‐3‐hydroxybutyrate) (PHB) ($\overline M _{\rm w}$ = 352 000 g · mol−1), comprising of either low molecular weight poly(R‐3‐hydroxybutyrate) (D‐PHB) ($\overline M _{\rm w}$ = 3 900 g · mol−1) or poly[(R‐3‐hydroxybutyrate)‐co‐(R‐3‐hydroxyvalerate)] (PHBV) ($\overline M _{\rm w}$ = 238 000 g · mol−1) with 12 mol‐% hydroxyvalerate (HV) content as a second constituent, were investigated along with the thermal properties and morphologies. After isothermal crystallization, a lowering of the melting temperature of PHB can be observed with increasing content of the second component in the blends. This behavior points towards miscibility of the constituents both in the liquid and the solid state. Crystallization kinetics was studied under isothermal and non‐isothermal conditions. The overall kinetics of isothermal crystallization was analyzed in terms of the Avrami equation. Only one crystallization peak is observed in all cases for the PHB/D‐PHB and PHB/PHBV blends under the conditions studied. This demonstrates co‐crystallization of the constituents. The addition of D‐PHB or PHBV to PHB reduces the rate of crystallization of the blends compared to that of neat PHB. The corresponding activation energies of crystallization also decrease with an increasing concentration of the second constituent. Non‐isothermal crystallization, carried out with different cooling rates held constant, is discussed in terms of a quasi‐isothermal approach. The corresponding rate constants as functions of reciprocal undercooling show Arrhenius‐like behavior in a certain range of temperatures. At sufficiently high undercooling, the rate constants of crystallization for the isothermal process exceed those reflecting non‐isothermal conditions, whereas in the limit of low undercoolings, the rate constants become similar. Ring‐banded morphologies are observed when PHB is in excess. When the respective second component is the major component, fibrous textures of the spherulites develop.

Polarized micrograph of PHB/PHBV 90/10.

magnified image

Polarized micrograph of PHB/PHBV 90/10.
Stable Free‐Radical Copolymerization of Styrene with Acrylates Using OH‐TEMPO
Authors: Appelt Mathias , Schmidt‐Naake Gudrun
Published: March 2004

Summary: Stable free‐radical copolymerizations (SFRP) of styrene with N‐acryloyl morpholine (AMo), 2‐ethoxyethyl acrylate (EOEA) and isobornyl acrylate (iBoA), respectively, were carried out under control of the stable nitroxide radical 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐N‐oxyl (OH‐TEMPO). The polymerizations were initiated by a polystyrene macroinitiator (PS‐MI). No accelerating agents were used. In contrast to the experiences made with methacrylates there was no decrease in the polymerization rates up to 50 mol‐% of AMo or EOEA in the monomer mixture. This behavior was ascribed to a compensation of the lack of thermal initiation by the high propagation rate constants of the acrylates. The produced AB diblock polymers were successfully employed in block extension reactions in styrene yielding ABA triblock polymers. Copolymerization reactivity ratios (r‐values) and glass transition temperatures have been estimated.

Monomer structures.

magnified image

Monomer structures.
Synthesis of Norbornene Derivatives by Diels‐Alder Cycloaddition and Subsequent Copolymerization with Maleic Anhydride
Authors: Pasquale Anthony J. , Fornof Ann R. , Long Timothy E.
Published: March 2004

Summary: Several norbornene (Nb) derivatives were synthesized by facile Diels‐Alder cycloaddition reactions of cyclopentadiene with α‐olefins containing electron‐withdrawing groups such as nitrile (CN), phosphonate, and ester. The Diels‐Alder adducts were subsequently copolymerized with maleic anhydride (MAH) using free radical polymerization conditions previously determined for MAH/Nb copolymerizations. Further functionality was introduced into the copolymers through acid‐catalyzed hydrolysis of poly(Nb‐alt‐MAH) and poly(NbCN‐alt‐MAH) copolymers. FTIR confirmed hydrolysis of the anhydrides to carboxylic acid‐functionalities and indicated no appreciable hydrolysis of the nitrile functionality. Observed copolymerization rates (kobs) were measured using in situ FTIR. A dramatic decrease in the rate of copolymerization was observed for the Nb derivatives that contained a strong electron‐withdrawing functionality. This observation suggested a significant electronic influence on the free radical copolymerization rate with maleic anhydride due to the electron‐withdrawing nature of the Nb substituents.

Vinylene region of in situ FTIR “waterfall” plot for 50/50 Nb/MAH alternating copolymerization.

magnified image

Vinylene region of in situ FTIR “waterfall” plot for 50/50 Nb/MAH alternating copolymerization.
Synthesis and ATRP Activity of New TREN‐Based Ligands
Authors: Gromada Jérôme , Spanswick James , Matyjaszewski Krzysztof
Published: March 2004

Summary: Ligands suitable for atom transfer radical polymerization (ATRP) were prepared by the Michael addition of several acrylates (allyl, benzyl, butyl, 2‐ethylhexyl, and 3‐(dimethoxymethylsilyl)propyl acrylates) with tris(2‐aminoethyl)amine (TREN). These ligands, readily prepared from inexpensive precursors, were used for the preparation of catalyst complexes suitable for polymerization of (meth)acrylates and styrene, providing activity comparable to catalysts currently used for these monomers. Catalysts containing ligands with a dimethoxymethylsilyl substituent were examined for copper removal after the reaction mixture was contacted with silica gel.

magnified image
Synthesis of Structurally‐Controlled AIDS Vaccine Model with Glyco‐Peptide Dendrimer Scaffolds
Authors: Baigude Huricha , Katsuraya Kaname , Okuyama Kohsaku , Uryu Toshiyuki
Published: March 2004

Summary: A novel glyco‐peptide dendrimer‐type AIDS vaccine model with a well‐defined structure was synthesized. A low‐substituted, monodispersed, glyco‐peptide dendrimer was prepared by binding maltose to a proline‐poly(lysine) dendrimer with monofunctional prolyl amino groups on the periphery. To the hemispherical maltose‐proline‐poly(lysine) dendrimer, succinic anhydride was reacted to provide succinylated dendrimer with an average of 13 succinyl carboxyl groups per dendrimer. The reactivity of succinyl‐maltose‐proline‐poly(lysine) dendrimer was investigated by coupling a tripeptide to the carboxyl group in water using 1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide hydrochloride (EDC) as a condensing agent. By binding two kinds of peptide sequences included in the envelope glycoprotein of HIV to the dendrimer, AIDS vaccine models with glyco‐peptide dendrimer scaffold were synthesized. The structure of the vaccine models was determined by NMR and MALDI‐TOF mass analyses.

Leu‐Pro‐Gly‐succinyl‐maltose‐proline‐poly(lysine) dendrimer generation 3.

magnified image

Leu‐Pro‐Gly‐succinyl‐maltose‐proline‐poly(lysine) dendrimer generation 3.
Atom Transfer Radical Polymerization Using Multidentate Amine Ligands Supported on Soluble Hyperbranched Polyglycidol
Authors: Kumar Kainthan Rajesh , Kizhakkedathu Jayachandran N. , Brooks Donald E.
Published: March 2004

Summary: Controlled polymerization of styrene in toluene was achieved by atom transfer radical polymerization (ATRP) using hyperbranched polyglycidol‐supported multidentate amine ligands/CuIBr catalyst systems. These catalyst systems with nanoscopic dimensions were more active than the corresponding low‐molecular‐weight ligands. The controlled/living nature of the polymerization is supported by linear first order plots (ln[M]o/[M] versus time) and a linear increase of $\overline M _{\rm n}$ versus conversion as well as low polydispersity. Similar controlled polymerization of methyl methacrylate was possible in acetonitrile. Up to 97% of total copper used for polymerization could be removed from the polymer by simple precipitation in methanol and filtration.

Molecular weight characteristics for styrene polymerization using PG‐triamine as a ligand.

magnified image

Molecular weight characteristics for styrene polymerization using PG‐triamine as a ligand.
Synthesis of a New Macromonomer from 2‐(Dimethylamino)ethyl Methacrylate Bearing 1‐(Isopropenylphenyl)‐1,1‐dimethylmethyl Isocyanate Group
Authors: Boyer Cyril , Boutevin Gilles , Robin Jean‐Jacques , Boutevin Bernard
Published: March 2004

Summary: The telomerization of 2‐(dimethylamino)ethyl methacrylate (DMAEMA) with 2‐mercaptoethanol in acetonitrile shows that the telogen can react with the monomer by nucleophilic addition. It is to say that the tertiary amino group leads to nucleophilic addition rather than telomerization. The oligomers thus obtained were functionalized with 1‐(isopropenylphenyl)‐1,1‐dimethylmethyl isocyanate (TMI) in anhydrous toluene to afford macromonomers. These macromonomers were copolymerized with styrene and the r1, r2 ratio was determined according to Jaacks and Macret's methods. It was thereby demonstrated that the r1 value for this type of monomer is close to zero.

Structure of the model molecule.

magnified image

Structure of the model molecule.
A Model System for the Thermodynamic Analysis of Reaction‐Induced Phase Separation: Solutions of Polystyrene in Bifunctional Epoxy/Amine Monomers
Authors: Zucchi Ileana A. , Galante María J. , Borrajo Julio , Williams Roberto J. J.
Published: March 2004

Summary: A model system, consisting of a linear polymer dissolved in a bifunctional monomer/co‐monomer solvent, was selected to test the applicability of the Flory‐Huggins (FH) theory in the absence of the usual assumptions present in the analysis of modified thermosetting polymers. Solutions of two almost monodisperse polystyrenes (PS, $\overline M _{\rm n}$ = 83 000 or 217 000), in diglycidyl ether of bisphenol A (DGEBA) and in stoichiometric DGEBA/BA (benzylamine) solutions, exhibited an upper critical solution temperature (UCST) behavior. Cloud‐point curves (CPC) were fitted with the FH model using an interaction parameter depending on both temperature and concentration, χ = (a + b/T)/(1 − cϕ2), where ϕ2 represents the volume fraction of PS. A group‐contribution method provided a reasonable explanation of the observed trends. Cloud‐point times in the course of the DGEBA/BA stepwise polymerization, carried out at 70 °C and 80 °C, were determined for solutions containing 2.5 to 15 wt.‐% PS ($\overline M _{\rm n}$ = 83 000). Times were transformed to conversions using kinetic curves determined by Fourier Transform Infrared Spectroscopy (FT‐IR) and Size Exclusion Chromatography (SEC). The analysis of cloud‐point conversions with the FH model was performed considering the (ideal) distribution of epoxy/amine species generated as a function of conversion. An empirical fitting of cloud‐point curves was possible with the use of an interaction parameter decreasing with conversion. Possibilities of improving the thermodynamic description of a polymerization‐induced phase separation are discussed.

Cloud‐point curves for PS‐DGEBA binary solutions.

magnified image

Cloud‐point curves for PS‐DGEBA binary solutions.
Solid Polymer Electrolytes, 9
Authors: Liang Wuu‐Jyh , Kao Hsien‐Ming , Kuo Ping‐Lin
Published: March 2004

Summary: A new hybrid polymer electrolyte system containing polysiloxane and polyether segments has been designed and prepared by epoxide crosslinking. The thermal behavior, structure and ionic conductivity of the hybrid materials were investigated and characterized by differential scanning calorimetry (DSC), 13C solid‐state NMR spectroscopy and alternating current (AC) impedance measurements. Two glass transition temperatures were observed, showing a dependence on the composition and LiClO4/PC content. The miscibility of the polymer components in the hybrid was studied by examining the 1H spin relaxation times in the laboratory frame (T1(H)) and in the rotating frame (T1ρ(H)) with various compositions. Multi‐relaxation T1ρ(H) behavior has been observed, indicative of the presence of structural heterogeneity on the timescale of T1ρ(H). These results are correlated and used to interpret the phenomenon of the conductivity of the lithium ion in the matrix of hybrid networks.

Schematic structure of polysiloxane/polyether networks.

magnified image

Schematic structure of polysiloxane/polyether networks.
Retarded Anionic Polymerization: Copolymerization of Butadiene and Styrene in the Presence of Alkyllithium and n,s‐Dibutylmagnesium or Triisobutylaluminium Derivatives
Authors: Carlotti Stéphane , Ménoret Stéphane , Barabanova Anna , Desbois Philippe , Deffieux Alain
Published: March 2004

Summary: The influence of Lewis acid additives on the anionic butadiene polymerization using lithium as a counter ion in non‐polar solvent is investigated. A decrease of the polymerization rate was always observed. In the presence of n,s‐Bu2Mg the percentage of 1,2‐vinyl units increases with the [Mg]/[Li] ratio. This evolution can be explained by further complexation of lithium with free dialkylmagnesium modifying the nature of the propagating species and/or possible 1,4 to 1,2 isomerization during chain exchanges between lithium and magnesium derivatives. As a result of the transmetallation process, 0.5 to 1 supplementary chains are formed by magnesium depending on the [Mg]/[Li] ratio. In contrast, the iBu3Al/RLi system does not yield any modification of polybutadiene microstructure, which remains close to the one observed with s‐BuLi alone. The determination of the reactivity ratios in styrene‐butadiene copolymerization shows that tapered‐like copolymers are obtained in the presence of both n,s‐Bu2Mg and iBu3Al. However the magnesium derivative induces a lesser increase of styrene incorporation in the copolymer than the aluminium additive. The observed microstructure and reactivity ratios support that the monomer insertion proceeds directly into heterocomplexes.

magnified image
Non‐Isothermal Crystallization of Poly(trimethylene terephthalate) (PTT)/Clay Nanocomposites
Authors: Hu Xianbo , Lesser Alan J.
Published: March 2004

Summary: The non‐isothermal crystallization of intercalated poly(trimethylene terephthalate) (PTT)/clay nanocomposites was investigated quantitatively by different methods. Non‐isothermal crystallization of pure PTT can be described by the Ozawa equation, but the Ozawa theory is not valid for PTT/clay nanocomposites. The addition of clay into PTT decreases the crystallization half‐time while increasing the crystallinity and crystallization rate. The PTT/modified clay nanocomposites, in turn, have a higher crystallization rate parameter, k1/n, and a lower crystallization half‐time compared to unmodified clay/PTT composites. The crystallization activation energy, calculated from Kissinger equation, of PTT, PTT/unmodified clay, and PTT/modified clay composites are 100, 180, and 198–230 kJ · mol−1, respectively. Similarly, the nucleating activities of the unmodified clay and modified clays are 0.73 and 0.51–0.58, respectively. Although the addition of clay increases the crystallization activation energy, the clay still acts as an effective nucleating agent and increases the crystallization rate and crystallinity of PTT. Further, the modified nanoscale clays are more effective nucleating agents than the unmodified counterparts, and the most effective nucleating concentration of nano‐clay is between 1.0–3.0 wt.‐%.

The crystallization half‐time, t1/2, decreases as a function of cooling rate, Q, and decreases with an increase in clay concentration.

magnified image

The crystallization half‐time, t1/2, decreases as a function of cooling rate, Q, and decreases with an increase in clay concentration.
Cholesteric Liquid‐Crystalline Side‐on Polysiloxanes: Effects of Biaxiality on the Cholesteric Structure
Authors: Ogawa Hiroshi , Stibal‐Fischer Elke , Finkelmann Heino
Published: March 2004

Summary: Biaxial side‐on cholesteric copolysiloxanes with laterally attached mesogenic groups were investigated in mixtures with a low molar mass liquid crystal. While mixtures with a low concentration of the polymer exhibit the conventional fingerprint texture, for concentrations above about 60 mol‐% characteristic irregularities appear in the cholesteric structure that are obviously due to phase biaxiality. Besides the absence of pseudo‐isotropic lines, irregular patterns perpendicular to the helix axis emerge and the periodic distance of regions with similar optical properties along the helix axis is strongly disturbed. This suggests that the photonic band gap width of a uniaxial cholesteric phase becomes strongly affected when a phase transformation into a biaxial cholesteric phase occurs.

Cholesteric fingerprint texture of a mixture of uniaxial nematic monomer and biaxial cholesteric polymer.

magnified image

Cholesteric fingerprint texture of a mixture of uniaxial nematic monomer and biaxial cholesteric polymer.
Golden‐age gambling: Psychological benefits and self‐concept dynamics in aging consumers' consumption experiences
Authors: Loroz Peggy Sue
Published: March 2004

Phenomenological investigation of casino gambling among older consumers yields the identification of the psychological benefits of this consumption experience for this population. Control, Lift, and Escape emerge as central themes as older consumers' gambling experiences unfold, and the elements and psychological outcomes of each of these themes are discussed. Through interpretive analysis, a conceptual framework is developed in which these factors serve an intermediary role between the more shallow hedonic responses of “fantasies, feelings, and fun” (Holbrook & Hirschman, 1982) and deeper aspects of the self. It is proposed that the psychological benefits of gambling and other forms of experiential consumption may ultimately reinforce and enhance seniors' self‐concepts. © 2004 Wiley Periodicals, Inc.
Hope, hopelessness, and coping: A framework for class‐distinctive cognitive capital
Authors: Henry Paul
Published: March 2004

Evidence that a variety of psychological dispositions vary systematically with social class has been reported in the marketing literature over the last 50 years. However, recent work has been extremely limited. Research progress has been stifled because of poor conceptual specification and lack of an integrative framework capable of grounding these dispositions in theory. This article draws upon the psychology of coping—specifically harnessing hope/hopelessness theories—to develop a much‐needed framework. This will facilitate clear conceptual specification of the psychological dispositions where social class distinctions have been proposed, and specify the relations between each of the dispositions. The term cognitive capital is introduced to capture the idea that one's mix of psychological dispositions operates as a system that can be thought of as an important type of resource that is gradationally distributed with social class level. This cognitive‐capital system impacts life chances and quality‐of‐life outcomes via the predominant pattern of coping responses that are employed in dealing with the many adversities, threats, and challenges that life typically presents. The framework provides academics with a vehicle to progress understanding of these psychological phenomena, marketing communicators with an enriched picture of class‐based distinctions, and public policy makers with an understanding of levers that contribute to social inequality. © 2004 Wiley Periodicals, Inc.
Plasma‐Initiated Controlled/Living Radical Polymerization of Methyl Methacrylate in the Presence of 2‐Cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN)
Authors: Chen Gaojian , Zhu Xiulin , Zhu Jian , Cheng Zhenping
Published: March 2004

Summary: Plasma‐initiated controlled/living radical polymerization of methyl methacrylate (MMA) was carried out in the presence of 2‐cyanoprop‐2‐yl 1‐dithionaphthalate. Well‐defined poly(methyl methacrylate) (PMMA), with a narrow polydispersity, could be synthesized. The polymerization is proposed to occur via a RAFT mechanism. Chain‐extension reactions were also successfully carried out to obtain higher molecular weight PMMA and PMMA‐block‐PSt copolymer.

Dependence of ln([M]0/[M]) on post‐polymerization time (above), and \overline M _{\rm n} and PDI against conversion (below) for plasma initiated RAFT polymerization of MMA at 25 °C.

magnified image

Dependence of ln([M]0/[M]) on post‐polymerization time (above), and \overline M _{\rm n} and PDI against conversion (below) for plasma initiated RAFT polymerization of MMA at 25 °C.
New Method of Synthesis of Poly(ester amide)s Derived from the Incorporation of Glycolic Acid Residues into Aliphatic Polyamides
Authors: Vera Montserrat , Rodríguez‐Galán Alfonso , Puiggalí Jordi
Published: March 2004

Summary: A new method for the preparation of poly(ester amide)s derived from glycolic acid units has been developed. Glycolic acid units can be incorporated with a high yield into a nylon‐n or a nylon‐n,m. The synthesis is based on a final thermal polycondensation with the formation of a metal halide salt as a driving force. New poly(ester amide)s have high molecular weights, good mechanical behaviour, and variable thermal properties, giving rise to a group of materials with potential interest as biodegradable materials in applications like surgical sutures.

Results of the differential scanning calorimeter heating runs for the sodium (a) and potassium (b) salts of N‐chloroacetyl‐6‐aminohexanoic acid.

magnified image

Results of the differential scanning calorimeter heating runs for the sodium (a) and potassium (b) salts of N‐chloroacetyl‐6‐aminohexanoic acid.
Synthesis and Characterization of a Novel Calix[4]arene‐Based Periodic Mesoporous Organosilica
Authors: Liu Chunqing , Fu Lei , Economy James
Published: March 2004

Summary: A new calix[4]arene‐based periodic mesoporous organosilica has been synthesized using tetraethoxysilane (TEOS) and a calix[4]arene‐based silane monomer as the precursors and cetyltrimethylammonium bromide (CTAB) surfactant as the structure‐directing template, and is shown to be capable of visual detection and entrapment of NO2.

Synthesis of the novel mesoporous organosilica material containing covalently bound tetra‐O‐alkylated calix[4]arene hosts.

magnified image

Synthesis of the novel mesoporous organosilica material containing covalently bound tetra‐O‐alkylated calix[4]arene hosts.
Narrowly Distributed Dendronized Polymethacrylates by Reversible Addition‐Fragmentation Chain Transfer (RAFT) Polymerization
Authors: Zhang Afang , Wei Liuhe , Schlüter A. Dieter
Published: March 2004

Summary: RAFT is applied to the dendronized macromonomers of the first and second generation, 1 and 2, respectively. Good results are obtained in the presence of AIBN as radical initiator, with compound 6 as mediator and at mediator to monomer ratios of 2:200 for monomer 1 ($\overline M _{\rm n}$ = 320 000, PDI = 1.24) and monomer 2 ($\overline M _{\rm n}$ = 178 000, PDI = 1.20). The common characteristics of a controlled polymerization are reasonably met. The more sterically demanding G2 monomer 2 requires higher polymerization temperatures.

magnified image