Microwave-Assisted Synthesis of Poly(ε-caprolactone)-block-poly(ethylene glycol) and Poly(lactide)-block-poly(ethylene glycol)

Summary: This study reported the preparation and characterization of PCL-b-mPEG (poly(ε-caprolactone)-block-poly(ethylene glycol)) and PLL-b-mPEG (poly(L-lactide)-block-poly(ethylene glycol)) diblock copolymers by microwave heating and comparison of resulted products the ones with prepared by conventional heating. Diblock copolymers were synthesized successfully by the microwave-assisted ROP in the presence of stannous octoate (SnOct₂) as catalyst under nitrogen atmosphere in different monomer ratios. Structural and functional characterization of copolymers were performed by FTIR, ¹H-NMR and DSC. Molecular weight values were determined by GPC and also calculated from ¹H-NMR. According to the results, microwave irradiation allowed to obtain polymers with very narrow size distribution in very short reaction time. Similar polymers prepared by conventional heating were also synthesized for comparison. Molecular weight and conversion of polymers were increased by irradiation time. This change was continued until a certain time point after which no more increase was observed. It was concluded that microwave irradiation is a succesful method to obtain these diblock copolymers in very short reaction time and with a similar conversion obtained by conventional method.     

Pyrolysis kinetics of ethylene–propylene (EPM) and ethylene–propylene–diene (EPDM)

The thermal degradation kinetics of several ethylene–propylene copolymers (EPM) and ethylene–propylene–diene terpolymers (EPDM), with different chemical compositions, have been studied by means of the combined kinetic analysis. Until now, attempts to establish the kinetic model for the process have been unsuccessful and previous reports suggest that a model other than a conventional nth order might be responsible. Here, a random scission kinetic model, based on the breakage and evaporation of cleavaged fragments, is found to describe the degradation of all compositions studied. The suitability of the kinetic parameters resulting from the analysis has been asserted by successfully reconstructing the experimental curves. Additionally, it has been shown that the activation energy for the pyrolysis of the EPM copolymers decreases by increasing the propylene content. An explanation for this behavior is given. A low dependence of the EPDM chemical composition on the activation energy for the pyrolysis has been reported, although the thermal stability is influenced by the composition of the diene used.     

Study on Self-assembly of Poly(ethylene glycol)- block-poly(γ-benzyl L -glutamate)-graft-poly(ethylene glycol) Copolymer and Poly(γ-benzyl L -glutamate)- block-poly(ethylene glycol) Copolymer in Ethanol

Poly(ethylene glycol)-block-poly(γ-benzyl L-glutamate)-graft-poly(ethylene glycol) (PEG-b-PBLG-g-PEG) copolymer was synthesized by the ester exchange reaction of poly(γ-benzyl L-glutamate)-block-poly(ethylene glycol) (PBLG-block-PEG) copolymer with PEG chain, and PBLG-block-PEG copolymer was prepared by a standard N-carboxyl-γ-benzyl-L-glutamate anhydride (NCA) method. Nuclear magnetic resonance (NMR) spectroscopy was used to confirm the components of PBLG-block-PEG and PEG-b-PBLG-g-PEG. The self-association behaviors of PBLG-block-PEG and PEG-b-PBLG-g-PEG in ethanol were investigated by transmission electron microscopy (TEM), dynamic laser scattering (DLS), and viscometry. The experimental results revealed that the different molecular structures could exert marked effects on the self-assembly behaviors of PBLG-block-PEG and PEG-b-PBLG-g-PEG in ethanol. PBLG-block-PEG and PEG-b-PBLG-g-PEG could self-assemble to form polymeric micelles with a core-shell structure in the shapes of plump spherical and regular rice-like, respectively. Effects of the introduction of PBLG homopolymer on the average particle diameter of the micelles of PBLG-block-PEG and PEG-b-PBLG-g-PEG and influence of testing temperature on the critical micelle concentration of different copolymers were studied.     

The Synthesis of Poly(ethylene oxide)-Block-Polybutylacrylate

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Bis(imino)pyridine–iron(II) complexes for ethylene polymerization

Ethylene polymerization was carried out using new late transition metal 2,6-bis(imino)pyridine catalysts containing different substituents (H, NO₂, and OCH₃) at the para position of the pyridine ring, activated by methylaluminoxane. Effects of polymerization parameters such as ethylene pressure, reaction temperature, hydrogen concentration and structure variation on the catalysts activities and polymer properties were investigated. Introducing the functionality in the para-position of the pyridine ring of the catalysts had remarkable effect on the polymer properties as well as the catalysts activities.     

Synthesis and Reactivity of Hydroxypoly(ethylene oxide) propyl–b–polydimethylsiloxane–b–propyl hydroxypoly(ethylene oxide)

A series of α, ω–bishydroxyl terminated PDMS, hydroxypoly(ethylene oxide) propyl–b–polydimethylsiloxane–b–propyl hydroxypoly(ethylene oxide) (HPEO–PDMS–HPEO) was prepared by a hydrosilation reaction of monoallyloxy substituted poly(ethylene oxide) with α,ω–bishydrogen terminated PDMS (HPDMS) that obtained via acid–catalyzed ring–opening polymerization of octamethylcyclotetrasiloxane with 1,1,3,3–tetramethyldisiloxane. Chloroplatinic acid was employed as the catalyst of hydrosilation. The molecular weight of HPEO–PDMS–HPEO could be controlled easily by varying the chain length of HPDMS. FTIR and ¹H–NMR spectroscopy were used to identify the structure of HPEO–PDMS–HPEO and HPDMS. The conversion of Si–H bond to Si–C bond was affected by the catalyst amount, reaction time and temperature. It was found that the optimum condition of hydrosilation reaction was the catalyst amount of 22 μg/g and 5 h time at 100°C. Synthesized HPEO–PDMS–HPEO showed good storage stability at ambient temperature. Urethane reaction of OH and NCO group revealed that HPEO–PDMS–HPEO was more reactive toward to diisocyanate than α, ω –bishydroxylbutyl terminated PDMS.     

Thermal characterization of biodegradable methoxy poly(ethylene glycol)-b-poly(d,l-lactide)/methoxy poly(ethylene glycol)-b-poly(ε-caprolactone) blend nanoparticles

Biodegradable methoxy poly(ethylene glycol)-b-poly(d,l-lactide) (MPEG-b-PDLL) and methoxy poly(ethylene glycol)-b-poly(ε-caprolactone) (MPEG-b-PCL) diblock copolymers were synthesized by ring-opening polymerization of DLL and CL monomers in bulk using stannous octoate, and MPEG as the initiating system. Surfactant-free MPEG-b-PDLL/MPEG-b-PCL blend nanoparticles were prepared by the nanoprecipitation method. The influences of block length and blend ratio on morphology, average size, and thermal properties of the blend nanoparticles were determined. The blend nanoparticles were spherical in shape. The average particle sizes slightly decreased as the MPEG-b-PCL blend ratio increased. ¹H-NMR and thermogravimetry revealed the different MPEG-b-PDLL/MPEG-b-PCL blend ratios of the nanoparticles. Differential scanning calorimetry showed that the MPEG-b-PCL crystallinity steadily decreased as the MPEG-b-PDLL blend ratio increased, suggesting miscible blending between the MPEG-b-PDLL and MPEG-b-PCL in the amorphous phase of the nanoparticle matrix.     

Photochemical reaction oftrans-di(α-naphthyl)ethylene with diphenylamine

Diphenylamine adds to the ethylene bond of excitedtrans-di(α-naphthyl)ethylene (1). Dependence of the quantum yields of mono- and bi-molecular reactions of1,cis-di(α-naphthyl)ethylene2, and dihydropicene3 on amine concentration was studied. On this basis and theoretical analysis of the kinetic scheme a conclusion was drawn that amine interacts with excited1 with a diffusion-limited rate but has no effect on the photochemical activity of2 and3. The reaction mechanism was discussed.     

Solubility of naphthalene in aqueous solutions of poly(ethylene glycol)–poly(propylene glycol)–poly(ethylene glycol) triblock copolymers and (2-hydroxypropyl)cyclodextrins

The solubility of naphthalene was investigated in aqueous solutions of triblock copolymers poly(ethylene glycol)–poly(propylene glycol)–poly(ethylene glycol) (PEG–PPG–PEG) and (2-hydroxypropyl)cyclodextrins. The results with solutions of the individual solubilizers were as expected: the solubility enhancement was much higher with a micelle-forming copolymer than with the non-micellizing one and with (2-hydroxypropyl)--cyclodextrin (HPBCD) than with (2-hydroxypropyl)--cyclodextrin (HPACD). Although the formation of inclusion complexes between HPACD and PEG and between HPBCD and PPG is well established, the naphthalene solubility in mixed solutions does not significantly deviate from that predicted for a mixture of independent solubilizers. Thus the interactions between HPCD and PEG–PPG–PEG copolymers are not strong enough to disrupt micelles and aggregates formed by those copolymers. In fact, slight synergetic deviations were observed with the micellizing copolymer, indicating the existence of ternary naphthalene/HPCD/copolymer interactions. For pharmaceutical applications, it is important that the solubilization efficacy of PEG–PPG–PEG copolymers and that of cyclodextrins modified by the 2-hydroxypropyl group would not be compromised if these two types of solubilizers were co-administered.     

Poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene)oxide triblock copolymers at the water/air interface and in foam films

The behavior of commercial poly(ethylene oxide)(PEO)–poly(propylene oxide)(PPO)–PEO triblock copolymers at the water/air interface and in microscopic foam films is studied. In aqueous solution these amphiphilic nonionic substances exhibit a surfactant-like aggregation and adsorption behavior. Even below the critical micelle concentration (cmc) the surface concentration is so high that the PEO chains are squeezed and protrude into the solution in order to accommodate to the situation at the interface. As evidenced by measurements of the ellipticity of light reflected from the free surface of the solution a PEO brush is created at the fluid interface. The microscopic foam film is used as a tool for investigating the normal interaction between two PEO brushes facing each other. Stable foam films are obtained at concentrations below the cmc and steric repulsion predominates (in 0.1 M NaCl). A brush-to-brush contact is established only at higher capillary pressures and the disjoining pressure isotherm follows de Gennes' scaling prediction. At lower pressure a softer steric repulsion occurs. It is governed by the bulk copolymer concentration and hence is fundamentally different from the brush-to-brush repellency. On the whole PEO–PPO–PEO copolymers behave as nonionic surfactants, but the large size of their molecules exemplifies the excluded-volume features. Received: 13 July 1999/Accepted: 27 July 1999     

Self-diffusion in poly(N -vinyl pyrrolidone) – poly(ethylene glycol) systems

 We have applied the PFG NMR technique to investigate the translational mobility in the PVP-PEG system as a function of composition and temperature at the stages of PVP-PEG complex formation, its swelling, and dissolution in excess of liquid PEG. It has been found that the variations of the spin-echo attenuation with PEG content, water amount, and temperature reflect the different stages. The first two stages are characterized by a distribution of the self-diffusion coefficients of PEG involved in the network. The dissolution shows two diffusion coefficients; the fast one is attributed to PEG molecules, the slow one to the associates of PEG and PVP. The temperature dependencies can be described by an Arrhenius law with an activation energy depending on the composition of the blend. The concentration dependence of the PEG self-diffusion coefficients in the blend occurred to be independent of the molecular weight of PVP. The results are discussed in terms of the Mackie-Meares model. Received: 23 August 2000 Accepted: 19 October 2000     

Nickel(II)-α-diimine complexes containing naphthyl substituents for ethylene polymerization under low ethylene pressure

Two new α-diimine containing Ni(II) complexes, {bis[N,N′-(2,6-dimethyl-4-naphthylphenyl)imino]-1,2-dimethylethane}dibromonickel 3a and {bis[N,N′-(2-methyl-4-naphthylphenyl)imino]-1,2-dimethylethane}dibromonickel 3b were synthesized and characterized. The crystal structures of representative ligand 2a and its complex 3a were determined by X-ray crystallography. Complex 3a bearing 2,6-dimethyl and 4-naphthyl groups, activated by diethylaluminum chloride (DEAC), shows high catalytic activity for the polymerization of ethylene [4.43 × 10⁶ g PE/(mol Ni h bar)]. Interestingly, complexes 3a and 3b bearing the naphthyl substituent in the para-aryl position produced dendritic polyethylenes (branching degree, 3a: 112, 118, and 147; 3b: 113, 127, and 151 branches/1,000 C at 20, 40, and 60 °C, respectively). The dendritic polyethylene particle size obtained by 3a and 3b/DEAC can be controlled in the 1–20 nm range under low ethylene pressure (diameter, 3a: 18.31, 14.44, and 11.09; 3b: 12.29, 8.98 and 6.27 nm at 20, 40, and 60 °C, respectively) and could be expected to produce a nano-targeted drug carrier after modification with water-soluble oligo(ethylene glycol).     

Aggregation Behavior of Poly(ethylene glycol)-block-poly (γ-benzyl L-glutamate)-graft-poly(ethylene glycol) Copolymer and its Blends with Poly(γ-benzyl L-glutamate) Homopolymer in Mixed Solvents

Poly(ethylene glycol)-block-poly(γ-benzyl L-glutamate)-graft-poly(ethylene glycol) (PEG-b-PBLG-g-PEG) copolymer was synthesized by the ester exchange reaction of PBLG-block-PEG copolymer with mPEG. The self-association behaviors of PEG-b-PBLG-g-PEG and its blends with PBLG homopolymer in the mixtures of ethanol and dimethylformamide (DMF) were investigated by transmission electron microscopy (TEM), dynamic light scattering (DLS), and viscometry. Effects of the introduction of PBLG homopolymer, the grafting ratio, and the DMF content on the self-association behaviors of PEG-b-PBLG-g-PEG copolymer in the mixtures of ethanol and DMF were mainly researched. It was revealed that PEG-b-PBLG-g-PEG copolymer could self-assemble to form polymeric micelles with a core-shell structure in various shapes from different preparation conditions. The critical micelle concentration (CMC) and the average particle diameter of the micelles formed by PEG-b-PBLG-g-PEG copolymer in the mixed solvents also changed with different preparation conditions.     

Novel thermogelling poly(ε-caprolactone-co-lactide)-poly(ethylene glycol)-poly(ε-caprolactone-co-lactide) aqueous solutions

The aqueous solutions of poly(e-caprolactone-co-lactide)-poly(ethylene glycol)poly(e-caprolactone-co-lactide) undergoing sol-gel transition as the temperature increases from 20 to 50℃were successfully prepared. The thermogelling triblock copolymers were synthesized by subtle tuning of the chemical composition and the hydrophilicity/hydrophobicity balance. The sol-gel transition was studied focusing on structure-property relationship. The amphiphilic copolymer formed micelles in aqueous solutions. It is believed to have potential applications in drug delivery and tissue engineering.     

Dielectric polarization of cross-linked poly(ethylene oxide)—phenomenology

Results of dielectric relaxation studies will be discussed. It turns out that competition of electric and structural relaxation coins permittivity and as a result conductivity mechanism at low temperature. It dominates long-ranging relaxation in the molten state. In the opposite limit of temperature, cross-linked poly(ethylene oxide) (PEO) with low mesh size can be transferred into super-cooled liquid state. Then, PEO behaves like a hydrogen-bonded liquid since crystallization is strongly suppressed. As a result, one observes slow Debye-like relaxation at low temperature. Beyond the low-frequency region, there appears an extended region between crossings of impedance components, where Z′ ≈ Z″ at acceptable approximation. It is coined by damped oscillation under action of the electric field. These effects lessen with increasing mesh size of the sample as clearly shown by M″(ω) spectra. The dipole moment of the PEO samples in molten state decreases only slightly with increasing mesh size.     

Ethylene Polymerization-Induced Self-Assembly (PISA) of Poly(ethylene oxide)-block-polyethylene Copolymers via RAFT

Poly(ethylene oxide) (PEO) with dithiocarbamate chain ends (PEO–SC(=S)−N(CH₃)Ph and PEO–SC(=S)−NPh₂, named PEO-1 and PEO-2 , respectively) were used as macromolecular chain-transfer agents (macro-CTAs) to mediate the reversible addition–fragmentation chain transfer (RAFT) polymerization of ethylene in dimethyl carbonate (DMC) under relatively mild conditions (80 °C, 80 bar). While only a slow consumption of PEO-1 was observed, the rapid consumption of PEO-2 led to a clean chain extension and the formation of a polyethylene (PE) segment. Upon polymerization, the resulting block copolymers PEO-b-PE self-assembled into nanometric objects according to a polymerization-induced self-assembly (PISA).     

Crystallization of Poly(ethylene adipate) within γ-Phase Poly(vinylidene fluoride) Matrix

The effects of PEA on the γ-phase PVDF crystal structure and the crystallization of PEA within the pre-existing γ-phase PVDF spherulites have been investigated by optical microscopy(OM), infrared spectroscopy(IR) and scanning electron microscopy(SEM). The results demonstrate that the γ-phase PVDF spherulites consist of the lamellae exhibiting a highly curved scroll-like morphology and develop preferentially in PEA-rich blend. With increasing PEA concentration, the scroll diameter increases and the scrolls are better separated from each other. PEA crystallizes first in the interspherulitic region and transcrystalline layer develops. Subsequently, the transcrystalline layer of PEA continues to grow within the γ-phase PVDF spherulites, e.g., in the region between the scrolls, until impinging on other PEA transcrystalline layers or spherulites. The crystallization kinetics results indicate that the growth rate of PEA crystals in the intraspherulitic region of γ-phase PVDF shows a positive correlation with content of PEA, but a negative one with the crystallization temperature of γ-phase PVDF.     

pH-responsive star-shaped functionalized poly(ethylene glycol)-b-poly(ε-caprolactone) with amino groups

Functional star-shaped 4-arm poly(ethylene glycol)-b-poly[(ε-caprolactone-co-γ-amino-ε-caprolactone)] (4-arm PEG-b-P(CL-co-ACL) was synthesized through ring-opening polymerization. The structure of the copolymer was confirmed by ¹H NMR, Fourier transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC). To further understand the copolymers, the difference of the conversion rate between ε-caprolactone (CL) and γ-(carbamic acid benzyl ester)-ε-caprolactone (CABCL) and the detailed deprotection condition were studied. The thermal property of the copolymer was analyzed by WAXR and differential scanning calorimetry (DSC), which demonstrated that the thermal property could be well adjusted. The pH-responsive behavior of the copolymers was studied in detail by dynamic light scattering (DLS), pH titration, and pyrene fluorescence methods, which indicated that it could form micelles and exhibit pH responsibility. Moreover, the copolymer was nontoxic and had good biocompatibility according to the results by 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di-phenytetrazoliumromide (MTT) assay.     

Recovery of Uniaxially Stretched Amorphous Poly(ethylene terephthalate) Film

Thedeformationandrecoveryofamorphouspolymerwerestudiedinrecentyears'-'.SomeresearcherssuggestedthatthepostyieldingdeformationofamorphouspolymerwasmadeupoftwocomponentsfromDSC--volumeanddimensionrecoveryexperiments'-'.Butunderstandingaboutthisprocesswasincomplete,especiallyaboutthemotionofthechain.Theaimofthisarticlewastoinvestigate,onamacroscopicscale,thedifferentcomponentsoflargescaletensiledeformationbyobservingtherecoveryofuniaxiallystretcheda-PETfilmasafunctionoftime,temperatureanddrawra…     

Polyethylenimine (PEI)g-comb-poly(ethylene glycol)-transferrin(I): Tumor-targeted Vector for Gene Delivery In-vitro

A new vector, PEG as a core, low Mw PEI was grafted to PEG, and transferrin was conjugated the co-polymer to form PEI-g-PEG-transferrin1,2. NMR, FT-IR and TGA spectroscopy confirmed the structures of activated PEG and the final products. The MW of PEI-g-P…