Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Selected Abstracts

Linear-dendritic copolymers as nanocatalysts

M. Adeli
Abstract Functionalized poly(ethylene glycol) (PEG) containing four chloride end functional groups (PEG-Cl4) was synthesized through reaction between cyanuric chloride and PEG-(OH)2. Chloride end functional groups of PEG-Cl4 were able to initiate the ring opening polymerization of 2-ethyl-2-oxazoline and star copolymers containing a PEG core, and poly(2-ethyl-2-oxazoline) (POX) arms were obtained. Polymerization was quenched using diethanolamine, and star copolymers containing hydroxyl end functional groups (PEG-POX-OH) were obtained. ,-Caprolactone was then polymerized using the hydroxyl end functional groups of star copolymers and amphiphilic linear-dendritic copolymers containing PEG and POX, and poly(caprolactone) (PCL) blocks were synthesized. Linear-dendritic copolymers were able to load the organic and inorganic guest molecules. Application of host-guest systems such as nanocatalyst for Heck chemical reaction was also investigated. 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]

New Biodegradable Amphiphilic Block Copolymers of , -Caprolactone and , -Valerolactone Catalyzed by Novel Aluminum Metal Complexes

Jing Yang
Abstract Summary: In our previous study [J. Yang, L. Jia, L. Yin, J. Yu, Z. Shi, Q. Fang, A. Cao, Macromol. Biosci.2004, 4, 1092.], new biodegradable copolymers of diblock methoxy poly(ethylene glycol)- block -poly(, -caprolactone) and methoxy poly(ethylene glycol)- block -poly(, -valerolactone), and triblock poly(, -caprolactone)- block -poly(ethylene glycol)- block -poly(, -caprolactone) and poly(, -valerolactone)- block -poly(ethylene glycol)- block -poly(, -valero-lactone) bearing narrow molecular weight distributions and well-defined block architectures were reported to be prepared with our original aluminum metal complex templates. This work will continue to report new investigations on their water solubility, and reversible thermal responsive micellization and solution to gel transition in distilled water. Among the new synthesized copolymers (P1,P23), seven diblock or triblock samples (P3, P6, P7, P11, P12, P19, and P21) with higher hydrophilic building block populations were revealed to be water soluble under ambient temperature. By means of UV spectrophotometer attached with a thermostat, important parameters as critical micellization mass concentrations (CMCs) and critical micellization temperatures (CMTs) were characterized for these new amphiphile dilute aqueous solution with the aid of an lipophilic organic dye probe of 1,6-diphenyl-1,3,5-hexatriene (DPH). Furthermore, the critical gelation temperatures (CGTs) were simultaneously investigated for these water-soluble block copolymers via a tube tilting method. It was found that the CMC, CMT, and CGT were strongly affected by the population and nature of the hydrophobic building blocks, and a higher hydrophobicity of the new amphiphilic block copolymer finally led to lower CMC and CMT, and higher CGT. In addition, the salts of KBr and NaCl were found to play as a salt-out effect on the solution to gel transition for the diblock P6 and triblock P11, exhibiting an interesting tunable gelation temperature close to 35,42,C. These results will pave new possibility for the synthesized block structural amphiphiles as potential biomaterials to be applied in vivo. Thermal responsive micellization and gelation of diblock MPEG- b -PCL/PVL and triblock PVL/PCL- b -PEG- b -PCL/PVL. [source]

Photocurable Shape-Memory Copolymers of , -Caprolactone and L -Lactide

Minoru Nagata
Abstract Biodegradable and photocurable block copolymers of , -caprolactone and L -lactide were synthesized by polycondensation of PLLA diol (,=,10,000,g,,mol,1), PCL diol (,=,10,000,g,,mol,1), and a chain extender bearing a coumarin group. The effect of copolymer composition on the thermal and mechanical properties of the photocured copolymers was studied by means of DSC and cyclic tensile tests. An increase in Young's modulus and a decrease in the tensile strain with increasing PLLA content was observed for the block copolymers. Block copolymers with high PCL content showed good to excellent shape-memory properties. Random copolymers exhibited Rf and Rr values above 90% at 45,C for an extremely large tensile strain of 1,000%. [source]

Synthesis and Characterization of Block Copolymers of , -Caprolactone and DL -Lactide Initiated by Ethylene Glycol or Poly(ethylene glycol)

Ming-Hsi Huang
Abstract Biodegradable copolymers were prepared by ring-opening polymerization of sequentially added , -caprolactone and DL -lactide in the presence of ethylene glycol or poly(ethylene glycol), using zinc metal as catalyst. Polymerization was performed in bulk and yielded block copolymers with predetermined PEG/PCL/PLA segments. The obtained polymers were characterized by 1H NMR, SEC, IR, DSC, TGA, and X-ray diffraction. Data showed that the copolymers preserved the excellent thermal behavior inherent to PCL. The crystallinity of PLA-containing copolymers was reduced with respect to PCL homopolymer. The presence of both hydrophilic PEG and fast degrading PLA blocks should improve the biocompatibility and biodegradability of the materials, which are of interest for applications as substrate in drug delivery or as scaffolding in tissue engineering. Block copolymerization of , -caprolactone and DL -lactide initiated by dihydroxyl PEG. [source]

Morphology and Crystalline Structure of Poly(, -Caprolactone) Nanofiber via Porous Aluminium Oxide Template

Yang Chen
Abstract Summary: Poly(, -caprolactone) (PCL) nanofibers with a dimension of about 150 nm were successfully fabricated by using a process of extruding PCL solution via a porous aluminium oxide template and then solidifying in methanol. The morphology, melting behavior and crystalline structure of the nanofibers were investigated by using scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results revealed that the weight-average molecular weight () of PCL hardly influenced the morphology of the nanofibers. However, the melting temperature (Tm) of the PCL crystalline increased slightly from 55.4 to 57.5,C with an increase in . The accessional pressure and the presence of the porous template played an important role in the improvement of the orientation and crystallization structures of the polymer chains when they were passing through the nano-scale porous channel, leading to the conglomeration of the fiber and the much larger diameter than those from the pressure-induced extrusion process. Furthermore, comparing the processes with and without accessional pressure, the crystallinity of the nanofibers obtained under 0.2 MPa pressure increased, and the diffraction for the (001) lattice plane occurred. SEM image of PCL nanofibers extruded via a porous aluminium oxide template with the aid of pressure. [source]

Influence of Microwave Irradiation on the Lipase-Catalyzed Ring-Opening Polymerization of , -Caprolactone

Patrick Kerep
Abstract Summary: The microwave (MW)-assisted lipase-catalyzed ring-opening polymerization of , -caprolactone in boiling solvents was investigated for the first time. In case of boiling toluene or benzene the MW-assisted reaction proceeded significantly slower compared to oil bath heating. On the other hand, using boiling diethyl ether as solvent, an increase of the polymerization rate due to MW irradiation was found. Yield, molecular weight measurements, and MALDI-TOF analysis supported the results. Reactivity of the MW-assisted ring-opening polymerization of , -caprolactone compared with conventional thermal heating in different solvents. [source]

Lanthanide Thiolate Complexes: Novel Initiators for Ring-opening Polymerization of ,-Caprolactone

Hong-Mei Sun
Abstract The ring-opening polymerization (ROP) of , -caprolactone (, -CL) using lanthanide thiolate complexes [(CH3C5H4)2Sm(,-SPh)(THF)] 2 (1) and Sm(SPh)3(HMPA)3 (2) as initiators has been investigated for the first time. Both of 1 and 2 were found to be highly efficient initiators for the ROP of , -CL. The poly(, -caprolactone) (PCL) with molecular weight Mn up to 1.97105 and relatively narrow molecular weight distributions (1.20< Mw/Mn<2.00) have been obtained in high yield in the temperature range of 35,65 C. According to the polymer yield, 2 showed much higher activity than 1. However, the number-average molecular weight of PCL obtained with 2 was much lower than with 1. The possible polymerization mechanism of the , -CL polymerization has been proposed based on the results of the end group analysis of the , -CL oligomer. [source]

Bis(phosphinimino)methanides as Ligands in Divalent Samarium Chemistry: Synthesis, Structures and Catalysis

Michal Wiecko
Abstract The reaction of K{CH(PPh2NSiMe3)2} with samarium diiodide in a 1:1 molar ratio in thf affords the corresponding divalent samarium complex [{(Me3SiNPPh2)2CH}Sm(,-I)(thf)]2 (1), whereas treatment of K{CH(PPh2NSiMe3)2} with samarium diiodide in a 2:1 molar ratio in thf gives the homoleptic complex [{(Me3SiNPPh2)2CH}2Sm] (2). When 1 is treated with KNPh2 in toluene in a 2:1 molar ratio the mixed dimeric compound [({(Me3SiNPPh2)CH}2Sm)2(,-I)(,-NPh2)] (3) is obtained. The single-crystal X-ray structures of all these complexes have been determined. [{(Me3SiNPPh2)2CH}Sm(,-I)(thf)]2 has also been successfully used as a catalyst for the polymerization of ,-caprolactone. Good activities and molecular masses are observed with this catalyst.( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Annealing of Biodegradable Polymer Induced by Femtosecond Laser Micromachining,

Wai Yee Yeong
Abstract Femtosecond laser is a potential tool for net shape processing of biodegradable polymers. However, laser processing of polymeric material is still a challenge and the effects induced by laser ablation needs to be investigated. Poly(, -caprolactone) was micromachined at high fluence and the heat affected zone was characterized. Two different phases of microstructure, namely the annealed spherulite zone and the amorphous zone, are found. [source]

Porous Polymersomes with Encapsulated Gd-Labeled Dendrimers as Highly Efficient MRI Contrast Agents

Zhiliang Cheng
Abstract The use of nanovesicles with encapsulated Gd as magnetic resonance (MR) contrast agents has largely been ignored due to the detrimental effects of the slow water exchange rate through the vesicle bilayer on the relaxivity of encapsulated Gd. Here, the facile synthesis of a composite MR contrast platform is described; it consists of dendrimer conjugates encapsulated in porous polymersomes. These nanoparticles exhibit improved permeability to water flux and a large capacity to store chelated Gd within the aqueous lumen, resulting in enhanced longitudinal relaxivity. The porous polymersomes, ,130,nm in diameter, are produced through the aqueous assembly of the polymers, polyethylene oxide- b -polybutadiene (PBdEO), and polyethylene oxide- b -polycaprolactone (PEOCL). Subsequent hydrolysis of the caprolactone (CL) block resulted in a highly permeable outer membrane. To prevent the leakage of small Gd-chelate through the pores, Gd was conjugated to polyamidoamine (PAMAM) dendrimers via diethylenetriaminepentaacetic acid dianhydride (DTPA dianhydride) prior to encapsulation. As a result of the slower rotational correlation time of Gd-labeled dendrimers, the porous outer membrane of the nanovesicle, and the high Gd payload, these functional nanoparticles are found to exhibit a relaxivity (R1) of 292 109,mM,1,s,1 per particle. The polymersomes are also found to exhibit unique pharmacokinetics with a circulation half-life of >3.5,h and predominantly renal clearance. [source]

Conductive Core,Sheath Nanofibers and Their Potential Application in Neural Tissue Engineering

Jingwei Xie
Abstract Conductive core,sheath nanofibers are prepared by a combination of electrospinning and aqueous polymerization. Specifically, nanofibers electrospun from poly(, -caprolactone) (PCL) and poly(L -lactide) (PLA) are employed as templates to generate uniform sheaths of polypyrrole (PPy) by in-situ polymerization. These conductive core,sheath nanofibers offer a unique system to study the synergistic effect of different cues on neurite outgrowth in vitro. It is found that explanted dorsal root ganglia (DRG) adhere well to the conductive core,sheath nanofibers and generate neurites across the surface when there is a nerve growth factor in the medium. Furthermore, the neurites can be oriented along one direction and enhanced by 82% in terms of maximum length when uniaxially aligned conductive core,sheath nanofibers are compared with their random counterparts. Electrical stimulation, when applied through the mats of conductive core,sheath nanofibers, is found to further increase the maximum length of neurites for random and aligned samples by 83% and 47%, respectively, relative to the controls without electrical stimulation. Together these results suggest the potential use of the conductive core,sheath nanofibers as scaffolds in applications such as neural tissue engineering. [source]

pH-Responsive Flower-Type Micelles Formed by a Biotinylated Poly(2-vinylpyridine)- block -poly(ethylene oxide)- block -poly(, -caprolactone) Triblock Copolymer

Kathy Van Butsele
Abstract In the present work, a method is proposed to assemble pH-responsive, flower-like micelles that can expose a targeting unit at their periphery upon a decrease in pH. The micelles are composed of a novel biotinylated triblock copolymer of poly(,, -caprolactone)- block -poly(ethylene oxide)- block -poly(2-vinylpyridine) (PCL- b -PEO- b -P2VP) and the non-biotinylated analogue. The block copolymers are synthesized by sequential anionic and ring-opening polymerization. The pH-dependent micellization behaviour in aqueous solution of the triblock copolymers developed is studied using dynamic light scattering, zeta potential, transmission electron microscopy (TEM), and fluorimetric measurements. The shielding of the biotin at neutral pH and their availability at the micelle surface upon protonation is established by TEM and surface plasmon resonance with avidin and streptavidin-coated gold surfaces. The preliminary stealthy behavior of these pH-responsive micelles is examined using the complement activation (CH50) test. [source]

One-Step Process for Creating Triple-Shape Capability of AB Polymer Networks

Marc Behl
Abstract Triple-shape polymers can move from a first shape (A) to a second shape (B) and from there to a third shape (C), where both shape changes are induced by temperature increases. This triple-shape capability is obtained for multiphase polymer networks after application of a complex thermomechanical programming process, which consists of two steps; these steps create shapes (B) and (A), while shape (C) is defined by the covalent crosslinks of the polymer network. Here, the creation of the triple-shape capability for an AB polymer network system by a simple one-step process similar to a conventional dual-shape programming process is reported. The polymer networks are based on poly(, -caprolactone) (PCL) and poly(cyclohexyl methacrylate); favorable compositions for obtaining a triple shape effect have a PCL content between 35 and 60 wt%. This finding substantially facilitates handling of the triple-shape technology and is an important step toward the realization of potential applications in which more than one shape change is required. [source]

Poly(,-caprolactone)-Functionalized Carbon Nanotubes and Their Biodegradation Properties,

H.-L. Zeng
Abstract Biodegradable poly(,-caprolactone) (PCL) has been covalently grafted onto the surfaces of multiwalled carbon nanotubes (MWNTs) by the "grafting from" approach based on in-situ ring-opening polymerization of ,-caprolactone. The grafted PCL content can be controlled easily by adjusting the feed ratio of monomer to MWNT-supported macroinitiators (MWNT-OH). The resulting products have been characterized with Fourier-transform IR (FTIR), NMR, and Raman spectroscopies, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). After PCL was coated onto MWNT surfaces, core/shell structures with nanotubes as the "hard" core and the hairy polymer layer as the "soft" shell are formed, especially for MWNTs coated with a high density of polymer chains. Such a polymer shell promises good solubility/dispersibility of the MWNT,PCL nanohybrids in low-boiling-point organic solvents such as chloroform and tetrahydrofuran. Biodegradation experiments have shown that the PCL grafted onto MWNTs can be completely enzymatically degraded within 4,days in a phosphate buffer solution in the presence of pseudomonas (PS) lipase, and the carbon nanotubes retain their tubelike morphologies, as observed by SEM and TEM. The results present possible applications for these biocompatible PCL-functionalized CNTs in bionanomaterials, biomedicine, and artificial bones. [source]

A Novel Route to Thermosensitive Polymeric Core,Shell Aggregates and Hollow Spheres in Aqueous Media,

Y. Zhang
Abstract Poly(,-caprolactone)/poly(N -isopropylacrylamide) (PCL/PNIPAM) core,shell particles are obtained by localizing the polymerization of NIPAM and crosslinker methylene bisacrylamide around the surface of PCL nanoparticles. The resultant particles are converted to hollow PNIPAM spheres by simply degrading the PCL core with an enzyme. The hollow spheres are thermosensitive and display a reversible swelling and de-swelling at ,,32,C. [source]

Magnetite-Loaded Polymeric Micelles as Ultrasensitive Magnetic-Resonance Probes,

H. Ai
Increased contrast in magnetic resonance imaging (MRI) is accomplished using polymeric micelles loaded with superparamagnetic iron oxide (SPIO) nanoparticles encapsulated in biocompatible, biodegradable poly(,-caprolactone)- b -poly(ethylene glycol) (PCL- b -PEG) copolymers (see Figure). The loaded micelles show significantly improved T2 relaxivities and remarkable MRI detection sensitivity. [source]

Evaluation of numerical simulation methods in reactive extrusion

Linjie Zhu
Abstract Reactive extrusion is a complex process, and numerical simulation is an important method in optimizing operational parameters. In the current work, two different simulation methods, one-dimensional (1D) model and three-dimensional (3D) model, were introduced to predict the polymerization of ,-caprolactone in fully filled screw elements. The predicted results of polymerization progression under different simulation conditions based on these two methods were compared. The simulation results show that the simplifications and assumptions in 1D model make it difficult to capture the complex mixing mechanism, heat generation, and heat loss in reactive extrusion. 1D model is feasible only under particular conditions, such as low screw rotating speed, small heat from reaction, and small screw diameter, whereas 3D model is a more powerful simulation tool for much wider processing conditions. 2005 Wiley Periodicals, Inc. Adv Polym Techn 24: 183,193, 2005; Published online in Wiley InterScience ( DOI 10.1002/adv.20041 [source]

Synchrotron X-ray reflectivity studies of nanoporous organosilicate thin films with low dielectric constants

Weontae Oh
Quantitative, non-destructive X-ray reflectivity analysis using synchrotron radiation sources was successfully performed on nanoporous dielectric thin films prepared by thermal processing of blend films of a thermally curable polymethylsilsesquioxane dielectric precursor and a thermally labile triethoxysilyl-terminated six-arm poly(,-caprolactone) porogen in various compositions. In addition, thermogravimetric analysis and transmission electron microscopy analysis were carried out. These measurements provided important structural information about the nanoporous films. The thermal process used in this study was found to cause the porogen molecules to undergo efficiently sacrificial thermal degradation, generating closed, spherical nanopores in the dielectric film. The resultant nanoporous films exhibited a homogeneous, well defined structure with a thin skin layer and low surface roughness. In particular, no skin layer was formed in the porous film imprinted using a porogen loading of 30,wt%. The film porosities ranged from 0 to 33.8% over the porogen loading range of 0,30,wt%. [source]

Synthesis and characterization of temperature-sensitive block copolymers from poly(N -isopropylacrylamide) and 4-methyl-,-caprolactone or 4-phenyl-,-caprolactone

Ren-Shen Lee
Abstract This study synthesizes thermally sensitive block copolymers poly(N -isopropylacrylamide)- b -poly(4-methyl-,-caprolactone) (PNIPA- b -PMCL) and poly(N -isopropylacrylamide)- b -poly(4-phenyl-,-caprolactone) (PNIPA- b -PBCL) by ring-opening polymerization of 4-methyl-,-caprolactone (MCL) or 4-phenyl-,-caprolactone (BCL) initiated from hydroxy-terminated poly(N -isopropylacrylamide) (PNIPA) as the macroinitiator in the presence of SnOct2 as the catalyst. This research prepares a PNIPA bearing a single terminal hydroxyl group by telomerization using 2-hydroxyethanethiol (ME) as a chain-transfer agent. These copolymers are characterized by differential scanning calorimetry (DSC), 1H-NMR, FTIR, and gel permeation chromatography (GPC). The thermal properties (Tg) of diblock copolymers depend on polymer compositions. Incorporating larger amount of MCL or BCL into the macromolecular backbone decreases Tg. Their solutions show transparent below a lower critical solution temperature (LCST) and opaque above the LCST. LCST values for the PNIPA- b -PMCL aqueous solution were observed to shift to lower temperature than that for PNIPA homopolymers. This work investigates their micellar characteristics in the aqueous phase by fluorescence spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). The block copolymers formed micelles in the aqueous phase with critical micelle concentrations (CMCs) in the range of 0.29,2.74 mg L,1, depending on polymer compositions, which dramatically affect micelle shape. Drug entrapment efficiency and drug loading content of micelles depend on block polymer compositions. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Modification of cellulose acetate with oligomeric polycaprolactone by reactive processing: Efficiency, compatibility, and properties

Szilvia Klbert
Abstract Oligomeric polycaprolactone (oPCL) was used for the modification of cellulose acetate by reactive processing in an internal mixer at 180C, 50 rpm, 60 min reaction time, and 45 wt % caprolactone (CL) content. The product of the reaction was characterized by several analytical techniques and its mechanical properties were determined by dynamic mechanical thermal analysis and tensile testing. The synthesized oPCL contained small and large molecular weight components. The small molecular weight fraction plasticized cellulose acetate externally and helped fusion. Although composition and structure did not differ considerably from each other when CL monomer or polycaprolactone oligomer was used for modification, the grafting of a few long chains had considerable effect on some properties of the product. The large molecular weight chains attached to CA increased the viscosity of the melt considerably and resulted in larger deformability. oPCL homopolymer is not miscible with cellulose acetate and migrates to the surface of the polymer. Exuded polycaprolactone oligomers crystallize on the surface but can be removed very easily. More intense conditions may favor the grafting of long chains leading to polymers with advantageous properties. 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]

Linear-dendritic copolymers as nanocatalysts

M. Adeli
Abstract Functionalized poly(ethylene glycol) (PEG) containing four chloride end functional groups (PEG-Cl4) was synthesized through reaction between cyanuric chloride and PEG-(OH)2. Chloride end functional groups of PEG-Cl4 were able to initiate the ring opening polymerization of 2-ethyl-2-oxazoline and star copolymers containing a PEG core, and poly(2-ethyl-2-oxazoline) (POX) arms were obtained. Polymerization was quenched using diethanolamine, and star copolymers containing hydroxyl end functional groups (PEG-POX-OH) were obtained. ,-Caprolactone was then polymerized using the hydroxyl end functional groups of star copolymers and amphiphilic linear-dendritic copolymers containing PEG and POX, and poly(caprolactone) (PCL) blocks were synthesized. Linear-dendritic copolymers were able to load the organic and inorganic guest molecules. Application of host-guest systems such as nanocatalyst for Heck chemical reaction was also investigated. 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]

Surface modification of starch nanocrystals through ring-opening polymerization of ,-caprolactone and investigation of their microstructures

Hassan Namazi
Abstract Bionanoparticles of starch obtained by submitting native potato starch granules to acid hydrolysis conditions. The resulted starch nanoparticles were used as core or macro initiator for polymerization of ,-caprolactone (CL). Starch nanoparticle- g -polycaprolactone was synthesized through ring-opening polymerization (ROP) of CL in the presence of Sn(Oct)2 as initiator. The detailed microstructure of the resulted copolymer was characterized with NMR spectroscopy. Thermal characteristic of the copolymer was investigated using DSC and TGA. By introducing PCL, the range of melting temperature for starch was increased and degradation of copolymer occurred in a broader region. X-ray diffraction and TEM micrographs confirmed that there was no alteration of starch crystalline structure and morphology of nanoparticles, respectively. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Studies on thermoplastic polyurethanes based on new diphenylethane-derivative diols.


Abstract Two series of poly(ether urethane)s and one series of poly(ester urethane)s were synthesized, containing, respectively, poly(oxytetramethylene) diol (PTMO) of Mn = 1000 and 2000 and poly(,-caprolactone) diol of Mn = 2000 as soft segments. In each series the same hard segment, i.e., 4,4,-(ethane-1,2-diyl)bis(benzenethiohexanol)/hexane-1,6-diyl diisocyanate, with different content (, 14,72 wt %) was used. The polymers were prepared by a one-step melt polymerization in the presence of dibutyltin dilaurate as a catalyst, at the molar ratio of NCO/OH = 1 (in the case of the polymers from PTMO of Mn = 1000 also at 1.05). For all polymers structures (by FTIR and X-ray diffraction analysis) and physicochemical, thermal (by differential scanning calorimetry and thermogravimetric analysis), and tensile properties as well as Shore A/D hardness were determined. The resulting polymers were thermoplastic materials with partially crystalline structures (except the polymer with the highest content of PTMO of Mn = 2000). It was found that the poly(ether urethane)s showed lower crystallinity, glass-transition temperature (Tg), and hardness as well as better thermal stability than the poly(ester urethane)s. Poly(ether urethane)s also exhibited higher tensile strength (up to 23.5 MPa vs. 20.3 MPa) and elongation at break (up to , 1950% vs. 1200%) in comparison with the corresponding poly(ester urethane)s. Among the poly(ether urethane)s an increase in soft-segment length was accompanied by an increase in thermal stability, tensile strength, and elongation at break, as well as a decrease in Tg, crystallinity, and hardness. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Thermal stability and molecular interaction of polyurethane nanocomposites prepared by in situ polymerization with functionalized multiwalled carbon nanotubes

R. N. Jana
Abstract Polyurethane (PU) nanocomposites were prepared through conventional and in situ methods with multiwalled carbon nanotubes (MWNTs) functionalized with poly(,-caprolactone). The thermal degradation and stability of PU,MWNT nanocomposites were investigated with nonisothermal thermogravimetry and were explained in terms of the interaction between MWNTs and PU molecules with Fourier transform infrared spectroscopy. The difference in thermal stability between the conventional and in situ nanocomposites was also compared. The thermal degradation of all the nanocomposite samples took place in two stages and followed a first-order reaction. The degradation temperature of the in situ nanocomposites was higher than that of the conventional nanocomposites with the same loading of MWNTs. The activation energy at 10% degradation and the half-life period were also higher in the in situ nanocomposites compared to the conventional nanocomposites. Such higher thermal stability of the in situ nanocomposites was ascribed to covalent bond formation between MWNTs and PU chains, which could result in better dispersion of MWNTs in the PU matrix for the in situ nanocomposites than for the conventional nanocomposites. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Water absorption properties of phosphate glass fiber-reinforced poly-,-caprolactone composites for craniofacial bone repair

Levent Onal
Abstract The moisture uptake of polymers and composites has increasing significance where these materials are specified for invasive, long-term medical applications. Here we analyze mass gain and the ensuing degradation mechanisms in phosphate glass fiber reinforced poly-,-caprolactone laminates. Specimens were manufactured using in situ polymerization of ,-caprolactone around a bed of phosphate glass fibers. The latter were sized with 3-aminopropyltriethoxysilane to control the rate of modulus degradation. Fiber content was the main variable in the study, and it was found that the moisture diffusion coefficient increased significantly with increasing fiber volume fraction. Diffusion, plasticization, and leaching of constituents appear to be the dominant aspects of the process over these short-term tests. 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source]

Synthesis and characterization of fullerene grafted poly(,-caprolactone)

Weihua Kai
Abstract The fullerene grafted poly(,-caprolactone) (PCL) was successfully synthesized with a graft efficiency of 80%. The fullerene moieties grafted onto the PCL chain aggregate into 1,2 ,m particles so that a physical pseudo -network is formed. Because of the existence of the network structure, the fullerene grafted PCL film can retain its shape at much higher temperatures than that of pure PCL film, as observed in dynamic mechanical tests. It shows a hydrophobic gelling behavior in chloroform solution. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Comparative study of the hydrolytic degradation of glycolide/L -lactide/,-caprolactone terpolymers initiated by zirconium(IV) acetylacetonate or stannous octoate

Janusz Kasperczyk
Abstract A series of copolymers have been synthesized by the ring-opening polymerization of glycolide, L -lactide, and ,-caprolactone with zirconium(IV) acetylacetonate [Zr(Acac)4] or stannous octoate [Sn(Oct)2] as the catalyst. The resulting terpolymers have been characterized by analytical techniques such as proton nuclear magnetic resonance, size exclusion chromatography, and differential scanning calorimetry. Data have confirmed that Sn(Oct)2 leads to less transesterification of polymer chains than Zr(Acac)4 under similar conditions. The various copolymers have been compression-molded and allowed to degrade in a pH 7.4 phosphate buffer at 37C. The results show that the degradation rate depends not only on the copolymer composition but also on the chain microstructure, the Sn(Oct)2 -initiated copolymers degrading less rapidly than Zr(Acac)4 -initiated ones with more random chain structures. The caproyl component appears the most resistant to degradation as its content increases in almost all cases. Moreover, caproyl units exhibit a protecting effect on neighboring lactyl or glycolyl units. The glycolyl content exhibits different features: it decreases because of faster degradation of glycolyl units, which are more hydrophilic than caproyl and lactyl ones, remains stable in the case of abundant CGC sequences, which are very resistant to degradation, or even increases because of the formation of polyglycolide crystallites. Terpolymers can crystallize during degradation if the block length of one of the components is sufficiently long, even though they are amorphous initially. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Effective preparation and characterization of montmorillonite/poly(,-caprolactone)-based polyurethane nanocomposites

Eun Hwan Jeong
Abstract In this study, montmorillonite (MMT)/poly(,-caprolactone)-based polyurethane cationomer (MMT/PCL-PUC) nanocomposites were prepared and their mechanical properties, thermal stability, and biodegradability were investigated. PCL-PUC has 3 mol % of quaternary ammonium groups in the main chain. The MMT was successfully exfoliated and well dispersed in the PCL-PUC matrix for up to 7 wt % of MMT. The 3 mol % of quaternary ammonium groups facilitated exfoliation of MMT. The 1 wt % MMT/PCL-PUC nanocomposites showed enhanced tensile properties relative to the pure PCL-PU. As the MMT content increased in the MMT/PCL-PUC nanocomposites, the degree of microphase separation of PCL-PUC decreased because of the strong interactions between the PCL-PUC chains and the exfoliated MMT layers. This resulted in an increase in the Young's modulus and a decrease in the elongation at break and maximum stress of the MMT/PCL-PUC nanocomposites. Biodegradability of the MMT/PCL-PUC nanocomposites was dramatically increased with increasing content of MMT, likely because of the less phase-separated morphology of MMT/PCL-PUC. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Biodegradable poly(vinyl alcohol)- graft - poly(,-caprolactone) comb-like polyester: Microwave synthesis and its characterization

Zhaoju Yu
Abstract Poly(vinyl alcohol)-initiated microwave-assisted ring opening polymerization of ,-caprolactone in bulk was investigated, and a series of poly(vinyl alcohol)- graft -poly(,-caprolactone) (PVA- g -PCL) copolymers were prepared, with the degree of polymerization (DP) of PCL side chains and the degree of substitution (DS) of PVA by PCL being in the range of 3,24 and 0.35,0.89, respectively. The resultant comb-like PVA- g -PCL copolymers were confirmed by means of FTIR, 1H NMR, and viscometry measurement. The introduction of hydrophilic backbone resulted in the decrease in both melting point and crystallization property of the PVA- g -PCL copolymers comparing with linear PCL. With higher microwave power, the DP of PCL side chains and DS of PVA backbone were higher, and the polymerization reaction proceeded more rapidly. Both the DP and monomer conversion increased with irradiation time, while the DS increased first and then remained constant. With initiator in low concentration, the DP and DS were higher, while the monomer was converted more slowly. Microwaves dramatically improved the polymerization reaction in comparison of conventional heating method. 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104, 3973,3979, 2007 [source]

Characterization of pegylated copolymeric micelles and in vivo pharmacokinetics and biodistribution studies

Wen-Jen Lin
Abstract The aim of this study was to evaluate the influence of pegylated copolymeric micelle carrier on the biodistribution of drug in rats. The copolymers were synthesized via a modified ring-opening copolymerization of lactone monomers (,-caprolactone, ,-valerolactone, L -lactide) and poly(ethylene glycol) (PEG10,000 and PEG4000). The molecular weights and the polydispersities of synthesized copolymers were in the range of 15,000,31,000 g/mol and 1.7,2.7, respectively. All of the pegylated amphiphilic copolymers were micelles formed with low CMC values in the range of 10,7,10,8M. The drug-loaded micelles were prepared via a dialysis method. The average particle size of micelles was around 150,200 nm. The cytotoxicity in terms of cell viability after treated with PCL,PEG, PVL,PEG, and PLA,PEG micelles was insignificant. PCL,PEG and PVL,PEG micelles without branch side chain in structures had higher drug loading than PLA,PEG micelles. In vitro release profiles indicated the release of indomethacin from these micelles exhibited a sustained release behavior. The similar phenomenon was also observed in vivo in rats. The pegylated copolymeric micelles not only decreased drug uptake by the liver and kidney, but also prolonged drug retention in the blood. 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source]