Novel biodegradable shape memory material based on partial inclusion complex formation between alpha-cyclodextrin and poly(epsilon-caprolactone)

A novel shape memory material was prepared based on the formation of inclusion complexes between alpha-cyclodextrin (alpha-CD) and poly(epsilon-caprolactone) (PCL); the PCL-alpha-CD inclusion crystallites serve as a fixing phase, while free PCL crystallites serve as a reversible phase. The characteristics of the material were investigated and a mechanism for the shape memory behavior was proposed. This material showed good shape memory properties, with the recovery ratio exceeding 90% and the recovery time being less than 6 s at 90 degrees C. This PCL-alpha-CD partial inclusion complex lost about 50% (47.4 +/- 4.4%) weight within 45 days in presence of lipase, indicating its degradability. The shape memory and biodegradation properties of the well-designed polymer-alpha-CD complexes indicate great promise for this novel shape memory material.     

Study of the synthesis, crystallization, and morphology of poly(ethylene glycol)-poly(epsilon-caprolactone) diblock copolymers

Poly(ethylene glycol)-poly(epsilon-caprolactone) diblock copolymers PEG-PCL were synthesized by ring-opening polymerization of epsilon-caprolactone using monomethoxy poly(ethylene glycol) as the macroinitiator and calcium ammoniate as the catalyst. Obvious mutual influence between PEG and PCL crystallization was studied by altering the relative block length. Fixing the length of the PEG block (Mn = 5000) and increasing the length of the PCL block, the crystallization temperature of the PCL block rose gradually from 1 to about 35 degrees C while that of the PEG block dropped from 36 to -6.6 degrees C. Meanwhile, the melting temperature of the PCL block went up from 30 to 60 degrees C, while that of the PEG block declined from 60 to 41 degrees C. If the PCL block was longer than the PEG block, the former would crystallize first when cooling from a molten state and led to obviously imperfect crystallization of PEG and vice versa. And they both crystallized at the same temperature, if their weight fractions were equal. We found that the PEG block could still crystallize at -6.6 degrees C even when its weight fraction is only 14%. A unique morphology of concentric spherulites was observed for PEG5000-PCL5000. According to their morphology and real-time growth rates, it is concluded that the central and outer sections in the concentric spherulites were PCL and PEG, respectively, and during the formation of the concentric spherulite, the PEG crystallized quickly from the free space of the PCL crystal at the earlier stage, followed by outgrowing from the PCL spherulites in the direction of right angles to the circle boundaries until the entire area was occupied.     

Acid catalyzed transesterification as a route to poly(3-hydroxybutyrate-co-epsilon-caprolactone) copolymers from their homopolymers

Copolymers of (R)-3-hydroxybutyric acid (HB) and epsilon-caprolactone (CL) with a composition ranging from 28 to 81 mol % of HB were synthesized by transesterification of the corresponding homopolymers in solution in the presence of 4-toluenesulfonic acid. The copolyesters were characterized with regard to their molecular weights, thermal properties, molar compositions, and average block length of repeating units by gel permeation chromatography (GPC), differential scanning calorimetry, (1)H NMR, and (13)C NMR, respectively. Random and microblock copolymers could be obtained depending on experimental conditions, with weight-average molecular weights of up to 20,000. The glass transition temperature decreased from 2 to -42 degrees C as the CL content was increased from 0 to 72 mol %. The melting temperature (T(m)) of the PCL phase decreased from 70 to 46 degrees C as the HB content changed from 0 to 47 mol %, while the T(m) of the PHB phase decreased from 177 degrees C to 163 degrees C as the CL content changed from 0 to 72 mol %. Matrix-assisted laser desorption ionization time-of-flight mass spectra of GPC fractionated samples allowed us to ascertain that copolymers rich in HB units have mostly hydroxyl and carboxyl end groups, while copolymers rich in CL units have mostly tosyl and carboxyl end groups.     

XRD studies of chitin-based polyurethane elastomers

Chitin-based polyurethane elastomers (PUEs) were synthesized by step growth polymerization techniques using poly(epsilon-caprolactone) (PCL) varying diisocyanate and chain extender structures. The viscosity average molecular weight (M(v)) of chitin was deduced from the intrinsic viscosity and found; M(v)=6.067 x 10(5). The conventional spectroscopic characterization of the samples with FTIR, (1)H NMR and (13)C NMR were in accordance with proposed PUEs structure. The crystalline behavior of the synthesized polymers were investigated by X-ray diffraction (XRD), differential scanning calorimetery (DSC) and loss tangent curves (tan delta peaks). The observed patterns of the crystalline peaks for the lower angle for chitin in the 2theta range were indexed as 9.39 degrees, 19.72 degrees, 20.73 degrees, 23.41 degrees and 26.39 degrees. Results showed that crystallinity of the synthesized PUEs samples was affected by varying the structure of the diisocyanate and chain extender. Crystallinity decreased from aliphatic to aromatic characters of the diisocyanates used in the final PU. The presence of chitin also favors the formation of more ordered structure, as higher peak intensities was obtained from the PU extended with chitin than 1,4-butane diol (BDO). The value of peak enthalpy (DeltaH) of chitin was found to be 47.13 J g(-1). The higher DeltaH value of 46.35 J g(-1) was found in the samples extended with chitin than BDO (39.73 J g(-1)).     

Effects of residual zinc compounds and chain-end structure on thermal degradation of poly(epsilon-caprolactone)

Effects of chain-end structure and residual metal compounds on thermal degradation of poly(epsilon-caprolactone) (PCL) were investigated by means of thermogravimetric and pyrolysis-gas chromatograph mass spectrometric analyses. Four types of PCL samples with different chain-end structures (alpha-carboxylic acid-omega-hydroxyl-PCL, alpha-dodecyl ester-omega-hydroxyl-PCL, alpha-carboxylic acid-omega-acetyl-PCL, and alpha-dodecyl ester-omega-acetyl-PCL) were prepared by ring-opening polymerization of epsilon-caprolactone in the presence of zinc-based catalyst and by subsequent acetylation reaction of polymers with acetic anhydride. PCL samples with different zinc contents were obtained by washing with acetic acid in chloroform solution of polymer. Thermal degradation behaviors of these PCL samples with different chain-end structures were examined under both isothermal and nonisothermal conditions. From both the isothermal and nonisothermal experiments, the thermal degradation of PCL samples containing high amounts of residual zinc compounds from synthesis process revealed the selective unzipping depolymerization step below 300 degrees C producing epsilon-caprolactone exclusively. In contrast, zinc-free PCL samples were stable at temperatures below 300 degrees C, and the thermal degradation occurred only at temperatures above 300 degrees C regardless of the chain-end structure. From (1)H NMR analysis of the residual molecules after isothermal degradation of zinc-free PCL, it was confirmed that the omega-chain-end of residual molecules was 5-hexenoic acid unit. However, the cyclic monomer and oligomers were detected as the volatile products of zinc-free PCL samples. These results suggest that the dominant reaction of thermal degradation for PCL above 300 degrees C is a competition between the random chain scission via cis elimination reaction and the cyclic rupture via intramolecular transesterification of PCL molecules.     

Shape-memory polymer networks from oligo[(epsilon-hydroxycaproate)-co-glycolate]dimethacrylates and butyl acrylate with adjustable hydrolytic degradation rate

Degradable shape-memory polymer networks intended for biomedical applications were synthesized from oligo[(epsilon-hydroxycaproate)-co-glycolate]dimethacrylates with glycolate contents between 0 and 30 mol % using a photopolymerization process. In addition AB copolymer networks were prepared by adding 60 wt % n-butyl acrylate as comonomer. All synthesized polymer networks are semicrystalline at room temperature. A melting transition T(m) between 18 and 53 degrees C which can be used as switching transition for the shape-memory effect can be attributed to the crystalline poly(epsilon-hydroxycaproate) phase. At temperatures below T(m) the elastic properties are dominated by these physical cross-links. At temperatures higher than T(m) the E modulus of the amorphous polymer networks is lowered by up to 2 orders of magnitude, depending on the chemical cross-link density. Copolymer networks based on macrodimethacrylates with a M(n) of up to 13,500 g x mol(-1) and a maximum glycolate content of 21 mol % show quantitative strain recovery rates in stress-controlled cyclic thermomechanical experiments. Hydrolytic degradation experiments of polymer networks performed in phosphate buffer solution at 37 degrees C show that the degradation rate can be accelerated by increasing the glycolate content and decelerated by the incorporation of n-butyl acrylate.     

Synthesis, characterization and thermal properties of chitin-g-poly(epsilon-caprolactone) copolymers by using chitin gel

Chitin is known to be natural polymer and it is non-toxic, biodegradable and biocompatible. The chitin-g-poly(epsilon-caprolactone) (chitin-g-PCL) copolymer was prepared by the ring-opening polymerization of epsilon-caprolactone onto chitin gel in the presence of tin(II) 2-ethylhexanoate catalyst by bulk polymerization method under homogeneous system. The prepared copolymer were characterized by FT-IR, (13)C NMR, thermogravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron microscopy (SEM), solubility and X-ray diffraction (XRD). The degree of substitution of chitin-g-PCL copolymer was found to be 0.48. The TGA analysis showed that chitin-g-PCL was slightly less thermal stability than original chitin. It was due to the grafting of PCL reduced the crystalline structure of chitin. DTA analysis of chitin-g-PCL showed the two exothermic peaks between 300 and 400 degrees C. The first peak at 342 degrees C was due to chitin peak and the second peak was due to PCL. These results suggested that chitin and PCL chains were mixed well at a molecular level. The XRD pattern analysis of chitin-g-PCL showed a weak and broader peak, which demonstrated that the conjugation of PCL with chitin suppressed the crystallization of both chitin and PCL to some extent. The SEM studies showed that the chitin gel seems have a smooth surface morphology, but the chitin-g-PCL showed slightly rough morphology due to the grafting of PCL into chitin. The surface morphology studies also confirmed the grafting reaction.     

Lipase-catalyzed synthesis of aliphatic polyesters via copolymerization of lactone, dialkyl diester, and diol

Candida antarctica lipase (CALB) has been successfully used as catalyst for copolymerization of dialkyl diester with diol and lactone to form aliphatic polyesters. The polymerization reactions were performed using a two stage process: first stage oligomerization under low vacuum followed by second stage polymerization under high vacuum. Use of the two-stage process is required to obtain products with high molecular weights at high yields for the following reasons: (i) the first stage reaction ensures that the monomer loss via evaporation is minimized to maintain 1:1 diester to diol stoichiometric ratio, and the monomers are converted to nonvolatile oligomers; (ii) use of high vacuum during the second stage accelerates equilibrium transesterification reactions to transform the oligomers to high molecular weight polymers. Thus, terpolymers of omega-pentadecalactone (PDL), diethyl succinate (DES), and 1,4-butanediol (BD) with a M w of whole product (nonfractionated) up to 77000 and M w/ M n between 1.7 and 4.0 were synthesized in high yields (e.g., 95% isolated yield). A desirable reaction temperature for the copolymerizations was found to be around 95 degrees C. At 1:1:1 PDL/DES/BD monomer molar ratio, the resultant terpolymers contained equal moles of PDL, succinate, and butylene repeat units in the polymer chains. (1)H and (13)C NMR analyses were used to determine the polyester microstructures. The synthesized PDL-DES-BD terpolymers possessed near random structures with all possible combinations of PDL, succinate, and butylene units via ester linkages in the polymer backbone. Furthermore, thermal stability and crystallinity of a pure PDL-DES-BD terpolymer with 1:1:1 PDL to succinate to butylene unit ratio and M w of 85400 were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The copolyester was found to be a semicrystalline material with a T g of -34 degrees C and a T m of 64 degrees C, which degrades in a single weight loss step centered at T max = 408 degrees C.     

Syntheses, characterization, and in vitro degradation of ethyl cellulose-graft-poly(epsilon-caprolactone)-block-poly(L-lactide) copolymers by sequential ring-opening polymerization

Well-defined ethyl cellulose-graft-poly(epsilon-caprolactone) (EC-g-PCL) graft copolymers were successfully synthesized via ring-opening polymerization (ROP) of epsilon-caprolactone (CL) with an ethyl cellulose (EC) initiator and a tin 2-ethylhexanoate (Sn(Oct)2) catalyst in xylene at 120 degrees C. Then, novel ethyl cellulose-graft-poly(epsilon-caprolactone)-block-poly(L-lactide) (EC-g-PCL-b-PLLA) graft-block copolymers were prepared by ROP of L-lactide (L-LA) with a hydroxyl-terminated EC-g-PCL macroinitiator and Sn(Oct)2 catalyst in bulk at 120 degrees C. Various graft and block lengths of EC-g-PCL and EC-g-PCL-b-PLLA copolymers were obtained by adjusting the molar ratios of CL monomer to EC and the L-LA monomer to CL. The thermal properties and crystalline morphologies of EC-g-PCL and EC-g-PCL-b-PLLA copolymers were different from those of linear PCL. The in vitro degradation rate of EC-g-PCL-b-PLLA was faster than those of linear PCL and EC-g-PCL due to the presence of PLLA blocks.     

Synthesis of biodegradable poly-epsilon-caprolactone microspheres by dispersion ring-opening polymerization in supercritical carbon dioxide

A series of fluorinated diblock and triblock copolymers of poly(epsilon-caprolactone) and poly(heptadecafluorodecylacrylate) were prepared by combining ring-opening polymerization of epsilon-CL and atom transfer radical polymerization of the acrylate. These copolymers with well-controlled molecular weight and composition were characterized by (1)H NMR spectroscopy and used as stabilizers for the dispersion ring-opening polymerization of epsilon-CL in supercritical carbon dioxide. The effect of composition and architecture of the polymeric stabilizers on the stabilization of PCL microspheres was investigated. Finally, purification of PCL was successfully implemented by reactive supercritical fluid extraction of the tin catalyst.     

Living ring-opening polymerization of a carbohydrate-derived lactone for the synthesis of protein-resistant biomaterials

An efficient living ring-opening polymerization (ROP) of a permethoxylated epsilon-caprolactone [(OMe)CL] catalyzed by yttrium(III) isopropoxide was developed for the synthesis of degradable protein-resistant polymers [P(OMe)CL]. The lactone monomer was efficiently prepared from a reduced sugar, D-dulcitol. Kinetic studies of the ROP revealed a linear dependence of ln[M]0/[M] on polymerization time as well as a linear correlation between the number-averaged molecular weight (M(n)) and monomer conversion; both support it is a living polymerization. A series of block copolymers of our permethoxylated lactone with epsilon-caprolactone [P(OMe)CL-b-PCL] were synthesized and fully characterized. In thermal analyses only single T(g)s were observed in all the block copolymers, suggesting that P(OMe)CL and PCL blocks are fully miscible. Finally, surface plasmon resonance (SPR) sensograms demonstrated that both P(OMe)CL and the P(OMe)CL-b-PCL block copolymers exhibit excellent resistance to fibrinogen and lysozyme.     

Formation of a unique crystal morphology for the poly(ethylene glycol)-poly(epsilon-caprolactone) diblock copolymer

The crystallization behaviors of the poly(ethylene glycol)-poly(epsilon-caprolactone) diblock copolymer with the PEG weight fraction of 0.50 (PEG(50)-PCL(50)) was studied by DSC, WAXD, SAXS, and FTIR. A superposed melting point at 58.5 degrees C and a superposed crystallization temperature at 35.4 degrees C were obtained from the DSC profiles running at 10 degrees C/min, whereas the temperature-dependent FTIR measurements during cooling from the melt at 0.2 degrees C/min showed that the PCL crystals formed starting at 48 degrees C while the PEG crystals started at 45 degrees C. The PEG and PCL blocks of the copolymer crystallized separately and formed alternating lamella regions according to the WAXD and SAXS results. The crystal growth of the diblock copolymer was observed by polarized optical microscope (POM). An interesting morphology of the concentric spherulites developed through a unique crystallization behavior. The concentric spherulites were analyzed by in situ microbeam FTIR, and it was determined that the morphologies of the inner and outer portions were mainly determined by the PCL and PEG spherulites, respectively. However, the compositions of the inner and outer portions were equal in the analysis by microbeam FTIR.     

Purification and partial characterization of polygalacturonase from Streptomyces lydicus

Polygalacturonase produced by Streptomyces lydicus was purified to homogeneity by ultrafiltration and a combination of ion exchange and gel filtration chromatographic procedures. The purified enzyme was an exo-polygalacturonase with a molecular weight of 43 kDa. It was optimally active at 50 degrees C and pH 6.0. The enzyme was stable from pH 4.0 to 7.0 and at or below 45 degrees C for 90 min. K(m) value for polygalacturonic acid was 1.63 mg/mL and the corresponding V(max) was 677.8 microM min(-1) mg(-1). The inhibition constant (K(i)) for gluconic acid d-lactone was 20.75 mM. Purified enzyme had been inhibited by N-bromosuccinimide, while l-tryptophan could induce enzyme activity, indicating the involvement of tryptophan at the active site.     

Cocrystallization of random copolymers of omega-pentadecalactone and epsilon-caprolactone synthesized by lipase catalysis

Random copolymers were prepared by Candida antarctica lipase B (Novozyme-435) catalyzed copolymerization of omega-pentadecalactone (PDL) with epsilon-caprolactone (CL). Over the whole composition range PDL-CL copolymers are highly crystalline (melting enthalpy by differential scanning calorimetry, above 100 J/g; crystallinity degree by wide-angle X-ray scattering, WAXS, 60-70%). The copolymers melt at temperatures that linearly decrease with composition from that of poly(omega-pentadecalactone) (PPDL; 97 degrees C) to that of poly(epsilon-caprolactone) (PCL; 59 degrees C). The WAXS profiles of PCL and PPDL homopolymers are very similar, except for the presence in PPDL of the (001) reflection at 2theta = 4.58 degrees that corresponds to a 19.3 angstroms periodicity in the chain direction. In PDL-CL copolymers the intensity of this reflection decreases with increasing content of CL units and vanishes at 50 mol % CL, as a result of randomization of the ester group alignment and loss of chain periodicity. PDL-CL copolymers crystallize in a lattice that gradually changes from that of one homopolymer to that of the other, owing to comonomer isomorphous substitution. Cocrystallization of comonomer units is also shown by a random PDL-CL copolymer obtained in a polymerization/transesterification reaction catalyzed by C. antarctica lipase B (Novozyme-435) starting from preformed PCL and PDL monomer.     

Supramolecular Polypseudorotaxanes composed of star-shaped porphyrin-cored poly(epsilon-caprolactone) and alpha-cyclodextrin

Star-shaped porphyrin-cored poly(epsilon-caprolactone) (SPPCL) was synthesized using a tetrahydroxyethyl-terminated porphyrin as a core initiator and stannous octoate as a catalyst in bulk at 120 degrees C. The molecular weight of as-synthesized polymer could be adjusted linearly by controlling the molar ratio of epsilon-caprolactone to porphyrin core initiator, and the molecular weight distribution was reasonably narrow. Supramolecular polypseudorotaxanes were prepared by inclusion complexation of SPPCL with alpha-cyclodextrin (alpha-CD) and thoroughly characterized by means of FT-IR, 1H NMR, 13C CP/MAS NMR, DSC, TGA, and WAXD. The results demonstrated that the porphyrin-cored polypseudorotaxanes formed through alpha-CD molecules threading onto the branch chains of star-shaped SPPCL polymers, and they had a channel-type crystalline structure. Meanwhile, the original crystallization of SPPCL polymers within the polypseudorotaxanes was completely suppressed in the alpha-CD cavities. Moreover, inclusion complexation between SPPCL and alpha-CD enhanced the thermal stability of both the guest SPPCL polymers and the host alpha-CD. Furthermore, both the SPPCL polymers and the polypseudorotaxanes showed similar fluorescent and UV-vis spectra compared with porphyrin core initiator. Consequently, this will not only provide potentially porphyrin-cored poly(epsilon-caprolactone) and its polypseudorotaxanes for photodynamic therapy but also improve the compatibility between poly(epsilon-caprolactone) and peptide drugs for drug delivery.     

Melt electrospinning of poly-(ethylene glycol-block-epsilon-caprolactone)

Various block copolymers of poly(ethylene glycol) and poly(epsilon-caprolactone) (PEG-b-PCL) with molecular weights between 7000 and 26,900 g/mol were synthesized, and melt electrospun at temperatures between 60 degrees C and 90 degrees C. Two types of fibers were collected, including excellent quality fibers - highly coiled and continuous, with a constant diameter and relatively defect free. Such fibers, termed "solid fibers", were sufficiently cooled during their path between the spinneret and the collector that the symmetric fiber shape is maintained after landing on the collector. The second type of melt electrospun fiber were poor quality, large diameter fibers, flattened on the collector - termed "molten fibers". The solid and molten fibers were morphologically distinct from each other as determined from scanning electron microscopy (SEM). Using an SEM imaging method to assess the regional variations of collected electrospun material, we found the spinneret pump rate largely influenced the fiber quality. The polymer flow rate to the spinneret and the molecular weight of PEG-b-PCL had the greatest effect on the electrospun fibers collected, with an optimum rate of 0.05-0.1 mL/h for the highest molecular weight copolymers. The lowest molecular weight PEG-b-PCL tended to electrospray, while the material collected from higher molecular weight copolymers were conducive to fiber formation. The highest quality fibers were PEG-b-PCL block copolymers (22,000 and 26,900 g/mol) melt electrospun at temperatures of 85 degrees C and 90 degrees C, corresponding to shear viscosities of the polymer of between 28.1 and 39.4 Pa.S.     

Composition dependence of the crystallization behavior and morphology of the poly(ethylene oxide)-poly(epsilon-caprolactone) diblock copolymer

The crystallization behavior and morphology of the crystalline-crystalline poly(ethylene oxide)-poly(epsilon-caprolactone) diblock copolymer (PEO-b-PCL) was studied by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), small-angle X-ray scattering (SAXS), and hot-stage polarized optical microscope (POM). The mutual effects between the PEO and PCL blocks were significant, leading to the obvious composition dependence of the crystallization behavior and morphology of PEO-b-PCL. In this study, the PEO block length was fixed (Mn = 5000) and the weight ratio of PCL/PEO was tailored by changing the PCL block length. Both blocks could crystallize in PEO-b-PCL with the PCL weight fraction (WFPCL) of 0.23-0.87. For the sample with the WFPCL of 0.36 or less, the PEO block crystallized first, resulting in the obvious confinement of the PCL block and vice versa for the sample with WFPCL of 0.43 or more. With increasing WFPCL, the crystallinity of PEO reduced continuously while the variation of the PCL crystallinity exhibited a maximum. The long period of PEO-b-PCL increased with increasing WFPCL from 0.16 to 0.50 but then decreased with the further increase of WFPCL due to the interaction of the respective variation of the thicknesses of the PEO and PCL crystalline lamellae. Only the PEO spherulites were observed in samples with WFPCL of 0.16-0.36 by POM, in contrast to only the PCL spherulites in samples with WFPCL of 0.56-0.87. For samples with WFPCL of 0.43 and 0.50, a unique concentric spherulite was observed. The morphology of the inner and outer portions of the concentric spherulites was determined by the PCL and PEO spherulites, respectively. The growth rate of the PEO spherulites reduced rapidly with increasing WFPCL from 0 to 0.50. However, when increasing WFPCL from 0.43 to 0.87, the variation of the growth rate of the PCL spherulites exhibited a maximum rather than a monotonic change.     

Light-induced transpiration alters cell water relations in figleaf gourd (Cucurbita ficifolia) seedlings exposed to low root temperatures

Water relation parameters including elastic modulus (epsilon), half-times of water exchange (T(w)(1/2)), hydraulic conductivity and turgor pressure (P) were measured in individual root cortical and cotyledon midrib cells in intact figleaf gourd (Cucurbita ficifolia) seedlings, using a cell pressure probe. Transpiration rates (E) of cotyledons were also measured using a steady-state porometer. The seedlings were exposed to low ambient (approximately 10 micromol m(-2) s(-1)) or high supplemental irradiance (approximately 300 micromol m(-2) s(-1) PPF density) at low (8 degrees C) or warm (22 degrees C) root temperatures. When exposed to low irradiance, all the water relation parameters of cortical cells remained similar at both root temperatures. The exposure of cotyledons to supplemental light at warm root temperatures, however, resulted in a two- to three-fold increase in T(w)(1/2) values accompanied with the reduced hydraulic conductivity in both root cortical (Lp) and cotyledon midrib cells (Lp(c)). Low root temperature (LRT) further reduced Lp(c) and E, whether it was measured under low or high irradiance levels. The reductions of Lp as the result of respective light and LRT treatments were prevented by the application of 1 microM ABA. Midrib cells required higher concentrations of ABA (2 microM) in order to prevent the reduction in Lp(c). When the exposure of cotyledons to light was accompanied by LRT, however, ABA proved ineffective in reversing the inhibition of Lp. LRT combined with high irradiance triggered a drastic 10-fold reduction in water permeability of cortical and midrib cells and increased epsilon and T(w)(1/2) values. Measurement of E indicated that the increased water demand by the transpiring plants was fulfilled by an increase in the apoplastic pathway as principal water flow route. The importance of water transport regulation by transpiration affecting the hydraulic conductivity of the roots is discussed.     

Synthesis of poly(epsilon-caprolactone)-b-poly(gamma-benzyl-L-glutamic acid) block copolymer using amino organic calcium catalyst

A biodegradable two block copolymer, poly(epsilon-caprolactone)-b- poly(gamma-benzyl-L-glutamic acid) (PCL-PBLG) was synthesized successfully by ring-opening polymerization of N-carboxyanhydride of gamma-benzyl-L-glutamate (BLG-NCA) with aminophenyl-terminated PCL as a macroinitiator. The aminophenethoxyl-terminated PCL was prepared via hydrogenation of a 4-nitrophenethoxyl-terminated PCL, which was novelly obtained from the polymerization of epsilon-caprolactone (CL) initiated by amino calcium 4-nitrobenzoxide. The structures of the block copolymer and its precursors from the initial step of PCL were confirmed and investigated by 1H NMR, FT-IR, GPC, and FT-ICRMS analyses and DSC measurements.     

Polycaprolactone-poly(ethylene glycol) multiblock copolymers as potential substitutes for di(ethylhexyl) phthalate in flexible poly(vinyl chloride) formulations

New high-molecular-weight hydrophobic/hydrophilic segmented copolymers of poly(ester ether carbonate) structure, containing poly(epsilon-caprolactone) (PCL) and poly(ethylene glycol) (PEG) segments in their main chain, were synthesized and characterized. These copolymers were obtained by a two-step chain-extension reaction carried out in the presence of alpha,omega-dihydroxy-oligoPCL of molecular weight 1250 and PEG samples of molecular weight 150, 400, 600, 1000, and 2000. The molecular structures of all synthesized materials were characterized by means of (1)H NMR and (13)C NMR spectroscopy, their molecular weights were determined by means of size exclusion chromatography, and their thermal properties were obtained by means of differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The poly(ester ether carbonate)s of this study are partly or totally miscible at least up to 50 wt % with poly(vinyl chloride) (PVC) and could be used to produce flexible PVC formulations. The miscibility between PVC and the poly(ester ether carbonate)s reported in this paper was investigated by means of DSC and DMA analysis. PVC blends were also analyzed by determining their swellability and the amount of extractables in aqueous media. By comparison purposes, the chain-extension product of PCL1250, that is, PCL polycarbonate, was also synthesized and characterized. The results obtained demonstrated that the copolymers with shortest PEG segment length, i.e. PEG150, 400, and 600, give the best results in terms of miscibility with PVC and lead to blends with maximum resistance to extraction by water. Therefore, they represent, in principle, good substitutes for low-molecular-weight, leachable PVC plasticizers, such as di(ethylhexyl) phthalate.