Different ways for grafting ester derivatives of poly(ethylene glycol) onto chitosan: related characteristics and potential properties

The grafting of poly(ethylene glycol) functionalized by ester groups (MeO-PEG-ester) onto chitosan was studied and optimized using different reaction conditions. In a first procedure, the grafting was made from 6-O-triphenylmethyl-chitosan after protection of primary hydroxyl groups and in a second one, it was made directly onto chitosan. NMR spectroscopy was an important tool to study these reactions and the grafting is unequivocally showed up. Moreover, for each procedure, the solubility and surface properties of the obtained copolymers were evaluated and compared.     

Surface and mechanical properties of microporous membranes of poly(ethylene glycol)-polydimethylsiloxane copolymer/chitosan

Poly(ethylene glycol)-polydimethylsiloxane (PEG-PDMS) block copolymers were prepared via a condensation reaction between PEG diacid and PDMS diol. PEG diacid was synthesized from the reaction between hydroxy-terminated PEG and succinic anhydride. PDMS diol was prepared from the ring-opening polymerization of octamethylcyclotetrasiloxane (D₄) followed by hydrosilylation with allyl alcohol. The copolymers were incorporated into chitosan in order that good water swellability and wettability of chitosan were retained due to hydrophilic PEG blocks, whereas PDMS block in the copolymers functioned as a toughening modifier. Percent crosslinking of 66-84 was observed once 5-10 wt% of the copolymers was incorporated. As compared to the unmodified sample, the copolymer-containing chitosan exhibited the decreases in both water contact angles and the rate of water vapor permeability. The studies on tensile properties indicated that incorporation of copolymers into chitosan improved the flexibility of the films.     

Precise preparation of four-arm-poly(ethylene glycol)-block-poly(trimethylene carbonate) star block copolymers via activated monomer mechanism and examination of their solution properties

The polymerization of trimethylene carbonate (TMC) in the presence of HCl·Et₂O via activated monomer mechanism was performed to synthesize 4a-PEG-b-PTMC star block copolymers composed of poly(ethylene glycol) (PEG) and poly(trimethylene carbonate) (PTMC) using four-arm (4a) PEG as an initiator. The TMC conversion and molecular weight of PTMC increased linearly with the polymerization time or the feed ratios of the TMC to 4a-PEG in the presence of HCl·Et₂O in CH₂Cl₂ at 25 °C. The obtained PTMC had molecular weights close to the theoretical value calculated from TMC to PEG molar ratio and exhibited monomodal GPC curve. We prepared successfully 4a-PEG-b-PTMC star block copolymers without metal catalyst at room temperature via living ring-opening polymerization (ROP) of TMC from 4a-PEG as an initiator in the presence of HCl·Et₂O as a monomer activator. The CMCs of the 4a-PEG-b-PTMC star block copolymers determined from fluorescence measurements. The CMCs of the 4a-PEG-b-PTMC star block copolymers decreased in the order of the increase in the PTMC segment. The partition equilibrium constant, K_v, which is an indicator of the hydrophobicity of the micelles of the 4a-PEG-b-PTMC star block copolymers in aqueous media, increased with the increase in the PTMC segment. In conclusion, we confirmed that the 4a-PEG-b-PTMC star block copolymers form micelles and hence may be potential hydrophobic-drug delivery vehicles.     

One-pot synthesis of poly(triazole-graft-caprolactone) via ring-opening polymerization combined with click chemistry as a novel strategy for graft copolymers

The one-pot construction of polytriazole grafted with poly(ε-caprolactone) via the polymerization of 4-azido-1-(prop-2-yn-1-yloxy)butan-2-ol (N₃hydroxypropargyl) and ε-caprolactone monomers is reported. For this purpose, a click reaction and ring-opening polymerization (ROP) were combined and carried out simultaneously. N₃hydroxypropargyl served as both the ROP initiator and a monomer for the click polymerization. Thus, an in situ “grafting-through and from” strategy was established in one pot. CuBr and Sn(Oct)₂ were utilized as dual catalysts, and the polymerization reactions were carried out at 120 °C under a N₂ atmosphere.     

Miscibility of chitosan/poly(ethylene oxide) blends and effect of doping alkali and alkali earth metal ions on chitosan/PEO interaction

The miscibility of Chitosan (CS) and poly(ethylene oxide) (PEO) in their blends and the effect of K⁺ and Ca²⁺ doping on the CS/PEO interaction have been investigated in this work. CS and PEO appeared to be miscible and the DSC analysis suggested the Flory-Huggins interaction parameter χ_AB to be −0.21. Doping of K⁺ and Ca²⁺ into the CS/PEO blend matrix enhanced the cooperative interaction between CS and PEO and this enhancement was larger for Ca²⁺ than for K⁺. The difference between Ca²⁺ and K⁺ possibly reflects a stronger multi-valence interaction of Ca²⁺ with the amino and hydroxyl groups of CS as well as the ether groups of PEO to form a stable CS/Ca²⁺/PEO complex and a less significant interaction of K⁺, as suggested by DSC, WAXD and FTIR results. MD simulations clearly indicated the correlation between the dynamic behavior and the interaction of K⁺ and Ca²⁺ in the CS/PEO blend matrix.     

Synthesis, characterization and properties of chitosan modified with poly(ethylene glycol)-polydimethylsiloxane amphiphilic block copolymers

Synthesis of poly(ethylene glycol)-polydimethylsiloxane amphiphilic block copolymers is discussed herein. Siloxane prepolymer was first prepared via acid-catalyzed ring-opening polymerization of octamethylcyclotetrasiloxane (D₄) to form polydimethylsiloxane (PDMS) prepolymers. It was subsequently functionalized with hydroxy functional groups at both terminals. The hydroxy-terminated PDMS can readily react with acid-terminated poly(ethylene glycol) (PEG diacid) to give PEG-PDMS block copolymers without using any solvent. The PEG diacid was prepared from hydroxy-terminated PEG through the ring-opening reaction of succinic anhydride. Their chemical structures and molecular weights were characterized using ¹H NMR, FTIR and GPC, and thermal properties were determined by DSC. The PEG-PDMS copolymer was incorporated into chitosan in order that PDMS provided surface modification and PEG provided good water swelling properties to chitosan. Critical surface energy and swelling behavior of the modified chitosan as a function of the copolymer compositions and contents were investigated.     

Amphiphilic chitosan graft copolymer via combination of ROP, ATRP and click chemistry: Synthesis, self-assembly, thermosensitivity, fluorescence, and controlled drug release

Novel amphiphilic chitosan-g-poly(ε-caprolactone)-(g-poly(2-(2-methoxyethoxy)ethyl methacrylate)-co-oligo(ethylene glycol) methacrylate) (CS-g-PCL(-g-P(MEO₂MA-co-OEGMA))) copolymers with double side chains of PCL and P(MEO₂MA-co-OEGMA) were synthesized via combination of ring-opening polymerization (ROP), atom transfer radical polymerization (ATRP) and click chemistry. The molar ratio of PCL and P(MEO₂MA-co-OEGMA) was varied through variation of the feed ratio and the coupling efficiency of click chemistry is comparatively high. The graft copolymers can assemble into spherical micelles. The micelles show thermosensitive properties and the lower critical solution temperatures (LCSTs) were influenced by CS chains and the ratio of PCL and P(MEO₂MA-co-OEGMA) side chains. Moreover, the micelles can reversibly swell and shrink in response to the change of temperatures. Furthermore, the micelles present obvious fluorescence and the fluorescent intensity can be adjusted by altering the temperatures. The investigation of doxorubicin release from the micelles indicated that the release rate of the drug could be effectively controlled by altering the temperatures.     

Comments to the paper “The need to reconsider tradional free volume theory for polymer electrolytes”

The specific free volume V_f is calculated from the Simha–Somcynsky equation (S–S eos) of state analysis of pressure–volume–temperature (PVT) data of Bendler et al. [Electrochim. Acta 48 (2003) 2267], for poly(propylene glycol) (PPG) containing LiCF₃SO₃. We found that, due to the compressibility of the occupied volume, V_f is not constant for a constant specific total volume V but depends on the pathway in the P–T plane on which the V is reached. From this it follows that the observation of different relaxation properties for the same total volume in variable temperature, high-pressure experiments does not necessarily contradict the free volume theory. We show that the traditional free volume theory is consistent with the electrical conductivity data for Bendler et al. for 20:1 PPG:LiCF₃SO₃ when V_f is calculated from the S–S eos. Moreover, we derive an empirical function for describing the temperature and pressure dependence of the electrical conductivity which contains, beside the three parameters of the Vogel–Tammann–Fulcher law, only two additional parameters, both control the effect of pressure on the electrical conductivity.     

Synthesis and characterization of well-defined poly(l-lactide) functionalized graphene oxide sheets with high grafting ratio prepared through click chemistry and supramolecular interactions

Two simple and effective methods, “click” chemistry and supramolecular interactions, are demonstrated here to synthesize well-defined poly(l-lactide) (PLLA) functionalized graphene oxide (GO) sheets. We provide a simple method to introduce azide groups on GO sheets by the ring opening reaction of sodium azide with the epoxide groups of GO. The GO-N₃ sheets can easily undergo “click” reaction with alkyne-terminated PLLA by “grafting onto” method to produce GO/PLLA composites with high grafting ratio and exfoliated structure. Interestingly, GO-N₃ can be grafted with oxygen-containing polymers such as PLLA, polymethyl methacrylate (PMMA) or polyethylene oxide (PEO) via supramolecular interactions between the azide groups and these oxygen atoms on polymers, producing GO/polymer composites with low grafting ratio and intercalated structure. These “grafting onto” methods are useful to produce a variety of GO/polymer composites with different structure via “click” reaction or supramolecular interactions, which have potential applications in material science.     

Toward “Rubbery” nanoparticles

The synthesis of electrically Conducting Natural Rubber (CNR) nanoparticles from natural rubber (cis 1, 4 polyisoprene) by a simple chemical doping technique is reported for the first time. Much before the establishment of conjugation as a precondition for polymers to be conducting a typical nonconjugated polymer like cis 1,4 polyisoprene was shown to develop intrinsic conductivity on doping. However, the possibility of developing conducting nanoparticles of natural rubber by doping has never been explored. Doping of natural rubber solution with Antimony pentchloride is found to lead to the formation of nanosized rubber particles with improved thermal stability and lower degradation characteristics than that of pristine rubber. Transmission electron microscopy and Dynamic Light Scattering experiments revealed a highly uniform dispersion of the particles with sizes in the range of 4 nm. The doped nanoparticles are found to retain “rubbery” properties of natural rubber and therefore these can be rightly termed as Rubber Nano particles. The development of nanoparticles of rubber assumes great significance in that it would lead to hitherto unknown applications for natural rubber in micro applications‐like sensors, and optoelectronics devices to macro applications such as compatible reinforcing fillers for elastomers and plastics to replace conventional fillers like carbon particles. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and characterization of lactobionic acid grafted pegylated chitosan and nanoparticle complex application

A series of chemical modifications of chitosan were conducted by grafting a hydrophilic methoxy poly(ethylene glycol) (MPEG) and a target sugar molecule lactobionic acid (LA). The MPEG was grafted onto C6-OH position of chitosan, and the grafting degree was reduced for chitosan with high degree of depolymerization. The lactobionic acid was proposed to graft onto C2-NH₂ position of chitosan. The LA grafting ratio was dependent on pegylation degree of chitosan, where the flexibility and shielding effect of MPEG hindered LA grafting onto chitosan. The lactobionic acid grafted pegylated chitosan, DADP-CS-(O-MPEG)-(N-LA), successfully provoked DNA condensation into nanoparticle complexes due to electrostatic compaction. The presence of MPEG on DADP-CS-(O-MPEG)-(N-LA) played an important role on preventing nanoparticle aggregation.     

Temperature and pH sensitive hydrogels composed of chitosan and poly(ethylene glycol)

Summary Chitosan based semi-interpenetrating polymer network (semi-IPN) hydrogels containing different amounts of poly(ethylene glycol) (PEG) were prepared. The crosslinking of the hydrogels was achieved by using a naturally occurring nontoxic cross-linking agent genipin. The swelling behaviour of these hydrogels was studied by immersing the films in deionized water at 25, 37 and 45 °C and in media of different pHs at 37 °C. Swelling was found to be dependent on temperature, pH of the medium and the amount of PEG in the gel. States of water in the hydrogels swollen in deionized water at 37 °C were determined using Differential Scanning Calorimetry (DSC). The equilibrium water content and the amount of freezing water in the swollen hydrogels increased with the increase in PEG concentration in the gels.     

Time-resolved gel permeation chromatographic study on poly(N-isopropylacrylamide)-block-poly(ethylene glycol) prepared by soap-free emulsion polymerization

To synthesize an amphiphilic block copolymer of poly(N-isopropylacrylamide)-block-poly(ethylene glycol) (NE), an aqueous soap-free emulsion polymerization system was employed where poly(N-isopropylacrylamide) (PNIPA), polymerized from the radically activated chain ends of poly(ethylene glycol) (PEG), forms micelle cores stabilized by PEG brush chains emanating there from. When this polymerization was carried out at temperatures equal to or higher than 34 °C, narrowly-dispersed NE, which cannot be obtained by solution polymerization, was successfully obtained. To elucidate the living nature of the soap-free emulsion polymerization, time-dependent monomer conversion and molecular weight of NE was investigated by time-resolved gel permeation chromatography (GPC). The results indicate that the compartmentalization of end radicals into micelles cores leads to the quasi-living behavior of the polymerization.     

Acrylonitrile-based copolymer membranes containing reactive groups: effects of surface-immobilized poly(ethylene glycol)s on anti-fouling properties and blood compatibility

The anti-fouling properties and blood compatibility of poly(acrylonitrile-co-maleic acid) (PANCMA) membranes were improved by the immobilization of poly(ethylene glycol)s (PEG) on membrane surface. It was found that the reactive carboxyl groups on PANCMA membrane surface could be conveniently conversed into anhydride groups and then esterified with PEG. Chemical and morphological changes as well as biocompatibility on membrane surface were analyzed by Fourier transform infrared spectroscopy, elemental analysis, scanning electron microscopy, water contact angle, protein adsorption, and platelet adhesion. Results revealed that, with the immobilization of PEG, the hydrophilicity and blood compatibility of the acrylonitrile-based copolymer membranes were improved obviously. The molecular weight of PEG had an obvious influence on the properties of the PEG-immobilized membranes. Permeation behaviors for the studied membranes were investigated by water and bovine serum albumin (BSA) filtration experiments. Compared with the original PANCMA membrane, the membrane immobilized with PEG 400 (M_w=400 g/mol) showed a three-fold increase in a BSA solution flux, a 40.4% reduction in total fouling, and a 57.9% decrease in BSA adsorption.     

Synthesis and properties of ABA-type triblock copolymers of poly(glycolide-co-caprolactone) (A) and poly(ethylene glycol) (B)

Poly(glycolide-co-caprolactone) (A)-poly(ethylene glycol) (B) ABA-type triblock copolymers (PGCE) were synthesized by bulk ring opening polymerization, using the hydroxyl endgroups of poly(ethylene glycol) (PEG) as initiator and stannous octoate as catalyst. The resulting copolymers were characterized by various analytical techniques. Gel permeation chromatographic analysis indicated that the polymerization product was free of residual monomers, PEG and oligomers. ¹H NMR and differential scanning calorimeter results demonstrated that the copolymers had a structure of poly(glycolide-co-caprolactone) (PGC) chains chemically attached to PEG segments. All the PGCE copolymers showed improved hydrophilicity in comparison with the corresponding PGC copolymers with the same molar ratio of glycolidyl and caproyl units. The microspheres of PGCE copolymer exhibited rough surfaces quite different from the smooth surface of PGC microspheres. This phenomenon was attentively ascribed to the highly swollen ability of PGCE copolymers and the freeze-drying process in the microspheres fabrication.     

Crystallization behavior of “wet brush” and “dry brush” blends of PS‐b‐PEO‐b‐PS/h‐PEO

The crystallization behavior of the blending system consists of homopolymer poly(ethylene oxide) (h‐PEO) with different molecular weights, and polystyrene‐block‐poly (ethylene oxide)‐block‐polystyrene (PS‐b‐PEO‐b‐PS) triblock copolymer has been investigated by DSC measurements. The crystallization of PEO block (b‐PEO) in block copolymer occurs under much lower temperature than that of the h‐PEO in the bulk (ΔT > 65 °C), which is attributed to the homogeneous nucleation crystallization behavior of the b‐PEO microdomains. In both the “dry‐brush” and the “wet brush” blending systems, the homogeneous nucleation crystallization temperature of PS‐b‐PEO‐b‐PS/h‐PEO blends increases due to the increase of the domain size. The heterogeneous nucleation crystallization temperatures of h‐PEO in the wet brush blending systems are higher than that of the corresponding h‐PEO in the bulk. At the same time, the heterogeneous nucleation crystallization temperature of b‐PEO10000 decreases from 43°C to 30°C and 40°C in the h‐PEO600 and h‐PEO2000 blending systems, respectively, because of the stretching of the PEO chains in the wet brush. However, this kind of phenomenon does not happen in the dry brush blending systems. The self‐seeding procedure was used to further ascertain the nucleation mechanism in the crystallization process. As a result, the self‐seeding domains have been confirmed, and the difference between the dry brush and wet brush systems has been observed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Interrogation of “surface,” “skin,” and “core” orientation in thermotropic liquid‐crystalline copolyester moldings by near‐edge X‐ray absorption fine structure and wide‐angle X‐ray scattering

Injection molding thermotropic liquid‐crystalline polymers (TLCPs) usually results in the fabrication of molded articles that possess complex states of orientation that vary greatly as a function of thickness. “Skin‐core” morphologies are often observed in TLCP moldings. Given that both “core” and “skin” orientation states may often differ both in magnitude and direction, deconvolution of these complex orientation states requires a method to separately characterize molecular orientation in the surface region. A combination of two‐dimensional wide‐angle X‐ray scattering (WAXS) in transmission and near‐edge X‐ray absorption fine structure (NEXAFS) spectroscopy is used to probe the molecular orientation in injection molded plaques fabricated from a 4,4′‐dihydroxy‐α‐methylstilbene (DHαMS)‐based thermotropic liquid crystalline copolyester. Partial electron yield (PEY) mode NEXAFS is a noninvasive ex situ characterization tool with exquisite surface sensitivity that samples to a depth of 2 nm. The effects of plaque geometry and injection molding processing conditions on surface orientation in the regions on‐ and off‐ axis to the centerline of injection molded plaques are presented and discussed. Quantitative comparisons are made between orientation parameters obtained by NEXAFS and those from 2D WAXS in transmission, which are dominated by the microstructure in the skin and core regions. Some qualitative comparisons are also made with 2D WAXS results from the literature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation and characterization of poly(ethylene glycol) crosslinked chitosan films

Poly(ethylene glycol) (PEG) crosslinked chitosan films with various PEG to chitosan ratio and PEG molecular weight were successfully prepared via the epoxy‐amine reaction between chitosan and PEG‐epoxy. The thermal and mechanical properties and swelling behavior were studied for the PEG crosslinked chitosan films. The mechanical strength of chitosan films were greatly enforced by the introduction of PEG‐epoxy, achieving an elongation of about 80%. It was found that the crosslinked chitosan films form hydrogel in water, achieving a swelling ratio higher than 20 times of original weight. The swelling behavior of chitosan films relied greatly on the molecular weight of the crosslinker PEG‐epoxy and the weight percent of PEG‐epoxy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

ELECTROOSMOTIC DEWATERING BY A “NEW” METHOD USING A “GATE” ELECTRODE: FIELD EFFECT TRANSISTOR (FET) MODEL OR SIMPLY A MULTISTAGE DEWATERING?

Recently some workers in the field of electrostatics have proposed a “new” method of electroosmotic dewatering (EOD) in which a third electrode (called the “gate” electrode) is placed between the anode and the cathode to enhance the EOD. These authors present a conceptual analysis in terms of the notions of a field-effect transistor (FET). We show here that the proposed method is simply a variation of the multistage EOD already practiced by the workers in this field. It is further demonstrated that an analysis based on the FET model is not applicable to the phenomena involved in the proposed EOD method.     

Properties and structure of PVP–lignin “blend films”

Blend films of poly (4‐vinylpyridine) and lignin were prepared by the casting method. Their structure and properties were studied by Fourier transform infrared (FTIR), wide‐angle X‐ray diffraction (WXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG), and differential scanning calorimetry (DSC). The IR spectra of the blend films indicated that hydrogen‐bonding interaction occurred between poly (4‐vinylpyridine) and lignin. The glass transition temperature of these blends increased with the increase of lignin content, which indicated that these blends were able to form a miscible phase due to the formation of intermolecular hydrogen bonding between the hydroxyl of lignin and the pyridine ring of poly (4‐vinylpyridine). The thermostability of these blends decreased with the increase of lignin content. Initially, an appreciable increase in the measured tensile strength was achieved with a lignin content of 15%, at which the maximum value of 33.03 MPa tensile strength was reached. At a 10% lignin incorporation level, the blend film exhibited a maximum value of 9.03% strain. When the threshold in lignin content for blend films exceeded that limit of 10% lignin, the strain behavior of these blend films deteriorated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1405–1411, 2005