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Paschalis Alexandridis - One of the best experts on this subject based on the ideXlab platform.

  • evolution in structural polymorphism of pluronic f127 poly ethylene oxide poly propylene oxide block copolymer in ternary systems with water and pharmaceutically acceptable organic solvents from glycols to oils
    Langmuir, 2000
    Co-Authors: Rouja Ivanova, And Bjo Lindma, Paschalis Alexandridis
    Abstract:

    The evolution in the self-assembly of an amphiphilic poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) (PEO-PPO-PEO) block copolymer in ternary systems with water and organic solvents of varying relative polarity is examined. The phase behavior and microstructure of two ternary systems consisting of Pluronic F127 (Poloxamer 407), water, and the pharmaceutically acceptable solvents propylene carbonate (4-methyl-1,3-dioxolan-2-one) or triacetin (glycerol triacetate) are presented. The microstructure of the lyotropic liquid crystalline phases formed and their characteristic length scales are determined from small-angle X-ray scattering (SAXS). The trends in the SAXS lattice spacing and the interfacial area per block copolymer molecule help establish the location of the solvents in the microstructure. The phase behavior of the two systems studied here is discussed in the context of ternary systems of Pluronic F127 with water and polar solvents (“glycols”, e.g., propylene glycol) or apolar organi...

  • poly ethylene oxide poly propylene oxide block copolymer surfactants
    Current Opinion in Colloid and Interface Science, 1997
    Co-Authors: Paschalis Alexandridis
    Abstract:

    Block copolymers consisting of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) can self-assemble in water and water/oil mixtures (where water is a selective solvent for PEO and oil a selective solvent for PPO) to form thermodynamically stable spherical micelles as well as an array of lyotropic liquid crystalline mesophases of varying morphology. Significant advances have been made over the past year on the identification of different morphologies, the delineation of the composition-temperature ranges where they occur, and the structural characterization of the morphologies using primarily small angle scattering techniques. Important new findings on the copolymer micellization in water as affected by cosolutes, and on the time-dependency of the surface activity have also been reported.

Dimitrios N Bikiaris - One of the best experts on this subject based on the ideXlab platform.

  • exploring next generation engineering bioplastics poly alkylene furanoate poly alkylene terephthalate paf pat blends
    Polymers, 2019
    Co-Authors: Niki Poulopoulou, Dimitrios N Bikiaris, Nejib Kasmi, Maria Siampani, Zoi Terzopoulou, Dimitris S Achilias, Dimitrios G Papageorgiou, George Z Papageorgiou
    Abstract:

    Polymers from renewable resources and especially strong engineering partially aromatic biobased polyesters are of special importance for the evolution of bioeconomy. The fabrication of polymer blends is a creative method for the production of tailor-made materials for advanced applications that are able to combine functionalities from both components. In this study, poly(alkylene furanoate)/poly(alkylene terephthalate) blends with different compositions were prepared by solution blending in a mixture of trifluoroacetic acid and chloroform. Three different types of blends were initially prepared, namely, poly(ethylene furanoate)/poly(ethylene terephthalate) (PEF/PET), poly(propylene furanoate)/poly(propylene terephthalate) (PPF/PPT), and poly(1,4-cyclohenedimethylene furanoate)/poly(1,4-cycloxehane terephthalate) (PCHDMF/PCHDMT). These blends’ miscibility characteristics were evaluated by examining the glass transition temperature of each blend. Moreover, reactive blending was utilized for the enhancement of miscibility and dynamic homogeneity and the formation of copolymers through transesterification reactions at high temperatures. PEF–PET and PPF–PPT blends formed a copolymer at relatively low reactive blending times. Finally, poly(ethylene terephthalate-co-ethylene furanoate) (PETF) random copolymers were successfully introduced as compatibilizers for the PEF/PET immiscible blends, which resulted in enhanced miscibility.

  • synthesis of biocompatible poly ɛ caprolactone block poly propylene adipate copolymers appropriate for drug nanoencapsulation in the form of core shell nanoparticles
    International Journal of Nanomedicine, 2011
    Co-Authors: Stavroula Nanaki, Kostas Pantopoulos, Dimitrios N Bikiaris
    Abstract:

    Poly(propylene adipate)-block-poly(ɛ-caprolactone) copolymers were synthesized using a combination of polycondensation and ring-opening polymerization of ɛ-caprolactone in the presence of poly(propylene adipate). Gel permeation chromatography was used for molecular weight determination, whereas hydrogen-1 nuclear magnetic resonance and carbon-13 nuclear magnetic resonance spectroscopy were employed for copolymer characterization and composition evaluation. The copolymers were found to be block while their composition was similar to the feeding ratio. They formed semicrystalline structures, while only poly(ɛ-caprolactone) formed crystals, as shown by wide angle X-ray diffraction. Differential scanning calorimetry data suggest that the melting point and heat of fusion of copolymers decreased by increasing the poly(propylene adipate) amount. The synthesized polymers exhibited low cytotoxicity and were used to encapsulate desferrioxamine, an iron-chelating drug. The desferrioxamine nanoparticles were self-assembled into core shell structures, had mean particle size <250 nm, and the drug remained in crystalline form. Further studies revealed that the dissolution rate was mainly related to the melting temperature, as well as to the degree of crystallinity of copolymers.

  • crystallization kinetics and melting behaviour of the novel biodegradable polyesters poly propylene azelate and poly propylene sebacate
    Macromolecular Chemistry and Physics, 2009
    Co-Authors: George Z Papageorgiou, Dimitris S Achilias, Dimitrios N Bikiaris
    Abstract:

    Novel biodegradable poly(propylene sebacate) (PPSeb) and poly(propylene azelate) (PPAz) polyesters were synthesized and fully characterized using WAXD, standard DSC, high-rate DSC, and modulated-temperature DSC. Multiple-melting behaviour, observed for samples isothermally crystallized from the melt, was attributed to sequential melting-recrystallization-remelting. Study of isothermal and nonisothermal crystallization kinetics revealed a higher crystallization rate for PPSeb compared to PPAz. The Avrami and the Lauritzen-Hoffman models were successfully applied to DSC measurements, using also data obtained after self-nucleation, in order to diminish the effect of primary nucleation. Finally, the effective activation energy was estimated using the differential isoconversional method of Friedman.

  • synthesis cocrystallization and enzymatic degradation of novel poly butylene co propylene succinate copolymers
    Biomacromolecules, 2007
    Co-Authors: George Z Papageorgiou, Dimitrios N Bikiaris
    Abstract:

    A series of poly(butylene-co-propylene succinate) (PBPSu) random copolyesters were synthesized and characterized using 1HNMR spectroscopy and viscometry. Tensile properties decreased with increasing propylene succinate (PSu) content. Cocrystallization and multiple melting behaviors were investigated. The copolymers showed a eutectic behavior. The minimum melting point corresponded to 75 mol % PSu. Wide-angle X-ray diffraction (WAXD) patterns showed that the copolymers with up to 60 mol % PSu units formed poly(butylene succinate) crystals. The interplanar spacings slightly differentiated. The copolymer with 11.5 mol % poly(propylene succinate) (PPSu) units formed PPSu crystals. The results indicated isodimorphic cocrystallization. The cocrystallization was thermodynamically analyzed using the Wendling-Suter model. The defect free energy decreased for copolymers with high PPSu content. The banded spherulites of the copolyesters were studied, and growth rates were analyzed using the Lauritzen-Hoffman theory. Enzymatic hydrolysis study, using Rhizopus delemar and Pseudomonas cepacia lipases, showed that degradation was faster for copolymers with high PSu content, compared even to the fast-degrading PPSu.

Zhiqiang Fan - One of the best experts on this subject based on the ideXlab platform.

  • regioselective and alternating copolymerization of carbonyl sulfide with racemic propylene oxide
    Macromolecules, 2013
    Co-Authors: Ming Luo, Xing-hong Zhang, Qi Wang, Zhiqiang Fan
    Abstract:

    We report the first example of a regioregular and fully alternating poly (propylene monothiocarbonate) (PPMTC) from the well-controlled copolymerization of two asymmetric monomers, carbonyl sulfide...

  • effect of the combined external electron donors on the structure and properties of polypropylene poly ethylene co propylene in reactor alloys prepared by high efficiency industrial ziegler natta catalyst
    Industrial & Engineering Chemistry Research, 2013
    Co-Authors: Zhiqiang Fan
    Abstract:

    In this work, a series of isotactic polypropylene/ethylene–propylene rubber (iPP/EPR) in-reactor alloys were prepared by high-efficiency industrial Ziegler–Natta catalyst with diphenyldimethoxysilane/dicyclopentyldimethoxysilane (DDS/D-donor) mixtures as external electron donors. The effects of the external electron donor on the structure and mechanical properties of the iPP/EPR in-reactor alloys were studied. According to the characterization results, the iPP/EPR in-reactor alloys were mainly composed of random poly(ethylene-co-propylene), multiblock poly(ethylene-co-propylene), and highly isotactic PP. For DDS/D-donor mixtures as external electron donors and triethylaluminum (TEA) as the cocatalyst, as the amount of D-donor in DDS/D-donor mixtures increased, the molecular weight of polypropylene homopolymer and the structural uniformity of multiblock poly(ethylene-co-propylene) increased, whereas when D-donor alone was used as the external electron donor, they decreased. However, the isotacticity of pol...

  • influence of cocatalyst on the structure and properties of polypropylene poly ethylene co propylene in reactor alloys prepared by mgcl2 ticl4 diester type ziegler natta catalyst
    Journal of Applied Polymer Science, 2011
    Co-Authors: Zhiqiang Fan
    Abstract:

    In this work, a series of polypropylene/poly(ethylene-co-propylene) (iPP/EPR) in-reactor alloys were prepared by MgCl2/TiCl4/diester type Ziegler-Natta catalyst with triethylaluminium/triisobutylaluminium (TEA/TIBA) mixture as cocatalyst. The influence of cocatalyst and external electron donor, e.g., diphenyldimethoxysilane (DDS) or dicyclopentyldimethoxysilane (D-donor), on the structure and mechanical properties of iPP/EPR in-reactor alloys were studied and discussed. According to the characterization results, PP/EPR was mainly composed of random poly(ethylene-co-propylene), segmented poly(ethylene-co-propylene), and high isotactic PP. Using TEA/TIBA mixture as cocatalyst and DDS as external electron donor, as TEA/TIBA ratio increased, the impact strength of iPP/EPR in-reactor alloys had an increasing trend. Using TEA/TIBA mixture as cocatalyst and D-donor as external electron donor, the impact strength of iPP/EPR in-reactor alloy were dramatically improved. In this case, the iPP/EPR in-reactor alloy prepared at TEA: TIBA = 4 : 1 was the toughest. The influence of cocatalyst and external electron donor on the flexural modulus and flexural strength could be ignored. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Byeongmoon Jeong - One of the best experts on this subject based on the ideXlab platform.

  • secondary structure effect of polypeptide on reverse thermal gelation and degradation of l dl poly alanine poloxamer l dl poly alanine copolymers
    Macromolecules, 2008
    Co-Authors: Min Kyung Joo, Youn Soo Sohn, Byeongmoon Jeong
    Abstract:

    Poly(alanine) end-capped poly(propylene glycol)−poly(ethylene glycol)−poly(propylene glycol) (PA−PLX−PA) aqueous solutions underwent sol-to-gel transition as the temperature increased. On the basis of FTIR spectra, circular dichroism spectra, 13C NMR spectra, transmission electron microscopic images, fluorescence spectra, and dynamic light scattering studies, increases in the β-sheet conformation of the polyalanine (PA) and dehydration of the poly(propylene glycol)−poly(ethylene glycol)−poly(propylene glycol) (PLX) were suggested as the sol-to-gel transition mechanism. The sol-to-gel transition temperature could be controlled by molecular parameters of the PA−PLX−PA such as molecular weight of PA, molecular weights of PLX, and l-Ala/dl-Ala ratio. The PA−PLX−PA was significantly degraded in the subcutaneous layer of rats over 15 days; however, it was stable in phosphate buffer saline over the same period of time. Poly(propylene glycol)/poly(ethylene glycol) block copolymers suffer from short gel duration f...

  • Thermogelling poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) disulfide multiblock copolymer as a thiol-sensitive degradable polymer.
    Biomacromolecules, 2006
    Co-Authors: Kyung Hwa Sun, Youn Soo Sohn, Byeongmoon Jeong
    Abstract:

    We report a reverse thermogelling poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) disulfide multiblock copolymer as a thiol-sensitive biodegradable polymer. The poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) aqueous solutions studied in this research underwent sol−gel−sol or sol−gel−sol−gel transition depending on the molecular weight and concentration of the polymer, whereas the corresponding disulfide multiblock copolymer aqueous solutions underwent sol−gel transition as the temperature increased in a range of 0−60 °C. The hydrophobic dye solubilization and dynamic light scattering of the polymer aqueous solution suggest that the poly(ethylene oxide-b-propylene oxide-b-ethylene oxide)s undergo unimer (3 nm) to micelle (12 nm) transition, whereas the disulfide multiblock copolymers undergo unimer (6 nm) to aggregated polymer (600 nm) transition as the temperature increases. The gel duration increased from 6 h (poly(ethylene oxide-b-propylene oxide-b-ethylene oxide)) to more than 12 days ...

Joseph M Metzger - One of the best experts on this subject based on the ideXlab platform.

  • spatial distribution of peo ppo peo block copolymer and peo homopolymer in lipid bilayers
    Langmuir, 2020
    Co-Authors: Mihee Kim, Wenjia Zhang, Frank Heinrich, Greg Haugstad, Guangcui Yuan, Sushil K Satija, Hannah S Seo, Joseph M Metzger
    Abstract:

    Maintaining the integrity of cell membranes is indispensable for cellular viability. Poloxamer 188 (P188), a poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO–PPO–PEO) triblo...

  • chemical end group modified diblock copolymers elucidate anchor and chain mechanism of membrane stabilization
    Molecular Pharmaceutics, 2017
    Co-Authors: Evelyne M Houang, Frank S Bates, Karen Haman, Mihee Kim, Wenjia Zhang, Dawn A Lowe, Yuk Y Sham, Timothy P Lodge, Benjamin J Hackel, Joseph M Metzger
    Abstract:

    Block copolymers can be synthesized in an array of architectures and compositions to yield diverse chemical properties. The triblock copolymer Poloxamer 188 (P188), the family archetype, consisting of a hydrophobic poly(propylene oxide) core flanked by hydrophilic poly(ethylene oxide) chains, can stabilize cellular membranes during stress. However, little is known regarding the molecular basis of membrane interaction by copolymers in living organisms. By leveraging diblock architectural design, discrete end-group chemistry modifications can be tested. Here we show evidence of an anchor and chain mechanism of interaction wherein titrating poly(propylene oxide) block end group hydrophobicity directly dictates membrane interaction and stabilization. These findings, obtained in cells and animals in vivo, together with molecular dynamics simulations, provide new insights into copolymer–membrane interactions and establish the diblock copolymer molecular architecture as a valuable platform to inform copolymer–bi...